Module 13
Introduction
In this module, you will use your knowledge of the male and female reproductive systems to learn more about the medical terms associated with reproduction, pregnancy, and childbirth. When you complete this module, you should also be familiar with pathologies that are related to pregnancy, childbirth, and the newborn. You will recognize terms for tests and procedures that are used to diagnose these problems and have a good understanding of the surgical and therapeutic interventions used to treat them. In addition, you will learn more about sexually transmitted diseases and the terminology used to discuss their diagnosis and treatment. As you work through this module, you may need to refer to the basics of word structure that were introduced in Module 1.
Objectives
In this module, you will learn to:
- Demonstrate a general understanding of fertilization, implantation, and growth of the embryo by selecting the correct terms to match descriptions.
- Define or select the correct meanings of terms related to pregnancy, labor, and the newborn.
- Match contraceptives with their characteristics.
- Match sexually transmitted diseases with their characteristics.
1.1 Threaded Case Study: Jackie and Alan
Jackie and Alan have been married for nearly three years and are now hoping to start a family. Jackie's gynecologist has told her that she is healthy and there is no reason why she should expect problems with conception, pregnancy, or delivery. We'll follow Jackie as she and Alan look forward to having a child.
1.2 Coitus
The medical term for sexual intercourse, the sexual union of male and female, is coitus. The term copulation has the same meaning, although this term is more often used with respect to animals other than humans.
During coitus, the male ejaculates semen, or seminal fluid, from his urethra into the female vagina. In one ejaculation, between 150 and 350 million sperm are deposited. The semen and the flagellating tail-like projections of the spermatozoa help to propel them through the uterus and into the fallopian tubes.
1.3 Fertilization
When an ovum is released from the ovary, the fimbriae guide it into the fallopian tube. If ovulation occurs anytime from 72 hours before to 48 hours after coitus, a sperm cell may encounter the ovum in a fallopian tube and unite with it. This process is called fertilization or conception.
Each gamete (sex cell) has 23 chromosomes, half the number found in all other human body cells. When fertilization occurs, the two gametes form a single cell with a full complement of 46 chromosomes called a zygote.
The zygote then begins a process of rapid cell division as it continues its journey through the fallopian tube, eventually coming to rest in the uterus about 10 days after ovulation. The attachment of the zygote to the uterine wall is called implantation.
1.4 Embryo Development
At this point, the growing group of cells is called an embryo. It continues to develop, forming an outer layer of cells and an inner cell mass.
The inner cell mass becomes a structure with two cavities—the yolk sac, which produces blood cells, and the amniotic cavity. This cavity's inner membranous layer is the amnion, represented by the combining form amni/o. This combining form is found in a number of obstetric terms. For example, the term amniotic means pertaining to the amnion. During pregnancy, the amniotic cavity becomes a protective sac filled with amniotic fluid in which the embryo floats during development.
1.5 Placenta
The outermost layer of the membranes surrounding the embryo is called the chorion, represented by the combining form chori/o.
Together with the endometrial lining of the uterus, the chorion gives rise to the placenta, a highly vascular organ that serves as a bridge to the maternal circulation for the exchange of nutrients and wastes. The embryo is anchored to the uterine wall by the placenta.
1.6 HCG in Pregnancy Testing
During pregnancy, the placenta secretes its own hormone, human chorionic gonadotropin (HCG). The suffix -tropin means that which stimulates.
HCG promotes the continued secretion of progesterone by the corpus luteum until about the third month of pregnancy, when the placenta itself completely assumes that function.
HCG is filtered from the blood by the kidneys and is excreted in the urine of a woman who is pregnant; it is this component that is detected by pregnancy tests.
After three months of monitoring her temperature, Jackie's normally regular menstrual period does not appear. A pregnancy test using a sample of her urine indicates the presence of HCG. Jackie is pregnant!
1.7 Pregnancy
The terms pregnancy, gestation, and cyesis all refer to the period of growth and development from fertilization of the ovum until birth. Because it occurs before (pre-) birth (nat/o), this is also called the prenatal period.
Other terms for prenatal are antenatal and antepartum; ante- also means before.
In humans, the average pregnancy lasts approximately 9 months. The estimated date of delivery (EDD) is 280 days from the start of the last menstrual period (LMP). This calculation may be confirmed as pregnancy progresses by comparison to the apparent gestational age (GA) of the fetus based on physical examination and fetal ultrasound examination.
The course of a pregnancy can be divided into three 3-month periods called trimesters. The first trimester is from the date of the LMP through the third month; the second trimester is the period of months 4, 5, and 6; and the third trimester refers to the 7th, 8th, and 9th months.
1.8 Terms of Pregnancy History
Specific terminology can also be used to convey information about a woman's history of pregnancy as well as the fetus. For instance, Jackie is now considered to be gravid. This term means pregnant, and gravida refers to a pregnant female.
More specifically, Jackie is expecting her first child—and believe it or not, there is a term to express just that. Jackie's physician notes in her record that she is gravida I, meaning that she is pregnant for the first time. Another way to say this is to combine the prefix primi- with the suffix -gravida to form the term primigravida, which also refers to a woman who is pregnant for the first time.
Suppose that a woman is pregnant for the second time. Then she is referred to as gravida II. The term multigravida is used to indicate any female who has been pregnant more than one time; the prefix multi- means many. The term nulligravida refers to a woman who has never been pregnant. The prefix nulli- means none.
1.9 Fetus
After the eighth week of gestation, the developing child is no longer called an embryo; it is called a fetus. The combining form fet/o means fetus. The term fetal is an adjective that means pertaining to the fetus.
A number of terms use fet/o as a root. For instance, radiographic imaging of the fetus is called fetography.
Monitoring the fetal heartbeat through the mother's abdominal wall is called fetoscopy. This procedure uses a special stethoscope called a fetoscope. Keep in mind, however, that an endoscope for viewing the fetus in utero (within the uterus) is also called a fetoscope.
Ultrasound imaging of the growing fetus uses high-frequency sound waves to generate images of the fetus and some of its internal organs. Conventional ultrasound images are two-dimensional, but newer equipment produces very clear three-dimensional images, such as the one illustrated here.
2.1 Threaded Case Study: Early Labor
Jackie's pregnancy progresses normally. Then one evening, as Jackie and Alan return home after a quiet dinner out, Jackie begins to feel discomfort in her back and mild contractions of her enlarged abdomen. Labor has begun!
Labor, the process of giving birth, begins with the dilation of the cervix. Dilation refers to the process of being stretched, widened, or enlarged. When the cervix dilates, the passageway between the uterus and the vagina becomes larger and wider.
Uterine contractions begin as periodic mild sensations of firmness in the abdominal wall, often accompanied by discomfort in the lower back. As labor progresses, the contractions become stronger, more regular, and more frequent. They also last for progressively longer periods, eventually occurring every two to three minutes and lasting more than a minute. These contractions cause the cervix to dilate further.
The shortening and thinning of the cervix during labor is called effacement. This causes the mucus plug that fills the cervical canal to loosen; it is then expelled through the vagina.
2.2 Rupture of Amnion
The loss of clear fluid from the vagina is a sign that the membranes surrounding the fetus have ruptured and amniotic fluid is leaking from the amniotic sac. In lay terms, it may be said that "the water breaks," or "the bag of waters break." This may occur as a slow trickle of fluid or as a sudden gush. Membranes may rupture at any point during labor. Sometimes this is the first sign that labor has started, but more often it occurs in the later stages.
Forceful tearing or rupture of the amnion is called amniorrhexis.
2.3 Threaded Case Study: Labor Continues
When Jackie's contractions are becoming intense and are about 10 minutes apart, Alan drives her to the hospital, which is near their home. They have made advance hospital arrangements for delivery and have called ahead to let the maternity department know that Jackie is in labor.
When Jackie is settled in her room and has been examined by her obstetrician, an electronic fetal monitor (EFM) is strapped to her abdomen. This instrument provides a graphic display and a paper tape record of the fetal heartbeat and the uterine contractions while Jackie's labor continues.
2.4 Parturition
When the cervix is adequately effaced and dilated, delivery of the baby begins. The term parturition refers to the process of giving birth. Powerful uterine contractions expel the fetus from the uterus and through the vagina.
Following the birth of the child, the placenta is expelled from the uterus, together with the fetal membranes, as seen in this illustration. The expelled placenta and membranes are called the afterbirth, and their expulsion is called the placental stage of labor.
2.5 Postpartum
As soon as the child is delivered, it is placed on the maternal abdomen until the placental stage of labor is complete and the umbilical cord has been severed.
You will recall from earlier in this lesson that antepartum and prenatal mean before birth. The prefix post- means after; thus, both postpartum and postnatal refer to the period of time after delivery. For example, postpartum care is the care given to the mother after she has given birth.
Although these terms are used interchangeably, there is a technical difference; postpartum refers more specifically to the status of the mother, while postnatal relates more directly to the status of the child. This is because -partum is related to parturition and refers to the process of giving birth, whereas -natal refers to the process of being born.
2.6 Terms Denoting Production of Viable Offspring
Now that Jackie has given birth to a live child that has developed sufficiently to live outside the uterus, Jackie is described as parous. This is because the combining form par/o means producing or bearing viable offspring. The term parous and the suffix -para refer to a female who has produced viable offspring.
More specifically, since Jackie has produced just one viable offspring, she is now called primipara (primi- means first), or para I, until she has more than one child.
A woman who has produced two children is called secundipara, or para II. The terms para III and tripara mean a woman has produced three children; quadripara means four. Multipara means more than one.
Is there a special designation for a woman who has never given birth to a live child? Yes. She is referred to as nullipara; recall that the prefix nulli- means none. This is the same as para 0.
2.7 Threaded Case Study: Neonate
Jackie and Alan can now announce that they have a healthy baby girl.
You will recall that nat/o means birth. The prefix neo- means new. Thus, a newborn infant is called a neonate.
The neonatal period is that time in an infant's life from birth to one month of age.
A neonatologist is a physician who specializes in the care of the newborn.
3.1 Pseudocyesis
Before we begin the discussion of abnormalities that occur during pregnancy, let's look at a condition that is not pregnancy, but may seem to be.
Pseudocyesis is the medical term for false pregnancy. It is derived from the prefix pseudo-, meaning false, and -cyesis, which you will recall means pregnancy. This condition is characterized by absence of menses and is accompanied by other signs of pregnancy but without conception. This condition is usually psychogenic; you may recall from Module 6 that psychogenic means produced by the mind. Although the most common cause is a psychological disorder related to an intense desire to be pregnant, pseudocyesis may also have a physical cause, such as abdominal neoplasia (tumor growth) or a hormonal disorder.
3.2 Extrauterine Pregnancy
The prefix extra- means outside, and uterine means pertaining to the uterus. Therefore, an extrauterine pregnancy is one that occurs outside the uterus. Another term for this occurrence is ectopic pregnancy. This term is derived from the prefix ecto-, which also means outside, and the combining form top/o, meaning place, position, or location. Thus, ectopic means pertaining to outside the usual location, so an ectopic pregnancy also refers to one that occurs outside the uterus, as depicted in the illustration. You'll note that the prefix has been shortened in forming this term.
An ectopic or extrauterine pregnancy is an abnormal pregnancy in which the zygote implants outside the uterus, often in a fallopian tube. In lay terms, this is referred to as a tubal pregnancy.
Ectopic pregnancies are not viable and cannot be saved. As the zygote grows, there is risk of rupture of the fallopian tube, sometimes accompanied by life-threatening hemorrhage. Some ectopic pregnancies resolve themselves, requiring no treatment. Sometimes medication (methotrexate) is given to destroy the zygote, allowing the body to resolve the pregnancy over a period of several weeks. The usual treatment, however, is surgery, either laparoscopic surgery or laparotomy, depending on the patient's status. You will recall that laparotomy is a surgical incision through the abdominal wall.
3.3 Hypertensive Disorders of Pregnancy
Preeclampsia is a disorder that occurs only during pregnancy and the postpartum period and affects both the mother and the unborn baby. It can be fatal. It is a rapidly progressive condition characterized by hypertension, edema, and proteinuria. Preeclampsia occurs in 5-8% of all pregnancies, usually in mid to late pregnancy. It is believed to be caused by an improper balance in the chemical signals across the placenta that normally ensures adequate nutritional blood supply to the fetus. There is apparently an inherited tendency to this condition, as women whose mothers had preeclampsia are more likely to have it than those with no family history of it. Closely related conditions are pregnancy-induced hypertension (PIH) and toxemia of pregnancy.
When the symptoms also include seizures and/or coma, the condition has progressed to eclampsia. It is significant to note that more women die from preeclampsia than eclampsia and one is not necessarily more serious than the other.
HELLP syndrome is a condition of pregnancy characterized by hemolysis, elevated liver enzyme levels, and a low platelet count. HELLP syndrome is not common and many investigators consider it to be a variant of preeclampsia, but it may be a separate condition.
Proper prenatal care is essential to diagnose and manage these conditions.
3.4 Fetal Death
The termination of a pregnancy before the fetus is viable is called an abortion. If there are no signs of life before 24 weeks of pregnancy, this is known as a miscarriage, or spontaneous abortion. The illustration shows three types of spontaneous abortion. If the pregnancy is terminated intentionally, this is termed a therapeutic abortion or an elective abortion. If the products of conception are not completely expelled from the uterus, it is called an incomplete abortion and is treated by performing a D & C. You will recall from Module 12 that D & C stands for dilation and curettage, a surgical procedure that involves scraping tissue and debris from the endometrium.
Stillbirth is defined as any baby born with no signs of life after 24 weeks of pregnancy. Some authorities divide the pregnancy at 20 weeks, rather than 24, with respect to these designations.
3.6 Labor Induction and Acceleration
When the cervix is partially dilated but labor is not proceeding well, physicians or midwives sometimes cut the amniotic membrane to induce or accelerate labor. This procedure is called an amniotomy.
Another method of inducing labor is the use of medication. The natural hormone oxytocin causes the uterus to contract and initiates the ejection of milk from the breasts. When delivery is delayed beyond a reasonable period, a preparation of synthetic oxytocin, given as an intravenous infusion, can be used to induce labor. Oxytocin is also administered to accelerate labor if it stalls after it has begun.
3.7 Dystocia
Dystocia is defined as abnormal or difficult labor. The opposite of dystocia is eutocia, which is normal labor. Dystocia defines situations in which labor is not progressing normally, placing mother or child, or both, at risk.
Dystocia may be caused by any of the following circumstances during labor: (1) abnormalities of expulsive forces; (2) abnormalities of presentation, position, or development of the fetus; and (3) abnormalities of the maternal bony pelvis or birth canal. Combinations of these three conditions may interact to cause a dysfunctional labor.
Shoulder dystocia is a delivery circumstance in which the fetal head has emerged but one or both fetal shoulders are impacted on the bones of the maternal pelvis, preventing completion of the delivery. Additional maneuvers are required to deliver the fetus when the usual gentle downward traction (pull) has failed.
Dystocia is often an indication for operative delivery. In this surgical procedure, called a cesarean section, the abdomen and uterus are incised and the baby is removed (as shown in the illustration). The procedure is abbreviated C-section or CS.
|
|
The cesarean section is named for Julius Caesar, whom legend tells us was born through an incision in his mother's abdomen in about 100 B.C. |
3.9 Placental Complications
Abruptio placentae (Fig. A) refers to separation of the placenta from the uterine wall after the 20th week of gestation and prior to birth. This condition is also called placental abruption. Except in rare cases of trauma, the cause is not known. It is sometimes associated with preeclampsia and sometimes with a sudden change in the volume of the uterus, for example, in cases of amniorrhexis or the birth of a first twin. If the separation is complete or nearly complete, the fetus will die unless an immediate cesarean delivery is performed.
Placenta previa (Fig. B) is a condition of pregnancy characterized by abnormally low implantation of the placenta in the uterus so that it covers the internal opening of the uterine cervix. This is the most common cause of painless bleeding in the third trimester of pregnancy. It is a very serious condition, especially when the cervical opening is completely occluded, due to the risk to both mother and child of hemorrhage during delivery. This condition is usually diagnosed using fetal ultrasound and a cesarean delivery is then performed.
3.10 Pelvimetry
An obstetric condition in which a mother's birth canal is too small or her baby's head is too large to permit a normal vaginal delivery is called cephalopelvic disproportion (CPD). You will recognize in this term the word parts that refer to a size difference pertaining to the (fetal) head and the (maternal) pelvis.
Obstetricians usually evaluate the maternal pelvic bone structure early in pregnancy. The measurement of the capacity and dimensions of the pelvic cavity is a process called pelvimetry. This term is derived from pelv/i, meaning pertaining to the pelvis, and -metry, meaning measurement.
If the size of the maternal pelvis is questionable for a normal vaginal delivery, a careful watch is kept on the size of the developing fetus and arrangements are made for a cesarean birth, if needed. Fetal head size is monitored by ultrasound measurements.
3.11 Fetal Presentation
During a normal birth, the fetus's head is the first part of its body to enter the mother's pelvis. Thus, it is called a cephalic birth, or cephalic presentation. Cephalic means pertaining to the head.
Occasionally, the buttocks or feet may come first; this is called a breech birth, or breech presentation. When the feet come first, the presentation may be called a footling breech. Women do not labor as effectively with a breech presentation because the fetal head is not pressing against the cervix during contractions. A breech presentation can also cause problems because the head, the largest part of the fetus's body, may become trapped since its shape does not mold to the mother's pelvis during labor. Prolapse of the cord into the vagina with interruption of the fetal blood supply is also a risk.
The fetus almost always lies in a vertical position, but in rare instances, it may lie transversely, with its back presenting. This type of presentation almost never proceeds to a normal vaginal delivery. If the fetus cannot be turned in utero to a more advantageous presentation, a cesarean section must be performed.
3.12 Episiotomy
During the delivery, the physician or midwife may perform an episiotomy, a surgical incision of the perineum to enlarge the vaginal opening for delivery (as seen in the illustration). The purpose of this procedure is to prevent traumatic tearing of the perineum.
Following delivery, the vagina and perineum will need to be sutured if there has been an episiotomy or traumatic tearing. Suturing of the perineum is called perineorrhaphy, and suturing of the vagina is colporrhaphy.
3.13 Sonography
Most pregnancies are monitored with several fetal ultrasound examinations during the gestational period. As you have noted throughout this module, sonography (diagnostic ultrasound procedure) aids in assessment of gestational age, fetal head size, and fetal abnormalities.
Early detection of developmental abnormalities, such as heart defects, is possible with sonography. Some types of abnormalities can even be repaired surgically while the fetus is still in utero. Some defects are so severe as to prevent survival, in which case the parents have the option to terminate the pregnancy.
3.14 Maternal Blood Screening
Certain tests performed on the mother's blood serum are indicators of potential problems with the fetus. Technical advances made over the past 20 years now make it possible to identify pregnancies at higher-than-average risk of certain birth defects by drawing a simple blood sample.
The triple screen test is actually three tests: measurements of alpha fetoprotein (AFP) and the hormones estriol and HCG. The Quad test measures these three substances, plus a fourth substance called inhibin-A, which is a sensitive marker for detecting pregnancies at risk for Down syndrome.
Down syndrome is a genetic disorder that includes a combination of birth defects: some degree of mental retardation, characteristic facial features, and often heart defects, increased infections, problems with vision and hearing, and other health problems. The severity of all of these problems varies greatly among affected individuals. Down syndrome is one of the most common genetic birth defects, affecting approximately one in 800 to 1,000 babies. It generally is caused by an extra chromosome 21, and for this reason, it is sometimes referred to as trisomy 21. The risk of Down syndrome increases with the age of the mother.
3.15 Amniocentesis and Chorionic Villus Sampling
Amniocentesis (Fig. A) is a needle puncture of the abdomen and the uterine wall to obtain a sample of amniotic fluid for testing. The needle is guided using ultrasound imaging.
The fluid is analyzed to test for chromosomal abnormalities, genetic birth defects, and certain other conditions. It is the definitive prenatal test for Down syndrome.
It is recommended for women over age 35 and women with a previous child with a birth defect that can be diagnosed by amniocentesis. It is also advised for women with a family history of a genetic disorder and those with an abnormal triple screen test result.
There is little risk involved in this test. When needed, it is usually carried out between 15 and 18 weeks of pregnancy.
Chorionic villus sampling (CVS) (Fig. B) is a prenatal test that involves taking a tiny tissue sample from the chorion membrane, the outer layer of the fetal sac. This test does not involve perforation of the amnion and may be performed earlier than amniocentesis. The tissue is tested to diagnose or rule out certain birth defects. The test generally is performed between 10 and 12 weeks after a woman's last menstrual period.
3.16 Erythroblastosis Fetalis
Erythroblastosis fetalis is also called hemolytic disease of the newborn. It develops in an unborn infant because the mother produces antibodies that attack the fetus's red blood cells. This happens when the mother and the child have different blood types. The most common form is called ABO incompatibility, which can vary in its severity. The less common form is called Rh incompatibility, which more often causes a very severe anemia in the baby. The lay term for severe hemolytic disease of the newborn is blue baby. The term refers to the fact the child tends to be cyanotic, having a bluish complexion due to inadequate oxygen. Destruction of erythrocytes leaves the child with too little hemoglobin to provide sufficient oxygen to the tissues.
The term erythroblastosis refers to the presence of immature red blood cells (erythroblasts) in the fetal circulation. Normally these cells are found only in the bone marrow and do not enter the circulation until they are mature. They enter the circulation prematurely because the fetus's red blood cells are being destroyed and its bone marrow cannot produce mature red blood cells fast enough to replace those that have been destroyed.
The severity of this condition can vary greatly. In some instances, the baby has no symptoms of the disease. In other cases, the child may die before or shortly after birth. Signs of this problem in the neonate include hepatomegaly and/or splenomegaly, generalized edema, jaundice, and anemia. After birth, depending on the severity, a transfusion usually needs to be performed. When hemolytic disease is identified before birth, it can be treated in utero by intrauterine transfusion.
When an Rh negative mother delivers a child that is Rh positive, she is usually given an injection of RhoGAM, a type of vaccine to prevent the development of antibodies against Rh positive blood. This treatment prevents the most severe form of erythroblastosis in future pregnancies. This problem rarely occurs with first pregnancies because there is no mixing of maternal and fetal blood and the mother does not develop antibodies until after the blood contact that occurs with the first delivery.
You may wish to review Module 7, Lesson 2 for a better understanding of blood groups and the mechanism of blood group incompatibility.
4.1 Contraception
Contraception refers to the prevention of conception or impregnation by means of a device, medication, or method that alters or blocks one or more of the processes of reproduction. The devices and medications are called contraceptives.
Abstinence refers to the total avoidance of sexual intercourse. This is the only contraceptive option that does not involve medications, surgery, or devices and is also 100% effective.
4.2 Rhythm Method
The rhythm method is also known as fertility awareness or natural contraception. It is a natural family planning method that involves identification and recognition of fertile and infertile periods. Coitus is then limited to the infertile periods.
Fertility-awareness birth control methods are based on the fact that sperm may live in the female reproductive tract for up to 7 days and the ovum lives for only a day after ovulation. Thus, fertilization may occur up to a week after intercourse, but not more than 2 days after ovulation. The infertile days, then, begin 2 days after ovulation and continue until the next menstrual period.
There are several methods for determining which are the most fertile days of the menstrual cycle:
Calendar Rhythm Method: This method requires that a woman keep track of her cycle for a few months to determine her own individual pattern of ovulation. The pattern helps her determine when intercourse is most likely to result in conception.
Basal Body Temperature Method (see illustration): This method involves recording body temperature daily to determine when ovulation occurs. Body temperature rises two days prior to ovulation.
Symptothermal Method: A combination of the calendar and basal body temperature methods.
Ovulation Method: This involves checking the cervical mucus to determine the time of ovulation.
Ovulation Predictor Kits: Commercially available kits to test urine for specific hormones to determine when ovulation is about to occur.
Note that this fertility awareness can also be used to enhance the possibility of conception for couples who are hoping to conceive a child.
4.4 Barrier Contraceptive Methods
Barrier contraceptives are devices that prevent the sperm from entering the cervix. These include male and female condoms, diaphragms, and cervical caps.
A condom is a sheath that covers the penis. It is made of a thin, flexible material such as latex (rubber) and is worn during coitus to prevent impregnation or infection.
A diaphragm is a contraceptive device made of molded rubber or plastic and inserted to fit over the cervix uteri prior to sexual intercourse to prevent the entrance of spermatozoa.
A cervical cap is a latex, thimble-shaped device that is inserted into the vagina and fits snugly over the cervix. Suction keeps the cap in place. A cervical cap provides a barrier to block sperm from entering the uterus and prevents fertilization.
A female condom is a polyurethane (plastic) pouch with flexible rings at each end. It is inserted deep into the vagina like a diaphragm. The ring at the closed end holds the pouch in the vagina. The ring at the open end stays outside the vaginal opening.
Condoms, both male and female, are available at drugstores without a prescription and are disposable. They are quite effective as contraceptive devices and also serve to reduce the risk of sexually transmitted diseases. Diaphragms and cervical caps are prescribed and fitted by a physician.
4.5 Spermicides
Spermicides (as shown in the illustration) are substances, usually containing nonoxynol-9, that immobilize or kill sperm, preventing it from joining with an ovum. They are inserted deep into the vagina shortly before intercourse. They are available in a variety of contraceptive preparations, including foams, creams, jellies, film, and suppositories. A suppository is a solid that melts after it is inserted. Some suppositories consist of liquids contained in a gelatin shell that melts after insertion.
Contraceptive foams block the entrance to the uterus with bubbles. Contraceptive creams, jellies, film, and suppositories melt into a thick liquid throughout the vagina. They also block the entrance to the uterus. All of these contraceptives contain a spermicide.
The contraceptive sponge is a disposable, disk-shaped device made from polyurethane foam that fits over the opening of the cervix to block and absorb semen. It contains a spermicide. It is inserted before coitus and left in place for 24 hours. A string loop helps with removal. This product was removed from the
Spermicides are often used in conjunction with barrier devices. The use of a spermicide product with a condom, diaphragm, or cervical cap is more effective than either method used alone.
4.6 Hormones
Since hormones control the process of ovulation, the administration of hormones can be used as a contraceptive technique. When a woman says she is "on the pill" this means that she is taking oral contraceptive pills, tablets containing estrogen or a combination of estrogen and progesterone (Fig. A). Elevated blood levels of these hormones are signals to the body that pregnancy has already occurred and therefore ovulation does not take place.
Hormones can also be administered by injection. Depo-Provera is an injectable hormone that needs to be administered only every three months. Another hormone product, Lunelle, is designed for monthly injection.
The contraceptive implant system called Norplant involves the surgical insertion of six tiny units under the skin of the upper arm (Fig. B). This system provides continuous contraception for a period of five years. After that time, it must be surgically removed.
Another hormone administration method is the use of transdermal patches, adhesive pads that release medication over time for absorption through the skin. Trans- means through and dermal means pertaining to the skin. A new patch is applied weekly for three weeks. During the fourth week menstruation occurs. After a week without a patch, a new one is applied.
The vaginal contraceptive ring (NuvaRing) uses the same hormones as most birth control pills. It is a circular, flexible ring that is inserted into the vagina and releases hormones that prevent pregnancy. Unlike the diaphragm, the vaginal ring is not a barrier method and doesn't have to be in a specific position in the vagina. It is left there for three weeks and then taken out. During the week the ring is out, menstruation begins. After a week without the ring, a new one is inserted.
4.7 Intrauterine Devices (IUDs)
An intrauterine device (IUD) is a long-term method of birth control. It is a small plastic T-shaped stick that is placed inside the uterus by a physician. There are two basic types of IUDs manufactured in the
4.8 Sterilization
The various means of birth control discussed so far are considered reversible contraception. That is, the method can be discontinued when the woman wishes to become pregnant. Sterilization, on the other hand, is a permanent means of contraception. This term refers to the process of rendering an individual incapable of reproduction. Although excision of the uterus or the testes results in sterilization, these are extreme measures that are not needed or appropriate simply for contraception.
Tubal ligation (Fig. A) is a term for female contraceptive sterilization. This term refers to several sterilization procedures in which both uterine tubes are obstructed to prevent conception from taking place. This is usually accomplished laparoscopically but may also be done in conjunction with other abdominal surgical procedures, such as a cesarean section or laparotomy done for other purposes. Ligation means tying, and the lay term for having a tubal ligation is to have one's tubes tied. Tubal ligation can sometimes be reversed, but the success rate for the procedure is not great.
Male contraceptive sterilization is called a vasectomy (Fig. B) and is a minor surgical procedure that involves the excision of a portion of the vas deferens. While vasectomy is considered to be a permanent means of sterilization, it can sometimes be successfully reversed. The surgical procedure for reconnecting the vas deferens to reverse a vasectomy is called a vasovasostomy.
4.9 Infertility
Infertility is a condition of the reproductive system that impairs one of the body's most basic functions, the conception of children. Conception is a complicated process that depends upon many factors: the production of healthy sperm by the man and healthy ova by the woman; patent (open, unobstructed) fallopian tubes that allow the sperm to reach the ovum; the sperm's ability to fertilize the ovum when they meet; the ability of the zygote to become implanted successfully in the uterus; and sufficient embryo quality.
Finally, for the pregnancy to continue to full term, the embryo must be healthy and the woman's hormonal environment adequate for its development. When just one of these factors is impaired, infertility can result.
4.10 Diagnosing the Cause of Infertility
Couples are generally advised to seek medical help if they are unable to achieve pregnancy after a year of intercourse without the use of contraceptives.
The first step for a physician in diagnosis of infertility is to take a complete medical history of both the man and the woman. Many potential causes may be discovered by inquiring about previous diseases and treatments, including surgical procedures and medications, and the woman's history of menstruation and contraceptive practice. This interview will include a frank discussion of the couple's sexual practices to determine whether intercourse is taking place properly for conception.
The physician will then conduct a physical examination of both partners to determine their general state of health and to evaluate physical disorders that may be causing infertility. Sexually transmitted diseases must be ruled out.
If no cause has been determined at this point, more specific tests may be recommended. For women, the tests include an analysis of body temperature and ovulation and blood tests to determine hormone levels. Laparoscopy (Fig. A) may be performed to view the outer contours of the reproductive organs from within the pelvic cavity; a hysterosalpingography (Fig. B) may be appropriate to evaluate the internal surfaces of the uterus, ovaries, and uterine tubes and to determine whether the uterine tubes are patent.
For men, initial tests focus on semen analysis. At least two analyses of seminal fluid are done before reaching a conclusion or proceeding to further testing.
4.11 Infertility Treatments
When the cause of infertility has been determined, it may or may not be possible to correct the problem. Most infertility cases—85 to 90 percent—are treated with conventional therapies, such as drug treatment or surgical repair of reproductive organs. For example, hormone imbalances may be corrected by the administration of hormones; physical obstruction due to fibroids in the uterus may be corrected surgically.
When the male is unable to produce adequate live sperm, the female may be artificially inseminated with sperm from a donor. Artificial insemination involves placement of the sperm into the cervix or directly into the uterus. Intrauterine placement is usually more successful.
When these methods are not appropriate or are not successful, for example, when women have blocked or absent fallopian tubes or when men have low sperm counts, in vitro fertilization (IVF) offers a chance at parenthood to couples who otherwise would have no hope of having a biologically related child. This procedure allows the mother's ova to be fertilized outside the body and then implanted in the uterus of either the biological mother or a surrogate (substitute) mother to carry to term.
In IVF, ova are surgically removed from the ovary and mixed with sperm outside the body in a Petri dish. In vitro is a Latin term meaning in glass. After about 40 hours, the eggs are examined to see if they have become fertilized by the sperm and are dividing into multiple cells. These active zygotes are then placed directly into the woman's uterus, thus bypassing the fallopian tubes.
Depending on the limitations of the couple, IVF may be carried out with donor sperm, donor ova, or donor embryos. Sperm, ova, and embryos can all be frozen for later implantation.
1.1 Sexually Transmitted Diseases
The evaluation of fluid specimens for sexually transmitted diseases (STDs) is an important part of a genitourinary exam. STDs can affect both men and women and, as the term implies, they are communicated by intimate sexual contact. In this lesson, we'll review several types of STDs.
|
|
Sexually transmitted diseases were formerly called venereal diseases. This term was derived from the name of Venus, the Roman goddess of love and beauty. |
1.2 Chlamydia
Chlamydia, caused by the bacterium Chlamydia trachomatis, is currently believed to be the most prevalent STD in the
1.3 Chancroid
Chancroid is an STD caused by infection with the bacterium Haemophilus ducreyi. This organism causes one or more painful ulcers on the genitalia and is also associated with inguinal lymphadenitis. The affected lymph nodes may progress toward abscess formation; chancroid can also be treated with antibiotics.
1.4 Gonorrhea
Gonorrhea is a common STD that is caused by gonococci bacteria (see illustration) and results in inflammation of the mucous membranes of the reproductive tract. Indications of the disorder include urethritis, painful urination; a mucopurulent (pus-filled) urethral or vaginal discharge; and itching, burning, or pain around the vaginal or urethral opening. As with chlamydia, many women carry the disease without symptoms.
Diagnosis of gonorrhea is confirmed by a laboratory culture of the urethral or vaginal secretions. The infection is treated with antibiotics.
1.5 Herpes Genitalis
Herpes genitalis is a chronic infection caused by the herpes simplex virus (HSV) and is usually transmitted by sexual contact. Infection with the virus leads to development of fluid-filled lesions and ulcers on the male and female genitals. Additional symptoms include headache, fever, and swelling of the lymph nodes.
There are two types of HSV, Type I and Type II. Genital herpes is usually caused by HSV II. HSV I is more likely to cause cold sores, lesions of the lip.
When present during pregnancy, the HSV II may also be communicated to the fetus or neonate through the placenta and through direct contact with infected tissue at birth. The lesions associated with herpes genitalis often heal spontaneously. Medications are prescribed to suppress the frequency of recurrence, but there is no known cure for herpes infection.
1.6 Syphilis
Syphilis is a sexually transmitted disease caused by a spirochete, a spiral-shaped bacterium. The disease is characterized by distinct stages that mark its progression. The illness can affect any organ system and, because the infecting organism can pass through the placenta, it can cause congenital infection.
The first stage of the disease, primary syphilis, is accompanied by the appearance of a chancre (Fig. A), a red, bloodless, and painless ulcer on the external genitals. Indications of secondary syphilis include cutaneous eruptions (Fig. B), hair loss, swelling of the lymph nodes, and bone and joint pain.
In late stages of the disease, damage to the central nervous and cardiovascular systems may occur, and the disease may lead to death, if not treated. Syphilis is treated with antibiotics.
1.8 Human Papillomavirus (HPV)
Infection by the human papillomavirus (HPV) is referred to in lay terms as genital warts. The term for the wartlike lesion is condyloma acuminatum, often shortened to condyloma. These lesions appear on the external genitalia of both males and females.
HPV is one of the most common sexually transmitted diseases, and there is no cure for it. The lesions can be removed, and treatment for other symptoms may be helpful, but the virus cannot be eliminated from the body. This virus is linked to increased risk of cancer of the reproductive organs, especially to cervical cancer in females.
1.9 HIV and AIDS
The most deadly STD today is infection by the human immunodeficiency virus (HIV), the agent that causes acquired immunodeficiency syndrome (AIDS). Since AIDS was first identified in the early 1980s, more than a million victims of this disease have been identified in the
HIV is a pathogen that is spread by contact with body fluids, including semen, vaginal secretions, and blood. It is the adverse effect of the virus on the cells of the immune system that suppresses the normal immune response and causes the manifestations of AIDS. The infections that occur with AIDS are called opportunistic infections because they occur when certain microorganisms take advantage of the opportunity to invade in the absence of an immune response. Some of the opportunistic infections observed are Pneumocystis carinii pneumonia, Candida albicans infection of mucous membranes, and widely scattered lesions from herpes virus and cytomegalovirus. There is also an increased risk of developing active tuberculosis. Kaposi's sarcoma, a malignancy of pigmented cells of the skin, is a form of cancer that often affects AIDS patients.
At this time, there is no cure for HIV or AIDS, but drugs have been developed that prolong the time required for HIV infection to progress to AIDS.
1.10 Hepatitis B and C
You will recall from the discussion of liver diseases in Module 10 that infections by the hepatitis B virus (HBV) (Fig. A) and the hepatitis C virus (HCV) (Fig. B) are viral diseases transmitted by blood and body fluids. Both may be transmitted during sexual intercourse as well as through contaminated needles and blood products.
The clinical manifestations of all types of hepatitis are similar: jaundice (bile pigment in the blood causing the skin and whites of the eyes to appear yellow), fatigue, abdominal pain, loss of appetite, nausea, vomiting, and diarrhea. Both HBV and HCV have the potential to develop into chronic infections, although the risk is greater with hepatitis C.
1.11 Trichomoniasis
Trichomoniasis is a sexually transmitted disease caused by the single-celled protozoan parasite Trichomonas vaginalis.
Women have signs or symptoms of infection that include a frothy, yellow-green vaginal discharge (as seen in the illustration) with a strong odor. The infection may cause discomfort during intercourse and urination as well as irritation and itching of the genital area. Men may have no symptoms at all or may experience mild urethritis.
Infections can be successfully treated with antiprotozoal medications, drugs that are effective against protozoa.
1.12 Pubic Lice
Pubic lice are tiny parasitic insects. They are sometimes called crab lice, or "crabs," because they are shaped like minute crabs (as the illustration shows). Although they can be transmitted via bed linens or clothing, they do not live long when they are separated from the host. The usual mode of transmission is through sexual contact. The term for infestation by lice is pediculosis.
Pubic lice attach themselves to pubic hair and cause intense itching. They are easily treated with OTC medications and soaps called pediculicides that contain pyrethrin. Prescription medications in the form of lotions that kill pubic lice are also available.
Introduction
In this module, you will learn about the medical terms associated with the muscular and skeletal systems. When you complete this module, you should be familiar with terms that describe the anatomy of these systems and have a good understanding of terms that specify disorders affecting bones, muscles, and joints. You will recognize terms for tests and procedures that are used to diagnose and treat musculoskeletal disorders.
This integrated learning program is intended as a supplement to your text—not as a substitute. Be sure to keep your text available for ready reference.
Objectives
In this module, you will learn to:
- Identify the major bones of the body and write their combining forms.
- Match bones, muscles, and supporting structures with their functions.
- Differentiate the different types of body movements.
- Match types of fractures with their descriptions.
- List and describe the functions of the three types of muscle tissue.
- Write the meanings of the word parts and use them to build and analyze terms.
1.1 Threaded Case Study: Mrs. Nouri
To help us understand how the musculoskeletal system functions, let's meet Mrs. Nouri, who has been seeing her physician from time to time with lower back pain. We'll consider her symptoms as we learn about musculoskeletal system anatomy and physiology.
Within these two systems, muscular and skeletal, the body receives its framework, protection, and support for all its internal organs and a means of achieving both internal and external movement. In addition, on the cellular level, the skeletal system provides storage of the minerals needed for its own growth, development, and repair. Red bone marrow functions in the formation of blood.
1.2 Structure of Bone Tissue
Let's start with the composition and structure of bones; then we will look at the overall skeletal structure.
We can consider each bone a complete organ composed of a specific kind of connective tissue called osseous tissue. Osseous means bony, and the combining form for bone is oste/o.
Osseous tissue is suffused with a rich supply of blood vessels and nerves. If we magnify the osseous tissue we see that it is made up of a combination of bone cells called osteocytes, dense connective tissue strands known as collagen, and intercellular calcium salts. The combining form coll/a means glue.
1.3 Process of Ossification
Bone formation begins in the embryo, and the same process that occurs in the beginning repeats itself over and over again throughout our entire lives.
The bones of the embryo begin as cartilage, which is basically osseous tissue without the calcium salts. The combining form for cartilage is chondr/o.
During fetal development, through a complex chemical process mediated by collagen, the calcium salts and the cartilage cells evolve, creating immature bone cells containing calcium deposits. The deposition of calcium is called ossification and the process of bone formation is referred to as osteogenesis.
1.4 Epiphyseal Line
This bone illustrates the lifelong ossification process. Here we see the long bone of an adolescent. The arrow points to an area of cartilage tissue that is generating new bony tissue as the bone grows. This area can be referred to by any of the following names: the epiphyseal line, the epiphyseal plate, or the growth plate. Whatever you choose to call it, you can see that as cartilage cells at the edges of this plate form new bone, the bone lengthens.
When the bone has achieved its full growth, the epiphyseal plate will calcify and disappear. Calcification means that a deposit of calcium salts hardens the tissue. The combining form for calcium is calci/o. The chemical symbol for the element calcium is Ca.
This is just a glimpse of an area of the bone associated with bone growth and ossification. We will look at the other portions of a typical long bone in a moment. But first, let's have a closer look at the bone cells themselves.
1.5 Osteoblasts
As you can see, there are two kinds of bone cells, or osteocytes. The smaller, immature osteocytes, seen here, are called osteoblasts. We already know that oste/o means bone; combining it with the suffix -blast, which means embryonic form, gives us the name for these immature bone cells—osteoblasts. These are the cells that form the bony tissue that replaces the cartilage. When used as a root, the combining form for an embryonic state is blast/o.
The larger cells seen here are osteoclasts or bone phagocytes.
Pause now to make a prediction. Understanding that osteoblasts form bony tissue, what do you predict these osteoclasts will do?
1.6 Osteoclasts
Osteoclasts reabsorb, or digest, bony tissue inside each bone, thus enlarging the inner cavity. This is not as destructive as it seems. This process prevents the bone from becoming too thick and heavy. You will recall from previous modules that phagocytes are cells that surround, engulf, and ingest other cells or material.
From these descriptions, it is easy to see how the continual tearing down and rebuilding of bony tissue helps keep the body's bone structure strong and in good repair.
1.7 Ossification
Remember that osseous tissue is made up of osteocytes, dense connective tissue strands known as collagen, and calcium salts. How do the calcium salts form?
Osteoblasts produce an enzyme that causes the formation of the major calcium salt, calcium phosphate, the substance that makes bone tissue hard. To accomplish this, the osteoblasts need an adequate intake of calcium, phosphorus, and vitamin D (which helps in calcium transport).
1.10 Types of Bones
There are four basic types of bones in the body. As you can see here, the long bones are found in the legs and arms and the short bones are in the wrists and ankles.
But there are two more types of bone with various locations and functions: flat bones and irregular bones. Flat bones cover and protect soft body parts. These include the shoulder blade, ribs, and pelvic bones (bones found at the lower portion of the trunk, or pelvis; the combining form for pelvis is pelv/i).
Irregular bones are often clustered in groups. The vertebrae that form the spine are a good example.
Sesamoid bones are unusual irregular bones. These small rounded bones are found near certain joints and are encased in tendons. Sesamoid means sesamelike and indicates that these bones are shaped like sesame seeds. The number of sesamoid bones varies from person to person.
|
|
The kneecap, or patella, is the largest of the sesamoid bones. It is the only sesamoid bone that has a specific name and the only one that is numbered among the bones of the body. |
1.11 Long Bone Structure
Now let's look at the key anatomic features of a typical long bone. Each end of the long bone is called the epiphysis. The middle shaft is the diaphysis.
Between the epiphysis and diaphysis, the shaft of the bone flares somewhat. This portion is referred to as the metaphysis.
1.12 Joints
The contact between two bones is called a joint or articulation. The combining forms arthr/o and articul/o mean joint. Articular means pertaining to a joint.
The surfaces of bones that form moving joints are protected from direct bone-to-bone contact by cushions of articular cartilage that are slick, smooth, and very tough.
A thin layer of tissue called synovial membrane, or synovium, lines the articular capsule surrounding a freely movable joint. The combining form for synovium is synov/o. Synovial membrane secretes synovia, a viscous fluid that lubricates the joint, also called synovial fluid. Synovial means pertaining to synovium or to synovial fluid.
A fibrous, fluid-filled sac called a bursa cushions some joints. Bursae are found in regions where muscles or tendons rub against other muscles, tendons, or bones, such as the knee, shoulder, and hip. The bursae function in two ways: lubricating points of friction and dissipating force by distributing it through a fluid medium. In the hand and foot, the bursa assumes a tubular form called the synovial sheath, which encloses the tendons along their entire length.
1.13 Tendons and Ligaments
As we will see in the next lesson, bones are moved by the action of muscles. Muscles are attached to bones or cartilage by means of fibrous cords called tendons (Fig. A). The term tendon is represented by the combining forms ten/o, tend/o, and tendin/o.
Tendons are sometimes confused with ligaments, bands of fibrous tissue that connect bones to each other or to cartilage. Ligaments serve to strengthen and stabilize joints (Fig. B).
1.14 Layers of Bone
Now let's examine the layers of the bone from the outside in. The outermost layer is the tough, fibrous periosteum, which comprises the outermost surface of the long bones, except at the ends of the epiphyses. Just beneath its surface is a layer of osteoblasts, which deposit calcium phosphate in the bony tissue. Cartilage has a similar outer covering called perichondrium, a fibrous connective tissue that closely wraps all cartilage except the cartilage in moving joints, which is covered instead by a synovial membrane.
Just below the periosteum layer of bone is the hardest, densest layer, the strong compact bone called the cortex. This layer contains blood vessels that deliver oxygen and nutrients to the bone while removing waste products, such as carbon dioxide.
The inner layer consists of cancellous bone, a spongy, porous layer that forms a latticework of separated bony fibers called trabeculae.
These three layers form a hollow tube that surrounds the medullary cavity, which contains yellow bone marrow, made up mostly of fat cells.
1.15 Bone Processes and Indentations
Bones have unusual shapes that serve their individual functions. With the exception of paired bones that are mirror images of each other, all are unique because they have different bone markings. Bone markings are the prominences and indentations that are significant features of the bone.
For example, this illustration shows a vertebra, a bone of the spine, with four different processes identified. A process is a prominence of the bone that extends beyond its body or main part.
In this example, the superior and inferior articular processes form joints with the vertebrae above and below. The transverse and spinal processes are attachments for tendons. Tendons are fibrous cords that attach muscles to bones.
An indentation or depression in a bone is often called a fossa. Indentations may serve to fit together with another bone, to allow movement, or to provide a suitable place for a soft tissue feature such as a gland, nerve, or blood vessel.
1.16 More Bone Markings
Depending on their sizes and shapes, bone markings are identified with various terms.
Processes that are sites of muscle, tendon, and ligament attachment:
Tuberosity: Large rounded projection that may be roughened
Crest: Narrow, usually prominent, ridge of bone
Trochanter: Very large, blunt, irregularly shaped process
Line: Narrow ridge of bone that is less prominent than a crest
Tubercle: Small rounded process
Epicondyle: Raised area on or above a condyle
Spine: Sharp, slender, often pointed process
Processes that help to form joints:
Head: Bony expansion carried on a narrow neck
Facet: Smooth, nearly flat articular surface
Condyle: Rounded articular projection
Ramus: Armlike bar of a bone
Depressions and openings that allow blood vessels and nerves to pass:
Meatus: Canal-like passageway
Sinus: Cavity within a bone filled with air and lined with mucous membrane
Fossa: Shallow, basinlike depression in a bone, often serving as an articular surface
Groove: Furrow
Fissure: Narrow, slitlike opening
Foramen: Round or oval opening through a bone
2.1 Threaded Case Study: Mrs. Nouri
Remember Mrs. Nouri? Unfortunately, she has begun to experience pain in her joints when exercising. Her physician is working now to pinpoint the specific areas of her bone and joint pain. We will be checking Mrs. Nouri's progress as we learn about the anatomy and physiology of the musculoskeletal system.
2.2 Axial Skeleton
The skeleton is divided into two basic parts: the axial skeleton, consisting of the skull, spinal column, ribs, and sternum, and the appendicular skeleton, made up of the upper and lower extremities plus the shoulder girdle and the pelvic girdle.
We will begin our study of the skeletal system with the axial skeleton.
2.3 Cranium
The eight major bones of the skull make up the cranium, or brain case. The combining form that refers to the cranium is crani/o. The term cranial means pertaining to the cranium.
The frontal bone forms the forehead and a roof over the eye sockets, which are called the orbits. Two large parietal bones, one on each side of the head, form the roof and upper sides of the cranium.
Below this, the sphenoid bone forms part of the floor and walls of these eye sockets, extending to form part of the base of the skull as well. A depression in its superior surface, the sella turcica, holds the pituitary gland. The nearby ethmoid bone forms part of the nose, orbit, and floor of the cranium.
2.4 Bones of the Cranium
Beneath the parietal bones, the temporal bones form the lower sidewalls of the skull, the part that contains the ears. You will note in the illustration that the temporal bone has two significant processes: the mastoid process behind the ear and the styloid process, a muscle attachment behind the jaw within the neck. The temporal bone also has a fossa that articulates with the lower jaw.
The occipital bone forms the back of the skull and the posterior portion of its base. The large opening in the base of the occipital bone is called the foramen magnum, which literally means big hole. It is the passageway between the brain and the spinal cord.
2.5 Facial Bones
The remaining bones of the head, with six notable exceptions, are classified as facial bones.
At the inner aspects of the eye sockets are a pair of lacrimal bones that make up part of the orbits. The combining form lacrim/o means tears, and lacrimal means pertaining to tears. The tear glands and ducts are adjacent to the lacrimal bones.
Between the orbits are the two slender nasal bones, which form the bridge of the nose. The thin, flat vomer bone articulates with the ethmoid bone and forms a base for the nasal septum, the cartilage that separates the nasal cavities. Within the nasal cavities are three pairs of thin bones called the superior, middle, and inferior nasal conchae (sing., concha).
The palatine bone forms the hard palate, the roof of the mouth. It is situated at the back part of the nasal cavity between the upper jawbone and the sphenoid. It contributes to the walls of three cavities: the floor of the nasal cavity, the roof of the mouth, and the floor of the orbit.
The cheek bones are called zygomatic bones or zygomas.
2.6 Jaw Bones
The paired bones that form the upper jaw are called the maxillae; in the adult they fuse to form a single bone, the maxilla. The lower jawbone is called the mandible. Both of these facial bones have alveolar processes that contain sockets for holding the teeth. The combining form that means maxilla is maxill/o and that for the mandible is mandibul/o.
The superior processes on either side of the mandible, called the condyles, articulate with the temporal bones bilaterally to form the temporomandibular joints (TMJ). These joints permit opening and closing of the mouth.
2.7 Auditory Ossicles
Earlier we mentioned that there were six bones in the head that are not classified as part of the cranium or the face. Three tiny bones within the middle ear cavity of each temporal bone are called the auditory ossicles. The term ossicle means small bone. The ear ossicles are named for their shapes: malleus, which means mallet or hammer; incus, which means anvil; and stapes, which is Latin for stirrup. These bones transmit sound vibrations from the eardrum to the inner ear.
2.9 Vertebra
The spine, or spinal column, begins at the base of the skull and ends with the tailbone. The combining forms spin/o and rachi/o mean spine.
The spine consists of a series of bones called vertebrae (sing., vertebra). The combining forms that mean vertebra are spondyl/o and vertebr/o. Vertebral means pertaining to a vertebra. Pads of cartilage called intervertebral disks separate the bodies, or main portions of the vertebrae, from each other. The prefix inter- means between, and intervertebral means between any two adjacent vertebrae.
A typical vertebra has an anterior body and a posterior vertebral arch. This arch consists of the pedicles, which attach to the body on either side, and the laminae (sing., lamina), the most posterior portions of the arch that join together in the midline posteriorly.
The opening between the body and the posterior arch is the vertebral foramen or neural canal, through which the spinal cord passes.
The transverse processes extend laterally from the junctions between the pedicles and the laminae, and the articular process extends superiorly and inferiorly from the same area. The spinous process extends posteriorly from the junction of the laminae.
2.10 Divisions of the Spine
The spine is naturally divided into five distinct sections. The first seven vertebrae make up the section called the cervical spine, the bony structure of the neck. These vertebrae are numbered C1 through C7, starting at the top. These delicate bones are responsible for supporting the head and participating in its intricate movements from side to side and up and down. The joints of the cervical spine are the most flexible joints in the vertebral column. The combining form cervic/o means neck, and cervical means pertaining to the neck. C1 and C2 are atypical vertebrae and are called the atlas and the axis, respectively.
The thoracic vertebrae are the ones that articulate with the 12 pairs of ribs; they are numbered T1 through T12. The thoracic spine supports the upper part of the torso. You will recall that thorac/o means chest and the term thoracic means pertaining to the chest.
The lumbar vertebrae, numbered L1 through L5, form the section of the spine that in lay terms is called the lower back. These are the strongest and largest bones of the spine. The combining form lumb/o means loins or lumbar area, and lumbar means pertaining to the loins or to the lumbar portion of the spine. Thoracolumbar means pertaining to both the thoracic and lumbar regions.
Near the bottom of the spine, we find the curved, triangular sacrum and the coccyx, or tailbone. The combining form for sacrum is sacr/o and for coccyx, it's coccyg/o. Thus, something that pertains to the sacrum is sacral and something pertaining to the coccyx is referred to as coccygeal. At birth, the sacrum consists of five vertebrae and the coccyx consists of four. At puberty, the sacral segments begin to fuse, eventually forming a single, solid bone between the ages of 20 and 30. The coccygeal segments tend to fuse as well, although in some individuals they do not fuse completely.
2.11 Thoracic Cage: Sternum
Now let's examine the bony thorax, also called the thoracic cage, or rib cage. Recall that the term thorax means chest, or the portion of the body between the neck and the diaphragm; its combining form is thorac/o.
The thoracic cage is made up of the thoracic vertebrae, the sternum, and the ribs. It serves to protect the heart and lungs.
The medical term for the breastbone is sternum; its combining form is stern/o. It forms the middle of the anterior rib cage and consists of three parts. The upper portion articulates with the collar bones and is called the manubrium; the long central portion is called the body or gladiolus; and the lower potion is called the xiphoid process. The combining form for xiphoid is xiph/o. Both gladiolus and xiphoid are derived from roots that mean sword.
Because the sternum is an anterior structure that is easily palpated, it is often used as a reference point for other locations or structures. For example, retrosternal means behind the sternum, substernal and infrasternal mean below the sternum, and suprasternal means above the sternum.
2.12 Ribs
The twelve pairs of ribs are numbered from the top down and all are attached to the vertebral column posteriorly. The combining form that means rib is cost/o, and costal means pertaining to one or more ribs.
Ribs 1 through 7 are joined to the sternum in the front by cartilage and are called true ribs. Ribs 8 through 10 do not join to the sternum directly; instead, they are joined by cartilage to the 7th rib. These are called false ribs. Ribs 11 and 12 are false ribs, too, but they are not attached anteriorly at all; thus, they are also called floating ribs.
Recall that the combining form for cartilage is chondr/o; thus, chondrocostal and costochondral both mean pertaining to both rib and cartilage. For example, the chondrocostal junction is the place where the rib and its associated cartilage come together.
2.14 Appendicular Skeleton
Now let's turn our attention to the appendicular skeleton, which you may remember consists of the upper and lower limbs or extremities as well as the pelvic girdle and shoulder girdle. The appendicular skeleton makes body movement possible and helps to protect internal organs.
2.15 Shoulder Girdle
Let's start with the shoulder girdle. This bilateral structure consists of two bones: the clavicle, or collar bone, and the scapula, known in lay terms as the shoulder blade. The clavicle connects the sternum to the scapula.
The combining form for clavicle is clavicul/o, and clavicular means pertaining to the clavicle. Scapul/o means scapula, and scapular means pertaining to the scapula.
A large process on the superior aspect of the scapula is called the acromion. It forms a joint with the distal clavicle called the acromioclavicular (AC) joint.
2.16 Bones of the Arm
Here we can see the full length of the arm and hand. The upper arm bone is called the humerus. Its combining form is humer/o, and humeral means pertaining to the humerus. The humerus forms the shoulder joint at its proximal end where it articulates with the glenoid fossa of the scapula; at its distal end, it articulates with the bones of the forearm to form the elbow joint.
The forearm consists of two long bones, the ulna and the radius. The ulna is longer and more slender and is located on the medial aspect. Its combining form is uln/o, and ulnar means pertaining to the ulna. The radius is thicker and shorter and attached on the thumb side, the lateral aspect. Its combining form is radi/o; radial means pertaining to the radius.
Note in the illustration that the proximal ulna terminates in the olecranon process, called in lay terms the funny bone, which fits into the olecranon fossa of the humerus when the arm is extended. The distal ends of both forearm bones have bony prominences called styloid processes.
2.17 Bones of the Wrist and Hand
The wrist and hand bones are small and numerous. The wrist is also called the carpus. Its combining form is carp/o. The carpus consists of eight carpal bones or carpals. As you could surely guess, carpal means pertaining to the wrist.
The bones of the palm of the hand are called metacarpals. There are five, numbered 1 to 5, starting on the thumb side. They connect the wrist to the fingers.
The finger bones themselves are called phalanges. Those that articulate with the metacarpals are the proximal phalanges; those nearest the tips of the fingers are the distal phalanges. All but the thumbs have middle or medial phalanges as well.
The singular form of the term phalanges is phalanx. The combining form for phalanx is phalang/o, and phalangeal means pertaining to one or more phalanges.
2.19 Pelvic Girdle
Now let's move to the lower appendicular skeleton.
At the bottom of the vertebral column is the lower section of the appendicular skeleton: the pelvic girdle. In lay terms it is sometimes called the pelvic bone or the hips. This structure protects internal organs and supports the lower extremities.
The pelvic girdle consists of the right and left innominate bones, attached posteriorly to the sacrum. Each innominate bone is actually three bones: the ilium (ili/o), the upper, blade-shaped section that articulates with the sacrum to form the sacroiliac joint; the lower, posterior part called the ischium (ischi/o); and the pubis (pub/o), also called the pubic bone. The two pubic bones join anteriorly at the midline to form the cartilaginous joint called the symphysis pubis. The plural forms for ilium, ischium, and pubis are ilia, ischia, and pubes, respectively.
Two roots are combined to form the term ischiopubic, which means pertaining to both the ischium and the pubis. Ischial means pertaining to the ischium alone. Bone pain in the ischium is called ischialgia or ischiodynia.
The ilium, ischium, and pubis all come together to form the acetabulum, the socket that articulates with the head of the femur to form the hip joint.
|
|
The round depression called the acetabulum gets its name from its similarity to the round cup the Romans used for holding vinegar or acetum. |
2.20 Bones of the Lower Extremity
The femur, or thigh bone, is the longest bone in the body. The rounded process at its proximal end is called the head and fits perfectly into its articulation with the acetabulum. The combining form that means femur is femor/o, and femoral means pertaining to the femur.
The leg, sometimes called the lower leg, is that part between the knee and the ankle. Two bones make up the leg: the tibia, or shin bone, and the fibula, which is smaller and located lateral to the tibia. The articulation between the distal femur and the proximal tibia forms the knee joint. The proximal fibula articulates with the proximal tibia and is not a part of the knee joint. The combining forms for tibia and fibula are tibi/o and fibul/o, respectively. Tibial means pertaining to the tibia, and fibular means pertaining to the fibula.
You will recall from earlier in this module that the kneecap is actually a large sesamoid bone called the patella. Its combining form is patell/o. The patella is easily felt, a flat bone at the front of the knee. It is surrounded and held in place by tendons. The term that means pertaining to the patella is patellar.
2.21 Ankle and Foot Bones
The ankle joint is made up of the tibia, the fibula, and the talus, the most superior of the tarsal bones.
The term tarsus means ankle, and its combining form is tars/o. There are seven tarsal bones, or tarsals; they are sometimes referred to as ankle bones, but the talus is the only one that is actually a part of the ankle joint.
The largest of the tarsal bones is the calcaneus, also known as the heel bone. Its combining form is calcane/o, and calcaneal means pertaining to the heel.
Distal to the tarsals are the bones of the forefoot, called the metatarsals. As with the metacarpals of the hand, there are five metatarsals, numbered 1 through 5, beginning medially. They extend from the tarsals to the proximal phalanges of the toes.
The term for the first or great toe is hallux. Similar to the thumb of the hand, the great toe is the only toe to not have a middle phalanx. It has only proximal and distal phalanges; the other toes all consist of three phalanges: proximal, middle, and distal.
3.1 Skeletal Muscle
Muscles are tissues that produce movement; they are composed of cells and fibers with the ability to contract. Two combining forms represent muscle: muscul/o and my/o.
Myoblasts are embryonic cells that mature to become part of a muscle fiber.
Most muscles are striated muscles, named for the striations, or stripes, that are apparent in this tissue under a microscope. You can see the striations in the illustration at the upper left. The cells that make up these muscles are fibers with dark and light bands, or fibrils, in their cytoplasm.
Striated muscles are called skeletal muscles because most of them are attached to the bones and work with the skeleton to produce movement. These muscles are also responsible for moving all of the face and the eyes.
Striated muscles also have a third name: voluntary muscles. This term comes from the fact that these muscles are under our conscious and voluntary control.
The combining form that means striated muscle is rhabdomy/o.
Striated muscles are enveloped and separated by a fibrous tissue called fascia that contains the muscle's blood, lymph, and nerve supply. The combining form that means fascia is fasci/o.
3.2 Smooth Muscle
The second type of muscle is smooth muscle. Smooth muscle operates to cause movement of internal organs, blood vessels, and glandular ducts and is controlled or self-regulated by the autonomic nervous system. Auto- means self. For this reason, they are also called involuntary or visceral muscles. Visceral means pertaining to one or more abdominal organs.
Looking closer, you can see why these are called smooth muscles. These cells have no dark and light fibrils in their cytoplasm. Instead of being arranged in bundles like skeletal muscles, they form sheets of fibers that wrap around tubes and vessels.
3.3 Cardiac Muscle
The third type of muscle has characteristics of each of the other types. Cardiac muscle, found in the heart, is striated like skeletal muscle tissue but similar in action to smooth muscle in that it cannot be consciously controlled. You will recall from Module 8 that heart muscle tissue is called myocardium.
Let's look at cardiac muscle cells closely. In the microscopic illustration, you can see that cardiac muscle fibers are branching fibers.
|
|
Muscles alone make up nearly half of the human body's weight. |
3.5 Flexion/Extension (animation)
The bending motion seen here and in the animation is called flexion, and extension takes place as the limb straightens.
3.6 Abduction/Adduction (animation)
Abduction is movement away from the midline of the body. The prefix ab- means away from, and the combining form duct/o means to lead or to carry.
Moving the limb back toward the midline of the body is called adduction. The prefix ad- means toward.
3.7 Circumduction and Rotation
Perhaps you recall from Module 12 that the prefix circum- means around or in a circle. Thus, the term circumduction means moving in a circle (Fig. A). The joints that perform this movement include the shoulder, the wrist, and the hip.
Rotation is a circular movement in one plane. It is a rather smooth combination of several skeletal muscle movements that turns the body part in a circular path. Turning the head from left to right is an example of rotation (Fig. B).
3.8 Pronation/Supination (animation)
You will recall from Module 6 that when someone is lying prone, this means face down. Thus, placing the palm down is called pronation and turning the palm so that it faces up is called supination. Skeletal muscles can move some joints in multiple directions in one smooth arc when required.
3.9 Inversion/Eversion
The suffixes -vert and -version mean to turn and turning, respectively. Inversion, therefore, means turning inward, and eversion means turning outward. These terms are commonly applied to the side-to-side movements of the ankle joint.
1.1 Myasthenia Gravis
Let's begin our coverage of disorders of the musculoskeletal system by reviewing a few key types of muscular disorders and syndromes.
Recall that the two combining forms that represent muscle are muscul/o and my/o. Thus, any condition adversely affecting the muscle is referred to as a myopathy.
Myalgia is any sort of pain in a muscle or muscles. This term combines my/o with the suffix -algia, meaning pain. Another word for muscle pain is myodynia, using the other suffix that means pain, -dynia.
Abnormal softening (-malacia) of a muscle is called myomalacia, and destruction (-lysis) of muscle tissue is called myolysis. Myofibrosis is a condition characterized by the replacement of muscle tissue by fibrous tissue; this process occurs as a result of injury or disease affecting the muscle.
The suffix -asthenia means weakness, so muscle weakness is myasthenia. Myasthenia gravis (MG) is the most common primary disorder of neuromuscular transmission; that is, it affects the nerve signals that control muscle activity. MG is a chronic autoimmune disorder that results in progressive skeletal muscle weakness. The usual cause is an acquired immunological abnormality, but some cases result from genetic abnormalities at the neuromuscular junction. A wide range of potentially effective treatments is available. Sometimes MG affects the muscles of the eyes, as illustrated here.
You will recall from Module 7 that autoimmune disorders result when the body produces an immune response against itself. The prefix auto- means self. An autoimmune disease is an altered function of the body's immune system that results in the production of antibodies that act against one's own cells. Several significant diseases of the musculoskeletal system are classified as autoimmune conditions.
1.2 Polymyositis
Polymyositis is a chronic inflammatory myopathy that is also believed to be an autoimmune disorder. In addition to symmetrical muscle weakness with pain, the patient typically exhibits a rash over the face and eyes as well as on the limbs. Muscle fibers undergo necrosis and are surrounded by or infiltrated with lymphocytes and macrophages. This photomicrograph shows muscle tissue invaded by lymphocytes.
Myocellulitis is a term that refers to any inflammation of both cellular (cellul/o) tissue and muscle, usually as a result of an infectious process.
1.3 Polymyalgia Rheumatica
Polymyalgia means pain in many muscles, and rheumatica suggests that the condition is one of the autoimmune diseases. Polymyalgia rheumatica (PMR) is believed to be caused when the immune system attacks the arteries that supply the muscles. Although this condition may affect any muscle group, it is primarily associated with the muscles of the hip and shoulder regions. It typically has a sudden onset and may resolve spontaneously. It is treated with corticosteroid drugs.
1.4 Fibromyalgia
Some muscle symptoms and syndromes are caused by problems outside the muscle itself. One of the most common of these secondary muscle syndromes is fibromyalgia.
Diffuse pain and areas called tender points that are increasingly sensitive to touch characterize this condition. Fatigue and sleeping problems are common as well.
Fibromyalgia is frequently misunderstood. Because the symptoms are vague, they are sometimes misdiagnosed as chronic fatigue syndrome. The most reliable indicator is a mapping of tender points, marked in this diagram.
1.5 Muscular Dystrophy
Some muscle disorders are inherited, chiefly the muscular dystrophies. The word dystrophy comes from the prefix dys-, meaning bad or difficult, and the suffix -trophy, meaning nutrition. You may recall that the combining form troph/o also means nutrition.
Dystrophy is characterized by progressive weakness and degeneration of muscle fibers. This generally begins soon after birth. For example, the child in this photograph is affected with Duchenne dystrophy, the most common form. Note the weakness and hypotonia of the shoulder girdle musculature. Hypotonia means decreased muscle tone.
1.6 Musculoskeletal Soft Tissue Trauma
Trauma to the musculoskeletal system that does not injure the bone may be classified as a sprain or a strain.
A sprain is a stretching or tearing of a ligament. For example, twisting one's ankle may cause a sprain.
The term strain refers to the stretching or tearing of a muscle (as the illustration demonstrates). When the muscle sheath is ruptured and the muscle protrudes from it, this herniation is called a myocele.
1.7 Tendinitis
Recall that a tendon is a band of fibrous tissue that connects a muscle to a bone. Tendons can also be injured through inflammation or trauma.
Inflammation of a tendon is called tendinitis. Pain in tendons is called tenodynia or tenalgia.
Irritation and inflammation of a tendon and its synovial sheath may be caused by overuse. The inflamed sheath can fill up with fluid, causing pain. Sometimes this swollen sheath causes a bump under the skin, called a ganglion or ganglion cyst. The most common site for ganglion cysts is the back of the wrist, but they can also occur on the fingers and about the shoulder, hip, elbow, ankle, knee, and foot. They can increase in size when the tissue is irritated and can disappear spontaneously. These masses or cysts sometimes appear to grow, but they are not tumors.
1.8 Inflammation of Joint Soft Tissues
You will recall that a fibrous, fluid-filled sac called a bursa cushions some joints, such as the hip, knee, and shoulder. Joint injury or irritation may lead to inflammation and oversecretion of fluid with enlargement of the bursa, a condition known as bursitis. While bursitis may affect several different joints, it is most common in the shoulder. Bursitis is sometimes associated with a bursolith, a calcification or stone (-lith) in the bursa, as shown in the accompanying figure.
Inflammation of the synovial membrane is a condition called synovitis. The condition commonly affects the knee joint, but many other joints are vulnerable to it as well. When the inflammation involves both the synovium and a tendon, it is called tenosynovitis; DeQuervain's disease is the term for a common type of tenosynovitis that occurs in the wrist.
Excessive repetition of small movements causes trauma to the soft tissues of joints, called repetitive motion or repetitive stress injury. Such injuries are becoming increasingly common in the workplace. Bursitis, tendinitis, synovitis, and tenosynovitis all may be caused by irritation from repetitive motion trauma.
1.9 Carpal Tunnel Syndrome
Carpal tunnel syndrome is a common example of a repetitive stress injury; it is often attributed to keyboard use. In this condition, the median nerve is squeezed or constricted by a wrist ligament as it passes between that ligament and the bones and tendons of the wrist. Both numbness and burning pain may occur in the fingers and hands, sometimes extending all the way to the elbow.
1.10 Rotator Cuff Injuries
The rotator cuff is a group of four muscles that lift the shoulder up over the head and also rotate it toward and away from the body. Tears, tendonitis, impingement, bursitis, and strains frequently injure this group of muscles. There are three general types of rotator cuff injury:
Rotator cuff tendonitis is also known as impingement syndrome or shoulder bursitis. It occurs most often in people over 30 years of age, causing weakness and a limited range of motion (ROM).
A rotator cuff tear (indicated by the arrow on the accompanying radiograph) can occur with sudden trauma, as when lifting something too heavy, but it more often occurs when tendonitis in the rotator cuff gets so bad that it wears a hole through the rotator cuff tendon. Since the tendon connects the rotator cuff muscle to the humerus, shoulder weakness results.
Instability impingement occurs in younger persons, typically 15-30 years old. In this condition, the rotator cuff becomes irritated because the shoulder is loose in the socket. This often happens in swimmers, baseball pitchers, and other throwing athletes.
1.12 Terms for Abnormalities of Cartilage and Ribs
By adding familiar suffixes to the combining form chondr/o, we can create many medical terms that relate to cartilage. For example, the general term for disease of cartilage is chondropathy.
When pain originates within cartilage, it is referred to as chondral pain, chondrodynia, or chondralgia. If the cartilage is inflamed, the condition is called chondritis. A tumor arising from cartilage is called a chondroma (as seen in the illustration).
Softening of cartilage is termed chondromalacia, and the term for destruction of the cartilage is chondrolysis.
In the same manner that we formed terms relating to cartilage, we can also create terms related to ribs, using the combining form cost/o, which means rib or ribs. For example, costal means pertaining to a rib and costalgia means pain in a rib.
Chondrocostal means pertaining to both cartilage and rib. For example, the chondrocostal junction is the point where the rib cartilage joins the rib.
1.13 Calcipenia
Let's consider now some of the more common disorders of the bones and joints.
Calcipenia is the term for a deficiency of calcium. This word is formed by combining calci/o, which means calcium, with the suffix -penia, which means deficiency.
A deficiency of calcium causes a decrease in the density of the bone. Other terms for decreased bone density are osteopenia and osteoporosis. Loss of bone density causes the bone to be more vulnerable to fracture.
Vitamin D is essential for the proper utilization of calcium to make bone. A deficiency of this essential vitamin causes the bone to become soft. This condition of soft bone is called osteomalacia.
1.14 Spinal Curvatures
Seen from the side, the spine has normal curvatures. When the convexity (bowing) of the curve is anterior, the curve is called a lordosis (Fig. A) or lordotic curve. When the convexity is posterior, the curve is called a kyphosis (Fig. B) or kyphotic curve. Lordosis is normally found in the cervical and lumbar regions; kyphosis is typical of the thoracic spine. The terms lordosis and kyphosis may also be used to refer to abnormal exaggeration of these curves. For example, lumbar lordosis or hyperlordosis is the condition commonly referred to as sway back. Abnormal exaggeration of the thoracic curvature, kyphosis or hyperkyphosis, in lay terms is known as hump back. Kyphosis that increases with advanced age is caused by collapse of thoracic vertebrae as a result of osteoporosis.
Seen from the front, the spine is normally straight. Curvature toward one or both sides is an abnormal condition called scoliosis. If, in addition, the spine is twisted, the condition is called rotoscoliosis.
1.15 Fractures and Dislocations
Common musculoskeletal injuries include sprains, strains, dislocations, and fractures.
The trauma of a broken bone is called a fracture, abbreviated fx. Fractures may be categorized according to whether or not the broken end of a fragment protrudes through the skin. If so, it is called a compound fracture or open fracture; if not, it is designated as a simple fracture even though it may be quite complicated.
Various types of simple fractures are illustrated here. A transverse fracture is a single break across the axis of a long bone. An oblique fracture is similar to a transverse fracture except that the fracture line is diagonal. A greenstick fracture involves the cortex on one side of the bone but not the other. These fractures are most common in children because their bones are more flexible than those of adults. Spiral fractures are common in large long bones such as the tibia; they involve a fracture line that winds around the bone. A comminuted fracture is one with a number of fragments. It may be caused by a crushing injury. An avulsion fracture is one in which a small fragment of bone is pulled away by stress on a tendon.
A displaced fracture is one in which the fragments are not in normal alignment. This term may be applied in addition to a descriptive term for the type of fracture. For example, a fracture may be both transverse and displaced; it could also be compound.
These are the general categories of fracture types. There are many additional terms for specific types of fractures of specific bones.
A dislocation is a displacement of a bone from its normal position within a joint. Dislocations are often associated with injuries to both ligaments and muscles.
1.16 Congenital Abnormalities
Some congenital abnormalities are called neural tube defects because they occur as the result of incomplete closure of the dorsal cavity during the embryonic stage of development. A congenital fissure (split or cleft) is indicated by the suffix -schisis.
A congenital fissure of the skull (crani/o) is called cranioschisis. Rachischisis is a congenital fissure of the vertebral column or spine. You will recall that the combining forms rachi/o and spin/o mean spine. This spinal fissure is also known as spina bifida (as seen in the illustration).
A split or fissure can also occur in the sternum, where it is referred to as a sternoschisis. Aggravated, this condition can cause pain, or sternalgia.
1.17 Anomalies
An anomaly is a congenital abnormality or irregularity that is not necessarily a disease or pathologic condition. Examples of anomalies include excess ribs, sometimes attached to the seventh cervical vertebra and sometimes attached to the first lumbar vertebra. Some individuals have an anomalous vertebra, such as a sixth lumbar.
The combining form dactyl/o means digit, finger or toe. Polydactyly (Fig. A) literally means many digits and is the term for the anomaly of having excess digits, that is, more than five fingers per hand or toes per foot. Syndactyly (Fig B.), on the other hand, refers to a failure of differentiation in which the fingers fail to separate into individual appendages. The prefix syn- means together or with.
1.18 Systemic Lupus Erythematosus (SLE)
In systemic lupus erythematosus, or SLE, the collagen in connective tissue throughout the body becomes chronically inflamed, affecting tendons, ligaments, bones, and cartilage all over the body. In addition to affecting the joints, SLE spreads to the skin, kidneys, nervous system, heart, and lungs.
Key symptoms include a red, scaly rash polyarthralgia, pyrexia (fever), and malaise.
When the suffix -algia, meaning pain, is added to arthr/o, which means joint, the result is arthralgia, or joint pain. When the prefix poly-, which means many, is also added, the resulting term, polyarthralgia, means many painful joints.
SLE is a chronic autoimmune disease that is not curable but can be manageable for a very long time with corticosteroid drugs.
1.19 Osteitis
Bones also are subject to inflammatory disease, which may take many different forms. The suffix -itis means inflammation, so any inflammation of the bone can be called osteitis. More specific terms for these conditions may include the name of the involved bone; for example, inflammation of the maxilla is called maxillitis, and inflammation of the calcaneus is called calcaneitis.
Other terms are derived from the words for the specific tissues that are inflamed. Osteochondritis is inflammation of both the bone and cartilage. When inflammation involves the joint cartilage only, the condition is referred to as arthrochondritis.
Similarly, an infectious inflammatory disease of the bone and bone marrow (myel/o) is called osteomyelitis. If treatment for acute osteomyelitis is not completely successful, low-grade chronic osteomyelitis develops with intermittent bone pain, tenderness, and sinus drainage over a period of many years. Eventually, the body encases the infected bone with a supporting osseous structure, as seen in the illustration.
1.20 Rheumatoid Arthritis
In addition to SLE, there are a number of other inflammatory diseases of the joints. Many of these fall under the umbrella title of arthritis. Again, we see the combining form arthr/o, which means joint; the suffix -itis means inflammation. Adding the prefix poly- creates polyarthritis, meaning inflammation of several joints. We will look at several forms of arthritis now.
Note the enlarged joints in this illustration. These deformities are evidence of rheumatoid arthritis, abbreviated RA. RA is a painful, chronic inflammation of the joints. This disease is characterized by an autoimmune reaction against the joint tissues, especially the synovial membrane. The inflamed synovial membranes thicken and damage the articular cartilage. This makes movement difficult and painful. When the fibrous tissue that forms in response to the inflammation calcifies, it forms a bony ankylosis, or union, at the joint and then no movement is possible at all. These swollen, painful joints can be accompanied by pyrexia (fever).
Rheumatoid arthritis is diagnosed by its characteristic appearance on x-rays, shown here, and by a blood test that shows the presence of an antibody called the rheumatoid factor, RF.
1.21 Ankylosing Spondylitis
The general term for disease of joints is arthropathy. Recall that spondyl/o means vertebra. Thus, the general term for disease of the intervertebral joints is spondylarthropathy, also spelled spondyloarthropathy.
The chronic, progressive arthritis of the spine seen in this illustration is called ankylosing spondylitis. Similar to rheumatoid arthritis, it is an autoimmune disease that causes bilateral hardening, or sclerosis, of the joints, particularly the intervertebral and sacroiliac joints.
Breaking down this term, we see that ankyl/o means stiff. Thus, ankylosing spondylitis is inflammation of the spine marked by stiffening of the spinal joints and ligaments. In its advanced stages, this disease causes fusing of the spinal joints and is called bamboo spine.
1.22 Gouty Arthritis
Gout is a systemic condition characterized by increased uric acid levels in the blood. The abbreviation for uric acid is UA. The laboratory blood tests to measure the level of uric acid is called a UA test and provides the definitive means of diagnosing gout.
This patient's gouty arthritis is caused by the accumulation of uric acid in the joints and the soft tissues near the joints. These uric acid salts can destroy articular cartilage and damage the synovial membrane. Chronic gout that leads to deformities of the joints results from a defect in metabolism that causes elevated uric acid levels in the blood.
An acute attack of gout may be due to excessive intake of foods like red meat, red wine, and fermented cheeses, all of which are rich in uric acid. This condition most frequently affects the big toe and is extremely painful. The term for this specific aspect of gout is podagra.
1.23 Osteoarthritis
Osteoarthritis is the most common form of arthritis in the aged population. Osteoarthritis is caused by wear and tear on the joints. It is the result of progressive degeneration, with a loss of articular cartilage and narrowing of the joint space. Hypertrophy (abnormal enlargement) of bone at each joint surface is typical in advanced osteoarthritis. Such hypertrophy often takes the form of a bony outgrowth called a bone spur or osteophyte.
Because it is caused by progressive wear and tear, this condition is also known as degenerative joint disease (DJD). Although it often affects the hips and knees, it can strike any joint, including intervertebral joints and joints of the hands.
1.24 Lyme Disease
Another arthritis-related condition is the hikers' and campers' enemy, Lyme disease.
Lyme disease is the most common vectorborne disease in the
Symptoms include severe arthritis, myalgia, and malaise.
Delayed treatment may result in cardiopathy and neurologic symptoms. It can become chronic if untreated, but even after several years, it can usually be treated successfully with antibiotics. Too long a delay in treatment may result in irreversible joint damage.
1.25 Threaded Case Study: Sciatica (animation)
In Mrs. Nouri's case, her pain originates in the lower back but radiates down her leg (see the animation). This symptom is called sciatica because it follows the course of the sciatic nerve. Together with her other symptoms, this strongly suggests a herniated disk.
Although no diagnosis has been made at this point, let's have a closer look at what that would mean.
1.26 Threaded Case Study: Herniated Disk
You have probably heard someone talk about a slipped disk. This condition is actually a herniated disk, the rupture of the outer fibrous membrane of the disk that results in the protrusion of the softer tissue from inside the disk, which is called the nucleus pulposus. Another term for this condition is herniated nucleus pulposus (HNP).
This condition can cause excruciating pain as a result of pressure on spinal nerves by the protruding disk.
This is characteristic of what our patient, Mrs. Nouri, is experiencing.
1.27 Neoplastic Diseases of the Musculoskeletal System
Recall that the suffix -oma means tumor. The term for a slow-growing benign tumor arising from bone is osteoma, and a tumor arising from cartilage is called a chondroma.
Sarcomas are malignant tumors that arise from connective tissue, such as bone, muscle, and other tissues that make up the musculoskeletal system. Thus, a sarcoma that arises from cartilage is called a chondrosarcoma. An osteosarcoma is a specific type of sarcoma arising from bone. The illustration shows an osteosarcoma at the lower end of the femur. Myosarcoma is the term for a malignant tumor arising from muscle. Recall that the combining form that refers specifically to striated muscle is rhabdomy/o; therefore, a sarcoma arising from striated muscle tissue is called a rhabdomyosarcoma.
Multiple myeloma is another type of malignant disease of bone. You will recall that myel/o means marrow and also refers to the spinal cord. In this case, it refers to marrow because multiple myeloma arises from plasma cells in bone marrow.
You will recall from Module 7 that leukemia is a general term that refers to a variety of malignant bone marrow diseases involving white blood cell formation. All of the leukemias involve replacement of normal bone marrow with proliferating leukocytes and their stem cells. Although leukemia arises from bone marrow, it is generally considered to be a disease of the blood rather than of the bone.
A myofibroma is a benign neoplasm composed of myofibroblasts (embryonic muscle fiber cells) in the connective tissues. It usually occurs in multiple locations at once and is often congenital. This condition is also referred to as myofibromatosis.
2.1 Threaded Case Study: Mrs. Nouri
Before we study the various kinds of tests used to diagnose musculoskeletal problems, let's return to our case study patient.
Mrs. Nouri's pain has spread to her heel, still seeming to her to originate in the small of her back. Her physician suspects that her herniated disk may be involving pressure on more than one nerve root.
2.2 MRI and CT Scanners
In many cases of pain related to the musculoskeletal system, x-rays or radiographs are a good choice for initial diagnostic testing because they can help identify any structural damage or defects related to trauma or congenital abnormalities.
After that, a logical next step in diagnosis may be magnetic resonance imaging (MRI) or a computed tomography (CT) scan. These tests provide additional information that supplements that gained from the conventional x-ray examination.
2.3 Threaded Case Study: CT Scan of Herniated Disk
Mrs. Nouri does indeed have a herniated disk. In this CT scan, can you locate the herniated disk?
The large light rounded area in the center of the image is the vertebral body. The Y-shaped bone below it represents the laminae and the spinous process. Within the hollow between the body and the laminae is a light-colored oval, slightly to the left of the center. That is the spinal cord. The disk herniation, the ruptured nucleus pulposus, is the medium gray area just to the right of the spinal cord. You can see that it is crowding the neural foramen and forcing the spinal cord to the side.
2.4 Threaded Case Study: MRI Scan of Herniated Disk
Here we see an MRI of Mrs. Nouri's lumbar spine. The CT scan showed an axial, or cross-sectional, view of the spine. In this image, we see a side view, or sagittal section.
Again you can see the herniated disk. Its location is posterior to the L4-L5 disk space and is indicated by the arrows.
2.5 Electromyography and Diskography
If the surgeon wants to determine the severity of nerve irritation or to rule out the possibility of peripheral neuropathy, the electromyogram (EMG) might be the diagnostic procedure of choice. Electromyography involves measuring and recording the strength of muscle contraction as a result of electrical stimulation.
You should recognize the word parts that make up the term electromyography. Electr/o denotes a relationship to electricity, my/o means muscle, and -graphy is the process of recording.
Another method of evaluating intervertebral disks is to perform a diskogram. As seen in the illustration on the right, this radiographic procedure involves injection of a contrast medium into the center of the disk, the nucleus pulposus.
2.6 Arthrography
Arthrography is a term that literally means the process of making a record or image of a joint. The term is derived from arthr/o, meaning joint, and -graphy, the process of recording. In practice, the term arthrography refers specifically to the procedure of examining a joint radiographically after the injection with opaque contrast material into the joint capsule.
A number of different joints may be examined by means of arthrography. Among the most common are the knee, the shoulder, and the ankle.
Here you can see an example of the resulting image, which is called an arthrogram.
2.7 Bone Scan
Bone scan images, like those shown here, are obtained by injecting a radioactive substance intravenously and mapping the substance's uptake with a special scanning device called a gamma camera.
Excessive uptake indicates increased metabolism in the area and can help pinpoint the location of pathology that is associated with increased metabolic activity, such as tumors, infection, inflammation, or stress fracture.
Decreased uptake is an indication of decreased or absent metabolism in the area and may be an indication of necrosis (tissue death) or ischemia (lack of blood supply).
2.8 Bone Densitometry
Bone density measurement is called densitometry. These tests aid in the diagnosis of osteoporosis, a disease characterized by loss of bone mass and increased porosity within the bone. Osteoporosis is a term that combines oste/o, meaning bone, and -porosis, a suffix that means condition of pores or spaces. Osteoporosis frequently leads to fractures after only minimal trauma.
When osteoporosis is suspected, physicians may recommend a specific bone density test called a DEXA scan. DEXA stands for dual-energy x-ray absorptiometry. This procedure involves taking x-rays of bones in the lumbar spine.
Other types of densitometry involve CT scans and peripheral detection methods that measure bone density of the spinal column, pelvis, heel, or wrist. All bone densitometry methods involve an x-ray detector that measures x-ray penetration of the bone.
2.10 Arthrocentesis (video)
In addition to imaging studies and laboratory tests, certain other clinical procedures are valuable in diagnosing, as well as treating, musculoskeletal disorders.
A muscle biopsy, surgical removal of tissue for microscopic examination, may be the best diagnostic alternative when neoplasms or certain infectious processes are suspected.
In arthrocentesis, as seen in the video, the joint space is punctured with a surgical needle and synovial fluid is removed. The term arthrocentesis is formed from arthr/o, meaning joint, and -centesis, surgical puncture to remove fluid.
Arthrocentesis may be performed to remove excess fluid from the joint capsule that accumulates due to inflammation, often as a result of trauma. In such a case, arthrocentesis serves to alleviate pain and relieve stress on the tissues of the joint.
Arthrocentesis may also be used as a diagnostic tool to remove synovial fluid for laboratory analysis.
2.11 Arthroscopy
You will recall that the suffix -scopy means visual examination and -scope refers to an instrument that aids visualization, often a fiber-optic instrument. Thus, arthroscopy is the visual examination of a joint such as the knee, ankle, or shoulder using a specific type of endoscope called an arthroscope.
The arthroscope incorporates small surgical instruments for making surgical repairs within the joint.
2.12 Orthopedics
Orthopedics is the branch of health care concerned with preserving and restoring the function of the skeletal system. An orthopedic surgeon performs surgical operations to treat conditions of the musculoskeletal system. The term orthopedics is derived from orth/o, meaning straight. Now let's consider some of the terms common to orthopedics.
You will recall that plastic surgery to make structural repairs is indicated by the suffix -plasty. Thus, repair of a bone is called osteoplasty, and the repair of a joint is termed arthroplasty. Similarly, plastic surgery to repair a vertebra is called vertebroplasty. Surgical repair of cartilage is chondroplasty.
The process of cutting into a bone is called an osteotomy; the instrument used to perform an osteotomy is called an osteotome. The illustration demonstrates an osteotomy of the tibia for a valgus deformity ("knock knee").
2.13 Fracture Treatment
One aspect of orthopedic practice is the treatment of musculoskeletal trauma that involves dislocations or fractures. Simple, undisplaced fractures may require only immobilization; that is, the application of a cast or splint.
The realignment of dislocated bones or displaced fracture fragments is called reduction. This is often accomplished by applying traction, a pulling stress on the distal bone or fragment that allows it to be repositioned. This type of reduction is called a closed reduction.
An open reduction is a surgical procedure in which the skin is incised to permit access to the bone or bones. Open reduction usually also involves internal fixation, the process of securing the bone fragments in place using surgical hardware such as screws, nails, and sometimes plates. Hip fractures are usually treated by means of open reduction and internal fixation, but this type of procedure may be needed for many other types of fractures as well.
In cases where the stress of strong muscles tends to pull fracture fragments out of alignment, a temporary form of traction is accomplished by means of external fixation. External fixation (top right figure) involves the insertion of pins through the bone that are attached to a steel rod outside the limb. External fixation is used primarily to stabilize transverse fractures.
2.14 Ostectomy
The term for excision of a bone is ostectomy, also spelled osteectomy. Sometimes the procedure is named for the specific bone that is removed; for example, a coccygectomy is the excision of the tailbone and a phalangectomy is the surgical removal of a phalanx.
Correction of problems involving cartilage may require surgical removal of the cartilage, which is called chondrectomy. The term meniscectomy refers specifically to the surgical or arthroscopic removal of all or part of the meniscus cartilage of the knee.
Costectomy refers to the surgical removal of a rib, as seen in this illustration.
Sternotomy combines stern/o (sternum) and -otomy (to cut into) to form this term that means to cut through the sternum. A sternotomy is necessary to provide access to the heart for open-heart surgery.
2.15 Total Hip Arthroplasty
An example of orthopedic surgery is illustrated here. This patient has received a total hip replacement, also called total hip arthroplasty. You will recall that the suffix -plasty means surgical repair; thus, arthroplasty is surgical repair of a joint. In total hip arthroplasty, the femoral head and acetabulum are replaced with prostheses that are cemented into the bone. This procedure can make a dynamic improvement in the quality of daily life for the individual with advanced arthritis of the hip.
2.16 Arthroclasis and Arthrodesis
When ankylosis causes a joint to be so stiff that it cannot move, the surgical treatment to permit movement of the joint is called arthroclasis. The suffix -clasis means to break. Osteoclasis is the term for intentional surgical fracture or refracture of a bone to correct a deformity.
When damage to cartilage or ligaments causes a joint to be unstable or causes severe pain with motion, the appropriate treatment may be arthrodesis, the surgical fusion of the joint. The suffix -desis means fusion. The illustration demonstrates an anterior cervical fusion where the intervertebral spaces have been filled with bone chips.
2.17 Other Musculoskeletal Surgeries
There are many types of surgical procedures to correct problems with the soft tissues of the musculoskeletal system. For example, tenotomy is the term for cutting into or dividing a tendon. Suturing of a tendon, on the other hand, is tenorrhaphy. Suturing of a muscle is called myorrhaphy.
In cases of trauma, repetitive stress, infection, or crystal deposits such as those that occur with gout, it is sometimes necessary to remove a bursa to promote healing of the joint. The term for excision of a bursa is bursectomy.
2.18 Threaded Case Study: Mrs. Nouri
Because Mrs. Nouri is quite physically fit, it was hoped that traditional treatment with physical therapy, pain medication, and bed rest when necessary would relieve her symptoms. However, her disk has protruded farther and both her low-back pain and her sciatica have worsened to the extent that it is hard for her to function. Her physician asserts that it is time for surgical intervention.
2.19 Threaded Case Study: Laminectomy
With chronic or recurrent disk herniation, laminectomy, seen here, may become necessary.
A laminectomy is so named because it requires surgical resection (excision) of a portion of the vertebral arch, the lamina. This allows access to the protruding disk so that all or part of it can be removed.
In Mrs. Nouri's case, however, the orthopedic surgeon opts to remove the disk by aspirating it through a tube inserted through the skin. This procedure is much less invasive; it is called endoscopic diskectomy. This term may also be spelled discectomy; it means excision of a disk.
Introduction
In this module, you will learn more about the medical terms associated with the nervous system and the special sensory organs. When you complete this module, you should be familiar with terms that describe the structure and functions of this system. You should have a good understanding of terms that specify physical disorders affecting the nervous system as well as psychological disorders. You should be able to recognize terms for tests and procedures that are used to diagnose and treat nervous system diseases and disorders. As you work through this module, you may need to refer to the basics of word structure that were introduced in Module 1.
This integrated learning program is intended as a supplement to your text—not as a substitute. Be sure to keep your text available for ready reference.
Objectives
In this module, you will learn to:
- Match the major divisions of the nervous system with their functions.
- Match the structures of the nervous system with their descriptions.
- Identify the stimulus for each of the five types of receptors.
- Use the word parts to build and analyze terms.
- Match several disorders of the nervous system with their characteristics.
- Use word parts to determine the meanings of terms.
- Write the meanings of the abbreviations.
In this module, you will learn to:
- Match the major divisions of the nervous system with their functions.
- Match the structures of the nervous system with their descriptions.
- Identify the stimulus for each of the five types of receptors.
- Use the word parts to build and analyze terms.
- Match several disorders of the nervous system with their characteristics.
- Use word parts to determine the meanings of terms.
- Write the meanings of the abbreviations.
Right now, as you sit before the computer, you are engaged in a variety of activities. You're seeing and reading the information on the screen. Simultaneously, you may be listening to the narration and using the mouse or the keys to interact with the program. You're also processing the information, storing it in your memory, recalling what you've learned previously, screening out distractions, breathing, maintaining a regular heartbeat, and monitoring and responding to a host of changes in your internal and external environments.
Obviously, you're performing some of these tasks voluntarily; others are not within your awareness. But don't worry! Your nervous system is on the job, carefully coordinating each and every thing you do.
1.2 Threaded Case Study: David Goldman
As we begin to explore how the nervous system works, let's meet David Goldman, who seems to be experiencing some neurologically based health problems. David, 57, teaches English at the local university. During the past year, he's grown increasingly concerned that difficulties with attention and concentration are interfering with his performance in the classroom.
David explains to his doctor, Dr. James, that he tends to get confused or lose track of his thoughts during a lecture. Dr. James has decided to refer him to the university medical center's neurology service to help assess these complaints. We'll return shortly to accompany David as he visits the neurologist.
You'll notice that, throughout our discussion of the nervous system, we'll encounter the combining forms neur/o and nerv/o, meaning nerve, in a variety of terms. For example, nervous and neural both mean pertaining to nerves.
1.3 Function of the Nervous System
If the circulatory system can be described as the body's transportation system, the nervous system might be thought of as its communications infrastructure—a high-speed information network. Together with the glandular secretions of the endocrine system, the nervous system keeps the body functioning as an integrated whole.
The activities of the nervous system may be classified according to whether they are sensory, motor, or integrative in nature. Sensory functions detect sensation; motor functions initiate movements; and integrative functions produce thoughts, store memory, and make decisions.
1.4 Physical Divisions of the Nervous System
The nervous system is one of the most complex body systems. Let's begin our review of its structure and function by considering its two main divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).
The central nervous system consists of the brain and spinal cord. This division is called the central nervous system because of the central or midline position of the brain and spinal cord in the body.
The peripheral nervous system is composed of bundles of impulse-carrying nerve cell fibers: 12 pairs of cranial nerves and 31 pairs of spinal nerves that transmit information to and from the central nervous system. This division of the nervous system is called peripheral because the nerves extend to the outlying or peripheral parts of the body.
1.5 Cranial and Spinal Nerves
The cranial nerves originate at the base of the brain and carry signals to and from the structures of the head and neck and the thoracic and abdominal cavities.
Spinal nerves, which are attached to the spinal cord, communicate with the chest, abdomen, and extremities, making sensation and movement possible.
1.6 Peripheral Nervous System
The peripheral nervous system consists of two components: one regulates voluntary functions and the other controls involuntary functions.
Voluntary or conscious activities, such as walking, chewing, or swinging a bat, are controlled by the component known as the somatic nervous system. The term somatic means pertaining to the body; the combining form somat/o denotes a relationship to the body. Of course, the entire nervous system is part of the body, but in this case, somatic refers to our body awareness.
Involuntary functions, such as the heartbeat and stomach contractions that usually occur without our conscious awareness, are regulated by the autonomic nervous system (ANS). You will recall that the prefix auto- means self. The term autonomic is similar in meaning to automatic and refers to the ability to function independently without outside influence.
1.7 Autonomic Nervous System
The autonomic nervous system is organized into two main divisions: the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system prepares the body to act during times of stress—that is, to undergo the complex changes known as the fight-or-flight response.
The parasympathetic nervous system tends to have opposite effects to the sympathetic system. It is most active in the body's restorative processes, such as digestion; it is dominant when the individual is nonthreatened and relaxed. Parasympathetic system activities tend to result in energy being conserved and stored.
1.8 Sympathetic Nervous System
Strenuous exercise and strong emotions, such as fear and anger, sound alarms within the body to which the sympathetic nervous system responds. The illustration shows how this system reacts by increasing the heart rate, supplying the muscles with more blood, slowing digestion, and increasing glandular secretions. These changes prepare the body for the muscle work an emergency may require.
1.9 Parasympathetic Nervous System
The nerves of the parasympathetic nervous system send signals that act to protect, conserve, and restore the body's resources. They frequently act to counter the effects of the sympathetic nervous system.
For example, after a person has reacted to an emergency, the parasympathetic nervous system will respond by slowing the heart rate, lowering the blood pressure, increasing the secretion of digestive juices, and relaxing muscles of the digestive system that control elimination.
1.11 Neuron Structure (animation)
The structures of the nervous system are formed from two types of cells—neurons, or nerve cells, and connective tissue cells, called neuroglia, that serve as support cells for the neurons. Neuroglia are also called glial cells, or simply glia. The combining form gli/o denotes a relationship to neuroglia or to a sticky substance.
Neurons perform the essential work of the nervous system, communicating information to and from other body structures.
Each neuron consists of a cell body; a number of branching projections called dendrites; and one long threadlike extension, the axon. The combining form dendr/o in the term dendrite is defined as tree and refers to the branchlike processes that extend from the neuron's cell body.
1.12 Axon Structure
Some axons are surrounded by a white-segmented wrapping called a myelin sheath. Myelin is a fatty substance formed by special cells that perform supporting and connecting functions. Between the myelinated segments of the axon are gaps in the myelin sheath known as the nodes of Ranvier.
Since myelin appears white, tissue composed of myelinated axons is called white matter. Nerve tissue that is not myelinated appears gray and is called gray matter.
As this lesson progresses, you'll learn how messages, in the form of nerve impulses, are sent to and from the brain. These impulses travel much more quickly along myelinated nerve fibers.
1.13 Neuron Impulses (slide show)
Neurons are excitable, that is, they are capable of being stimulated by electrical impulses and of transmitting those impulses along their cell length.
Functionally, neurons are categorized according to the direction in which they transmit signals. Afferent, or sensory, neurons send impulses to the brain and spinal cord from special receptors in all parts of the body. Efferent, or motor, neurons conduct impulses away from the brain and spinal cord toward the muscles and glands.
1.14 Impulse Conduction (animation)
So how do neurons, the "wires" of our body's communication system, work? Impulse conduction begins when the receptors of our sensory neurons detect a change in the environment. Sensing a stimulus, such as a tap on the shoulder or an increase in temperature, sets off complex chemical changes in the neuron. These chemical changes, in turn, create an electrical disturbance—an impulse—that moves like a wave along the length of the cell, from the dendrite to the axon.
1.15 Synapse
Most impulses must pass through several neurons to reach their destinations. To pass from one nerve cell to the next, the impulse must cross a microscopic space between neurons called the synapse.
When the impulse reaches the terminal end fibers of the axon, it causes the release of special chemicals called neurotransmitters. These chemicals bind to proteins on the membrane of the adjacent neuron, inducing an electrical impulse in that nerve cell. Acetylcholine, epinephrine, dopamine, and serotonin are examples of chemicals that have been identified as neurotransmitters.
|
|
|
2.1 Meninges
The brain is one of the largest and most complex organs in the body. It consists of about 100 billion neurons and 900 billion neuroglia.
For its protection, the brain is encased within the skull, or cranium. The combining that means cranium is crani/o.
In addition, the brain is enclosed in three layers of protective membranes, collectively known as meninges. The combining form that means meninges is mening/o, and meningeal means pertaining to the meninges.
Individually, the meningeal layers are the dura mater, the thick outermost layer; the arachnoid membrane, a loosely attached weblike covering; and the pia mater, the delicate, inner layer with a rich supply of blood vessels that nourishes the nervous tissue.
The name of the arachnoid membrane is derived from arachn/o, which also means spider, and the suffix -oid, which means like or resembling; thus, arachnoid means spiderlike, and the name of the membrane is drawn from its resemblance to a spider web.
2.2 Divisions of the Brain
There are four major divisions of the brain: the cerebrum, the cerebellum, the diencephalon, and the brainstem.
The combining forms encephal/o and cerebr/o are used to refer to the brain. The term cerebral means pertaining to the brain. As you will see in the next frame, cerebr/o can also refer specifically to the cerebrum, one division of the brain.
2.3 Cerebrum
The cerebrum is the largest and uppermost section of the brain. As you can see, the term cerebrum incorporates the combining form cerebr/o.
The surface of the cerebrum, the cerebral cortex, has many folds, called convolutions or gyri (sing., gyrus), and grooves, called sulci (sing., sulcus). Very deep grooves are called fissures; the deepest groove is called the interhemispheric fissure. It divides the cerebrum into right and left halves, called hemispheres. The term hemisphere is from hemi-, meaning half, and spher/o, meaning globe-shaped. You will recall that the prefix inter- means between; thus, interhemispheric means between the hemispheres.
The cerebral hemispheres are connected by a band of millions of nerve fibers deep in the brain called the corpus callosum. These fibers are the axons of cells in the cerebral cortex.
2.5 Frontal Lobe
Each cerebral hemisphere is divided into four lobes, named for the overlying cranial bones.
The frontal lobe is the largest of the lobes. It is responsible for voluntary control over most of the skeletal muscles. The frontal lobe also influences personality and is associated with higher mental processes, such as reasoning, judgment, planning, and conceptualization.
2.6 Temporal Lobe
The temporal lobe is found in the lateral region of the cerebrum. This lobe is involved with the functions of hearing, taste, smell, and balance; association areas for memory and learning are also located within the temporal lobe.
2.7 Parietal Lobe
The parietal lobe lies behind the frontal lobe and above the temporal lobe. Areas of the parietal lobe serve as centers for language and general sensory functions.
2.8 Occipital Lobe
The occipital lobe occupies a relatively small, pyramid-shaped area in the posterior part of the cerebrum. It is within this lobe that visual images are registered; the occipital lobe also contains the visual associative areas, which enable interpretation of images.
2.11 Cerebellum
The cerebellum, the second largest part of the brain, lies under the posterior portion of the cerebrum. It is indicated in medical terms by the combining form cerebell/o.
The cerebellum is responsible for our ability to perform coordinated and smoothly executed movements. Through its many afferent and efferent connections to other areas of the central nervous system, the cerebellum also helps us to maintain our balance and posture.
2.12 Thalamus and Hypothalamus
The diencephalon, which lies under the cerebrum, is a small portion of the brain, but it contains two very important structures: the thalamus and the hypothalamus.
The thalamus serves as a major sensory relay station, directing impulses to the cerebral cortex. The thalamus also helps to associate sensation with emotions so that we recognize a sensory experience as pleasant or painful.
The hypothalamus, as its name implies, lies inferior to the thalamus. The hypothalamus exerts control over virtually all of the internal organs. It activates and integrates functions of the autonomic nervous system and processes of the endocrine system. The hypothalamus helps to maintain the body's water balance, helps to regulate the body temperature and sleep cycles, and is involved in the control of appetite and in the experience and expression of many emotions.
2.13 Brainstem
The fourth major division of the brain is known as the brainstem. The brainstem actually comprises three structures: the medulla oblongata, the pons, and the midbrain.
2.14 Brainstem Structures
The medulla oblongata, the lowest part of the brainstem, is an upward extension of the spinal cord.
The pons, a term that literally means bridge, lies between the medulla and the midbrain.
The midbrain is involved in functions such as vision, hearing, eye movement, and body movement. The anterior part has the cerebral peduncle—which is a huge bundle of axons traveling from the cerebral cortex through the brainstem—and these fibers are important for voluntary motor function.
The brainstem structures serve as two-way conduction paths and contain many important reflex centers. These centers help to control respiration, heart rate, and blood vessel diameter.
2.15 Ventricles
Within the brain are several fluid-filled cavities called ventricles. The fluid that circulates within the ventricles, as well as around the brain and spinal cord, is known as cerebrospinal fluid (CSF).
Together with the protective skeletal and membranous coverings of the brain, cerebrospinal fluid helps to cushion and protect the vital nervous system structures.
2.17 Threaded Case Study: David Goldman
Before we continue with this lesson, let's join David at the neurologist's office. David's wife, Fran, is also present to share her observations of David at home. The neurologist conducts a thorough history and learns that David is in good physical health and has attempted to stay fit and active by riding his bike to campus each day. As part of his family's medical history, David reports that his father experienced an early onset of problems with memory and a loss of intellectual ability.
Fran says she notices at home that David displays a loss of initiative, has some difficulty with decision-making, and is less interested in socializing with friends.
The neurologist records these findings in an attempt to develop a complete understanding of David's problems. He decides to perform and authorize additional diagnostic testing. We'll rejoin David shortly as he undergoes the recommended procedures.
2.18 Spinal Cord
The spinal cord is a long, cylindrical structure that extends from the medulla oblongata to the upper part of the lumbar region, just above the pelvis. In the average adult, the spinal cord measures about 18 inches in length.
Perhaps you recall from the previous module that the combining form that means spinal cord is myel/o. This same word part is used to refer to the bone marrow.
2.19 Spinal Canal
The spinal cord is contained within the vertebral canal, which runs through the protective spinal column. Similar to the brain, the spinal cord has three layers of meningeal covering.
In addition to the spinal cord and its covering membranes, the vertebral canal contains the cerebrospinal fluid, a cushion of fatty tissue, and blood vessels.
The 31 spinal nerves are attached to the spinal cord and are named for the level of the vertebral column from which they emerge. Thus, the spinal canal is said to have cervical, thoracic, lumbar, sacral, and coccygeal segments. You'll recall these terms from Module 14, which described the muscular and skeletal systems.
2.20 Spinal Cord Functions
The spinal cord performs two major functions. First, it conducts impulses to and from the brain. Sensory impulses travel to the brain along ascending nerve tracts, and motor impulses are conducted from the brain on descending tracts.
Second, the spinal cord functions as the body's primary reflex center, a switching station that initiates the function or movement of an organ or body part in response to a stimulus.
2.21 Reflex Arc (animation)
A reflex arc is a simple nerve conduction pathway by which the body responds directly to stimuli without mediation by the brain.
Let's look at a simple example of how reflex impulse conduction works. In the animation, the stimulus is the rubber hammer used during physical assessment of the knee-jerk response. Sensory receptors in the muscles and tendons detect the hammer's tap and generate a nerve impulse. The impulse travels along the neuron's dendrites, to the cell body, and then along the length of the axon to the spinal cord. There it is relayed to the dendrites of a motor neuron and along the motor neuron's axon to the muscle, which carries out the knee-jerk response.
2.22 Neuromuscular Junction
The neuromuscular junction is the area of contact between a motor neuron and a skeletal muscle. The term neuromuscular means pertaining to nerves and muscles or to the relationship between them.
The motor nerve impulse causes the release of the chemical acetylcholine at the neuromuscular junction. In turn, acetylcholine causes contraction of the muscle. As soon as the muscle contracts, the acetylcholine is neutralized by the enzyme acetylcholinesterase.
3.1 Special Senses
In the previous lesson, we learned about afferent sensory neurons that respond to stimuli in our external environment. Some of these sensory receptors, known as the general sense organs, are widely distributed throughout the body. They enable us to detect pain, pressure, and changes in temperature.
The special senses—smell, vision, hearing, taste, and equilibrium—are characterized by closely grouped receptors that are located in complex organs. In this lesson, we'll look at two of those special sensory organs: the eye and the ear.
3.2 The Eye
The eye is one of a pair of special sense organs that converts the energy of light into electrical nerve impulses and transmits these signals to the brain. In the brain, they are interpreted as sight and recognized as the representation of familiar objects.
It is through the eyes that we gain much of our information about our external environment. The structures of the eye don't merely receive a light stimulus; they adjust the incoming light and adapt to it to form the clearest image. The combining forms ophthalm/o and ocul/o refer to the eye.
3.3 External Structure of the Eye
The eyes are surrounded and supported by a number of specialized structures. They are contained in two bony orbits at the front of the skull. About five-sixths of each eyeball lies within, and is protected by, these bony sockets. Other external structures of the eye include the eyelids, eyebrows, and eyelashes. You will recall that the combining form that means eyelid is blephar/o.
The mucous membrane that lines the inner surfaces of the eyelids and the anterior part of the eye is called the conjunctiva. Each eye has a lacrimal gland that produces tears to moisten and lubricate the eye. The six muscles of each eye are called the ocular muscles.
3.4 Sclera, Cornea
The many structures that make up the eyeball itself are considered to be the internal structures of the eye.
Three fibrous layers cover the eyeball. The sclera is the tough outer membrane that helps to maintain the size and shape of the eyeball and attaches to the muscles that move the eye. The sclera is what we recognize as the white of the eye. The term sclera is related to the combining form scler/o, which means hard, and which also denotes a relationship to the sclera.
The anterior portion of the sclera is the cornea—a convex, transparent structure through which light passes to other parts of the eye. The cornea is indicated in medical terms by the combining form kerat/o that you'll recall also means hard.
3.5 Eye Structures
The eye's middle layer, the choroid layer, is a thin membrane with a rich supply of blood vessels. Anteriorly, the choroid is joined, by means of the ciliary body, to the iris. The iris is the contractile disc that forms the colored portion of the eye.
The pupil is the circular opening in the middle of the iris. Muscles of the iris constrict and dilate the pupil in response to the intensity of light.
The lens is a highly elastic, transparent structure behind the iris that, by changing its shape, helps to focus rays of light.
3.6 Retina
The retina is the innermost layer of the eyeball. It is a thin, delicate membrane that is continuous with the optic nerve through which light impulses are transmitted to the brain. The retina itself is a multilayered structure; the outermost layer contains light-sensitive cells called rods and cones
3.7 Interior Cavities of the Eye
The interior space of the eyeball is divided into two cavities. The anterior cavity consists of anterior and posterior chambers. The chambers of the anterior cavity contain a clear, watery fluid, called aqueous humor, which helps to maintain the shape of the eyeball and to nourish the iris, lens, and cornea.
The posterior cavity of the eyeball occupies all of the internal space behind the lens. It contains vitreous humor, a gelatinlike substance that also helps to preserve the eyeball's shape. The inner, posterior surface of the eye is known as the fundus.
3.9 The Ear
The ear provides the dual function of sensing sound and serving as the organ of balance, or equilibrium. The combining forms ot/o and auricul/o in medical terms indicate a reference to the ear; the word part audi/o refers to hearing.
The ear is divided into three anatomical regions: the external ear, the middle ear, and the inner ear.
3.10 External Ear Structures
The outer ear consists of the auricle, or pinna, and the external auditory meatus, or auditory canal.
The auricle, a skin-covered cartilaginous flap, projects from the side of the head. The external auditory meatus is a slender canal about an inch in length that is lined with glands that secrete a sticky substance called cerumen. Cerumen, called earwax in lay terms, lubricates the ear and prevents the entry of foreign particles into the internal portions of the ear.
3.11 Middle Ear Structures
The tympanic membrane, or eardrum, is a shiny, oval, semitransparent membrane that lies at the inner end of the external auditory canal and at the entry to the middle ear.
Within the middle ear cavity are three small bones, or ossicles—the malleus, incus, and stapes, so named because they resemble a hammer, an anvil, and a stirrup. The auditory ossicles transmit sound vibrations from the tympanic membrane to the inner ear.
The auditory, or eustachian, tube is another structure of the ear that joins the nasopharynx with the middle ear cavity. The eustachian tube provides equalization of air pressure between the middle ear and the external atmosphere.
3.12 Inner Ear Structures
The inner ear is composed of a membranous labyrinth inside of a bony labyrinth. The bony labyrinth consists of three parts: the vestibule, the cochlea, and the semicircular canals.
The cochlea houses a sensitive receptor whose hair cells relay sound waves to auditory nerve fibers. These fibers then convey impulses to the auditory region of the cerebral cortex. Structures within the vestibule and semicircular canals help us maintain balance and equilibrium.
|
|
|
3.13 Threaded Case Study: David Goldman
David's neurologist continues his assessment of David's nervous system, examining his eye and facial movements as well as his muscle strength and reflexes. To rule out visual and auditory perceptual problems, the neurologist has examined David's eyes and ears.
1.1 Diseases of the Nervous System (slide show)
Diseases of the nervous system can be categorized in a variety of ways. We can consider the causes of a disease—whether, for example, its source is an infection or an inherited trait. We can analyze the duration of the illness. Is it acute or chronic? Does it worsen over time? We can also look at the anatomic structures or functions affected by the condition. Does it affect the brain? The spinal cord? Both of those structures? The peripheral nervous system?
In this section, we'll look at a range of pathologic conditions that affect the nervous system, including congenital, infectious, neoplastic, traumatic, vascular, degenerative, movement, and seizure disorders. We'll also review disorders of the special sense organs and consider some major categories of psychologic disorder.
1.2 Headache
Before beginning to look at specific disorders, let's look at the phenomenon of cephalic pain, more commonly known as headache. Headache is abbreviated HA and is also referred to as cephalalgia or cephalgia. A headache may be a symptom of numerous disorders and from a variety of causes.
The headache pain may be diffuse or focal, acute or chronic, mild or almost unbearably intense. Causes of headache include infection, metabolic disorders, trauma, nervous tension, and exposure to toxic substances. Treatment for headache is usually pharmacologic and depends on the cause of the pain.
1.3 Congenital Conditions
Now let's consider two congenital conditions, disorders with symptoms that are present from birth. The first involves the incomplete closure, during prenatal development, of the skull or the vertebral column. A meningocele is the name given to the saclike protrusion that forms when the meninges covering the brain or spinal cord push through a defective bony enclosure of the central nervous system. If both the meninges and the spinal cord protrude, a meningomyelocele is created. Neurologic deficits can accompany this condition, depending on the amount of nerve tissue involved. Surgery is often necessary to remove the herniated tissue.
1.4 Circulatory Pathway of Cerebrospinal Fluid
You'll remember that in looking at the anatomy of the nervous system, we learned about the presence of cerebrospinal fluid (CSF), which provides a protective cushion for the brain and spinal cord. Interference with the fluid's circulation, or an imbalance in the production and absorption of CSF, can result in its accumulation, usually under pressure, within the ventricles of the brain.
1.5 Hydrocephalus
This condition of fluid accumulation within the cerebral ventricles is known as hydrocephalus—literally, water in the head. Hydrocephalus may be congenital or may have a later onset. Causes of the condition include developmental abnormalities—such as myelomeningocele, which we saw previously—infection, injury, and brain tumors.
1.6 Treatment of Hydrocephalus
Infants with hydrocephalus have an enlarged head, a disproportionately small face, and eyes that appear depressed within the sockets. Treatment consists of surgical intervention to relieve pressure on the brain by inserting a tube, called a shunt, to drain the excessive cerebrospinal fluid.
1.7 Inflammatory Conditions of the Nervous System
Now let's consider some infectious and inflammatory conditions of the nervous system. As we've seen in previous modules, we can rely on our old friend, the suffix -itis, in combination with word parts identifying specific anatomy, to form many disease and disorder terms that involve inflammation. In this way, we can build the terms duritis, inflammation of the dura mater; cerebellitis, inflammation of the cerebellum; and encephalitis, inflammation of the brain, shown in the accompanying illustration.
Based on what you've learned about word parts, what does the term polyneuritis mean?
1.8 More Infectious Diseases of the Nervous System
If you guessed that polyneuritis means inflammation of many nerves, you're right!
As you can imagine, the types of infectious disease affecting the nervous system are far too numerous to describe in detail here. A few others you may have heard about are poliomyelitis, in which viral infection leads to inflammation of spinal cord tissue and muscle paralysis; tetanus, in which bacterial infection causes muscle stiffness and sustained spasm; and botulism, where the ingestion of food containing bacteria-produced toxins can progress to central nervous system paralysis.
1.9 Meningitis
Let's learn a little more about a representative disorder within this category.
Meningitis is an inflammatory condition that affects the brain and spinal cord. Infecting agents such as bacteria, viruses, or fungi enter the central nervous system through the bloodstream or as a consequence of an upper respiratory infection. The microorganisms cause acute inflammation of the pia mater and arachnoid membranes. Depending on its specific cause, meningitis may range from a mild form of the disorder to one that is potentially fatal.
Symptoms of meningitis include severe headache, fever, and neck stiffness. Deafness, blindness, paralysis, and mental retardation are among the possible residual effects.
1.10 Sciatica (animation)
Sciatica is an inflammatory condition involving the long nerve that extends through the muscles of the thigh, leg, and foot. This disorder is usually marked by pain and tenderness along the nerve's course. Sciatica may be caused by trauma to, or compression of, the nerve or its roots and may result in muscle wasting of the lower leg.
1.11 Lumbar Puncture
Before we move on to consider neoplastic disorders of the nervous system, let's look at a diagnostic method, cerebrospinal fluid analysis, which is used to provide information about many conditions of the central nervous system, including some of those we're reviewing. Cerebrospinal fluid is withdrawn by inserting a needle into the spinal cavity during a procedure known as a lumbar puncture (LP) or spinal tap. After the fluid is aspirated, it is sent to the laboratory for examination, where the presence of infection and other central nervous system abnormalities can be detected.
1.12 Neuromas
Tumors of the nervous system may be benign or malignant. A neuroma is a tumor composed of nerve cells, as we can tell by defining the word parts. It is a benign neoplasm. An example of this type of growth is the acoustic neuroma, a tumor that develops on a cranial nerve and grows within the auditory canal. It's important to remember that even a benign tumor can prove life-threatening when it arises within the brain because of the tumor's ability to compress and displace brain tissue within the confines of the skull.
1.13 Gliomas
Tumors of the brain may be either primary—arising from within the brain tissue—or secondary, the result of cancerous cells having metastasized from another site in the body. About 25% to 30% of brain tumors are metastatic growths. Most primary brain tumors form from the meninges, called meningiomas, or from neuroglial cells, which are referred to as gliomas. A wide range of symptoms is associated with brain tumors, depending on the lesion's location and the surrounding structures it displaces.
1.14 Diagnostic Tests to Detect Brain Tumors
Many diagnostic tests are used to detect the presence of a brain tumor. Among them is computed tomography (CT) (Fig. A), which is used to produce an image that provides detailed cross sections of brain tissue. Magnetic resonance imaging (MRI) (Fig. B) uses magnetic waves to create an image of the brain. Because of its sensitivity, MRI is especially useful in the detection of small tumors.
1.15 Surgical Treatment for Brain Tumors
Surgical removal is the treatment of choice for brain tumors. Radiation therapy and chemotherapeutic medications are used to treat tumors that can be only partially removed. Stereotactic radiosurgery (also called stereotaxic radiosurgery), seen in the illustration, involves the use of an instrument that helps to target the precise location of a tumor and then delivers a focused beam of radiation to destroy the tumor.
1.16 Threaded Case Study: David Goldman
Now let's see how the diagnosis of David's complaints is progressing. From our discussion of diagnostic methods used to detect brain tumors, we know that David is undergoing computed tomography and magnetic resonance imaging. These procedures will help detect the cause of the problems he's experiencing.
2.1 Concussion
Head injury describes any traumatic damage to the scalp, skull, and/or brain tissues. The damage may range from a minor wound to penetration of the skull with severe injury to brain structures. An estimated 3 million people suffer head injuries each year in the
Brain injuries may be categorized as minor or major. A concussion, a violent shaking up or jarring of the brain with no apparent damage to brain tissue, is an example of a minor injury. The person who receives a concussion may be slightly dazed after the injury or may experience impaired consciousness, either a state of partial awareness (i.e., semiconsciousness), or brief unconsciousness, a state in which awareness of one's surroundings is lost and there is an inability to respond to sensory stimuli. There may also be an inability to recall the injury-causing event; however, recovery from symptoms of concussion is usually prompt.
2.2 Contusion
A more serious type of head injury, a contusion, involves the bruising of brain tissue caused by movement of the brain inside the skull following blunt trauma. The brain may be injured at the site of its impact against the cranial wall (coup) as well as by rebounding against the opposite skull surface (contrecoup).
2.3 Hematomas
With contusion, swelling of brain tissue—i.e., cerebral edema—and damage to the brain's vasculature can occur, causing bleeding and the accumulation of blood—a hematoma—within the cranium. Specific medical terms are used to inform us of the site of the hematoma. A subdural hematoma is a collection of blood between the dura mater and the arachnoid meningeal layers. With an epidural hematoma, blood accumulates between the dura mater and the inner surface of the skull, whereas an intracerebral hematoma involves amassing of blood within the brain. Severe trauma may also lead to coma, a state of profound unconsciousness. A serious head injury may result in persistent neurologic problems.
In many accidents where there is traumatic injury to the head, a concurrent injury is sustained by the spinal cord. Common spinal cord injuries—fractures and dislocations—occur in response to violent impact and forceful movement, examples of which include rotation, compression, hyperextension, and hyperflexion. Such trauma can result in varying degrees of paralysis—the loss of muscle function and/or sensation—depending on the site of injury.
2.4 Cerebrovascular Accident (Stroke)
Cerebrovascular accident (CVA), also known as stroke, cerebral infarction, or brain attack, is the third leading cause of death in the
2.5 Types of Stroke
Thrombosis, the formation of a clot or the accumulation of hardened fatty deposits within a blood vessel, is the most frequent cause of stroke. The clot or fatty deposits narrow and eventually block, or occlude, the vessel opening, disrupting the flow of blood.
Cerebral hemorrhage involves bleeding within the brain from a ruptured cerebral blood vessel (Fig. A). The vessel may have undergone degenerative changes caused by disease, may have been subject to a penetrating injury, or may have a localized weakness in its wall, called an aneurysm (Fig. B), that dilates and bursts. Another cause of stroke, embolism (Fig. C), involves the movement of a clot from a site outside the brain, through the bloodstream, to the neurovasculature. Most emboli originate in the heart.
2.6 Manifestations of Stroke
The manifestations of stroke depend on the location and size of the area in the brain that has been affected and the rate of onset of the stroke. Paralysis, weakness, sensory change, speech defect, or death may occur. Hemiplegia, monoplegia, diplegia, paraplegia, and quadriplegia indicate areas of the body affected by paralysis.
| |||||||||||
troke or brain attack is a sudden problem affecting the blood vessels of the brain. There are several types of stroke, and each type has different causes. The three main types of stroke are listed below. Click on the individual name of each type for more detailed information and images. 
> click on the image for more information about ischemic stroke" v:shapes="_x0000_i1038" border="0" height="95" hspace="2" width="100">
> click on the image for more information about intracerebral hemorrhage" v:shapes="_x0000_i1041" border="0" height="95" hspace="2" width="100">
> click on the image for more information about subarachnoid hemorrhage" v:shapes="_x0000_i1044" border="0" height="93" hspace="2" width="100">2.8 Diagnosing Stroke
Gradual occlusion of a blood vessel may be signaled by the occurrence of temporary neurologic disturbances known as transient ischemic attacks (TIAs). Clinical procedures used to assess TIAs and to diagnose stroke include cerebral angiography (shown in the illustration), the use of contrast dye to visualize the brain's vascular system, as well as computed tomography, magnetic resonance imaging, and lumbar puncture. Echoencephalography, the use of ultrasound to assess cerebral blood flow, can also be a useful diagnostic tool.
Treatment of stroke may include surgical intervention; administration of medications to inhibit the development of, or destroy, thrombi or emboli; initiation of rehabilitation therapy; and introduction of lifestyle changes for the purpose of health promotion.
3.1 Alzheimer Disease
Now let's return to look at some of the major degenerative diseases of the nervous system, so called because they are marked by a deterioration of a range of normal nervous system functions. Alzheimer disease (AD) is a progressive neurological condition that, like other types of dementia, is characterized by a gradual decline in mental ability. Although the etiology of Alzheimer disease is not understood, possible causes include a disordered immune system, viral infection, and genetic predisposition. The condition, which results in structural changes in the brain, sometimes begins as early as middle age and worsens significantly after the age of 70. Its symptoms include memory failure; disorientation—confusion about time, place, or identity; personality changes; speech disturbances; and the inability to perform purposeful movements. Although there is no effective treatment for Alzheimer disease, medication may provide some symptom relief.
3.2 Amyotrophic Lateral Sclerosis (ALS)
Amyotrophic lateral sclerosis (ALS) is a rare degenerative disorder of the nervous system. Also known as Lou Gehrig disease for the famous baseball player who developed the disorder, ALS is marked by a progressive loss of motor neurons. As the motor neurons become incapable of transmitting impulses, weakness of the skeletal muscles ensues. Eventually, the person with ALS has difficulty speaking, swallowing, and breathing. Neither the cause nor a cure for ALS has been found.
3.3 Huntington's Disease
Huntington's disease is a genetically transmitted degenerative disorder caused by a deficiency in specific neurotransmitters produced in the midbrain. Onset of the illness usually occurs between 35 and 45 years of age and is characterized by excessive, involuntary, dancelike movements. Intellectual deterioration and emotional changes accompany progression of the illness. There is no known treatment or cure for Huntington 's disease.
3.4 Multiple Sclerosis (MS)
Multiple sclerosis (MS) is a progressive disorder in which there is destruction of the myelin sheath—the fatty coating that surrounds neurons in the brain and spinal cord. Although the cause of MS is unknown, it is believed to be associated with infectious, immunologic, and genetic factors. As myelin is destroyed, hardened areas of scar tissue replace it. Impulses being transmitted along the axon are slowed by these sclerotic lesions and, eventually, are blocked.
3.5 Myasthenia Gravis (MG)
Myasthenia gravis (MG) is an abnormal neurological condition in which the motor neurons fail to transmit impulses to the muscles to cause contraction. One possible reason for this failure is insufficient production of the neurotransmitter acetylcholine. MG is also believed to have an autoimmune link involving the production of antibodies that are directed against acetylcholine receptors at the neuromuscular junction.
Onset of the symptoms of myasthenia gravis, muscle weakness and generalized fatigue, is usually gradual. Often the facial muscles supplied by the cranial nerves are affected; as a result, the eyelids may droop and chewing and swallowing may prove difficult. As the disease progresses, the respiratory muscles may become involved as well as the skeletal muscles of the lower limbs. There is no known cure for myasthenia gravis, but improvement often follows administration of drugs that prevent the breakdown of acetylcholine.
3.6 Cerebral Palsy
Now we'll turn to disorders of movement or muscle control. Cerebral palsy is a neurological disorder with symptoms that are present at birth or shortly thereafter. The difficulty with motor function that characterizes cerebral palsy is believed to be caused by developmental abnormalities or injury during the early periods of brain growth. Prematurity and lack of an adequate oxygen supply at birth are among the risk factors for this disorder. Symptoms commonly associated with cerebral palsy include partial paralysis; lack of muscle coordination; inability to make purposeful movements; impairment of speech, vision, and hearing; and varying degrees of mental retardation. Treatment can include surgical correction of deformities, the use of braces, medications such as muscle relaxants, and speech therapy.
3.7 Bell's Palsy
Bell's palsy involves paralysis of the seventh cranial nerve, a nerve concerned with facial movement and the sensation of taste. The paralysis, which is usually unilateral, may be caused by trauma to the nerve, compression of the nerve by a tumor, or infection. Herpes simplex vesicles often accompany the onset of Bell's palsy. Loss of taste and the inability to close an eye or to control salivation are common symptoms. The condition can be permanent, but full, spontaneous recovery is likely. Anti-inflammatory and analgesic medications may be administered until the person with Bell's palsy improves.
3.8 Parkinson's Disease
Known as the "shaking palsy," Parkinson's disease is one of the more common chronic nervous system disorders. The cause of Parkinson's disease is unknown, but the pathologic process involves loss of neurons in the midbrain and inadequate production of the neurochemical dopamine (Fig. A). Dopamine has an inhibitory effect on movement and its depletion results in the symptoms associated with Parkinson's disease, the most well-known of which is tremor. Other signs include a shuffling gait, or style of walking; a masklike facial expression; muscle weakness and rigidity; slow movement; and a stooped posture (Fig. B). Treatment of this disorder seeks to provide symptom relief.
3.9 Epilepsy
Epilepsy is a group of disorders, all of which involve an abnormal discharge of electrical activity from the nerve cells of the cerebrum. These sudden uncontrolled bursts of activity from the neurons, also known as seizures, can cause sensory disturbances, involuntary muscle contractions, and loss of consciousness. Some individuals experience an unusual sensory sensation, called an aura, before the onset of a seizure. Epilepsy is not a progressive disorder.
3.10 Electroencephalography (EEG)
Diagnosis of a seizure disorder relies primarily on a person's description of the frequency and type of seizure experienced. Electroencephalography (EEG) may also be performed to help detect abnormal electrical discharges from the brain and to locate the specific area from which they originate. A variety of other diagnostic procedures and laboratory tests may aid this process. Therapeutic management of seizures includes use of anticonvulsants and, where appropriate, surgical intervention.
4.1 Refraction of Light Rays
As light rays pass through the eye, they are refracted by certain eye structures so that they focus to form a clear image on the retina. Sometimes defects of the refractive media interfere with visual acuity, that is, the sharpness of visual perception. These defects include irregularities in the curvature of the cornea, the focusing power of the lens, and the length of the eye.
4.2 Astigmatism
Astigmatism is an abnormal condition in which light rays cannot come to a single point of focus on the retina because of irregular curvature of the cornea or lens. The condition usually can be treated with glasses or contact lenses that correct the refractive error.
4.3 Hyperopia
In hyperopia, also called farsightedness, the rays of light entering the eye are brought into focus at a point behind the retina. This causes the perceived image to appear blurred. Hyperopia occurs when the lens lacks adequate focusing power or the eyeball is too short.
4.4 Myopia
Refractive error is the most common visual problem and myopia, or nearsightedness, is the most frequently occurring type of refractive error. Causes of myopia include elongation of the eyeball and excessive deflection of light by the refracting media such that the rays are focused in front of the retina. This condition interferes with visual acuity, producing a blurred or fuzzy image.
4.5 Refractive Eye Surgery (LASIK)
Using corrective lenses, either in the form of glasses or contact lenses, typically alters refractive errors. In recent years, refractive surgical procedures, such as radial keratotomy in which a series of small incisions are made in the cornea to correct for myopia, have become increasingly popular. Photorefractive keratectomy, or LASIK (seen in the illustration), uses an excimer laser to reshape the cornea.
4.6 Disorders of the Eye
Disorders of the eye have a variety of causes and a range of specific effects. Infection and inflammation commonly affect the structures of the eye, disrupting their sight-producing or protective functions. Impairment of the ocular muscles can interfere with the synchronous movement of the eyes. Trauma, systemic illness, certain medications, and the process of aging can cause damage or deterioration to the eye and threaten the loss of vision.
A hordeolum, or sty, is produced by a bacterial infection of the sebaceous glands of the eyelid. The affected area of the lid becomes red, swollen, and tender (Fig. A). Examples of other inflammatory conditions affecting the eye include conjunctivitis, affecting the conjunctiva (Fig. B); keratitis, affecting the cornea; iritis, affecting the iris; and dacryocystitis, which affects the lacrimal sac. Treatment of these disorders involves administration of oral and topical medications.
4.7 Retinal Damage
Several visual disorders are characterized by damage to the retina. Three of these, which we'll now consider, are glaucoma, diabetic retinopathy, and retinal detachment.
4.8 Development of Glaucoma
Normally there is a balance between the production of aqueous humor and its outflow through the eye's filtration structures at the junction of the iris and cornea. In glaucoma, outflow of the aqueous humor is blocked, causing an increase in intraocular pressure (IOP). Glaucoma may occur as a primary disorder or may develop secondary to systemic illness or trauma.
4.9 Glaucoma
Blockage of the outflow channels for aqueous humor may happen suddenly, causing acute glaucoma, or may progress at so slow a pace that the loss of vision is not recognized until it becomes extensive. Acute glaucoma is a medical emergency; it is accompanied by extreme ocular pain, blurred vision, a red discoloration of the eye, dilation of the pupil, and, possibly, nausea and vomiting. Chronic glaucoma may produce no symptoms initially. Eventually, headaches, blurred vision, and eye pain may be present, in addition to the loss of peripheral vision.
4.10 Treatment for Glaucoma
Conservative treatment for glaucoma involves the use of eyedrops (miotics) to improve drainage of aqueous humor and to decrease its production. If conservative treatment fails, a surgical procedure called trabeculectomy may be used to modify the outflow channels or to create a new opening for the escape of aqueous humor from the anterior cavity, as shown in the illustration.
4.11 Diabetic Retinopathy
Diabetic retinopathy is a complication of diabetes mellitus affecting the blood vessels of the retina. The disorder, which usually occurs in those with poorly controlled diabetes, is characterized by dilation of the retinal capillaries; microaneurysms of the capillary walls; small hemorrhages; leakage of protein from the retinal vessels; and the formation of new blood vessels and connective tissue. The loss of vision associated with diabetic retinopathy may be caused by scarring following the development of hemorrhages, edema resulting from fluid leakage, or the rupture of the new blood vessels, which bleed into the vitreous.
Methods of treating diabetic retinopathy include photocoagulation, i.e., use of a laser to seal leaky blood vessels and to prevent the growth of new ones and injection of a saline solution to replace vitreous humor in which blood and scar tissue have accumulated.
4.12 Retinal Detachment
Retinal detachment is a separation in the layers of the retina. As the separation becomes complete, fluid accumulates between the layers and blindness results. Detachment of the retina may occur suddenly, as in the case of trauma, or slowly, such as when the vitreous shrinks during aging and pulls on the retina, producing retinal tears.
4.13 Image as Seen With Detached Retina
Symptoms of a detached retina include flashes of light, floating spots or opacities, or a ring in the field of vision. As the loss of sight progresses, a sensation of a curtain being drawn across the field of vision may occur.
4.14 Repair of Retinal Tears
Repair of retinal tears is accomplished with photocoagulation and cryotherapy, a procedure in which a freezer burn is used to create scar tissue that seals holes in the eye's innermost layer. Most retinal detachments are treated with a technique known as the scleral buckling. This method involves placing a silicone band over the detached area, forcing the layers of the retina together.
4.15 Cataract
A cataract is a progressive, abnormal condition of the lens characterized by a loss of transparency. Most cataracts are produced by degenerative changes that accompany the aging process; however, cataracts may be congenital or may be caused by trauma, certain medications, infection, or other diseases. The condition leads to a gradual blurring of vision, as the lens clouds over, and an eventual loss of sight. Cataracts are now commonly treated with surgical removal of the lens. An intraocular lens (IOL) is usually implanted in the eye at the time of cataract removal. If an IOL cannot be implanted, external lenses—glasses or contact lenses—must be worn.
4.18 Disorders of the Ear
The ability to hear can be compromised by a variety of diseases and disorders. These pathologic conditions are categorized as problems affecting the external ear, problems of the middle ear, and problems of the inner ear. In this lesson, we'll focus on middle and inner ear disorders.
4.19 Acute Otitis Media
The structure of the eustachian tube and its connection to the nasopharynx causes the middle ear to be prone to infection, or otitis media. Acute otitis media is a common childhood disease associated with colds, sore throats, and blockage of the eustachian tube. Sudden in onset and short in duration, it is caused by a variety of bacteria. Acute otitis media is characterized by a sense of fullness in the ear, diminished hearing, pain, and fever.
4.20 Otitis Media with Effusion
Recurrent bouts of infection and chronic inflammation can lead to the accumulation of fluid—serous, purulent, or mucoid—in the middle ear. Obstruction or dysfunction of the eustachian tube and enlarged lymphoid tissue in the nasopharynx are among the causes of improper fluid drainage. Antibiotic therapy is used to treat acute and chronic otitis media. Surgical incision of the tympanum to relieve the pressure and buildup of fluid may be required for those who don't respond to antibiotic treatment.
4.21 Otosclerosis
Otosclerosis involves the excess formation of bony tissue in the labyrinth that attaches to, and prevents movement of, the stapes. This stiffening of the stapes results in its inability to transmit sound vibrations to the inner ear, producing a conductive hearing loss. The condition is corrected by surgically removing the stapes and replacing it with a prosthesis.
4.22 Vestibular Labyrinth Disorders
We learned in the previous lesson that the structures responsible for equilibrium and balance are housed in the labyrinth of the inner ear. Ménière's disease affects the vestibular labyrinth and can lead to profound hearing loss. The cause of the disease is unknown, but it results in an accumulation of endolymph in the membranous labyrinth. Ménière's disease is marked by vertigo —a sensation that the body is spinning or that objects are spinning around the body. Tinnitus, a subjective noise such as ringing, buzzing, whistling, or clicking—heard in the absence of sound—is another symptom of Ménière's disease. Various methods are used to treat this disorder, including tranquilizers, antihistamines, diuretics, and surgery to reduce the pressure of the endolymph on cochlear hair cells.
4.23 Otoscopy
A variety of techniques can help to detect hearing loss. Screening of auditory function begins with a physical examination of the ear. Otoscopy is the visual inspection of the structures of the outer and middle ear with a hand-held, lighted magnifying device called an otoscope. A pneumatic attachment to the otoscope allows evaluation of the eardrum's mobility.
4.24 Audiometry
Audiometry evaluates hearing acuity and helps to establish the degree and severity of hearing loss. An audiometer is an electric device used to measure the sensitivity of hearing by delivering a series of acoustic tones that range from very low to very high frequencies. The listener signals when the tone is perceived and the results are plotted on a graph called an audiogram. Examination of David's hearing revealed good auditory acuity.
5.1 Threaded Case Study: David Goldman
After asking David questions to test his attentiveness, speed of response, and recall of events, the neurologist decided to refer David for neuropsychological testing. Before we look at the next category of disorders, let's join David as he responds to a number of test questions from the neuropsychologist.
The neuropsychologist notices that David is having difficulty with attention and concentration, short-term memory, judgment, and speed of processing information. She also noticed that David seems to have little energy and a depressed mood. She will forward these findings in a report to David's doctor.
5.2 Psychology
While we're in the neuropsychologist's office, let's take a moment to become familiar with some of the terms from this discipline. These terms, as you'll quickly recognize, are built from word parts. Neuropsychology is a specialty within the field of psychology, the study of mental processes and behavior. The psychologist is an important member of the mental health care team.
To become qualified as a psychologist, one earns a master's or doctoral degree in psychology, not a medical degree. He or she develops an understanding of the personality and mental functions and learns to assess these functions and behaviors by administering psychologic tests.
5.3 Psychiatry
As you'll recall from Module 2, psychiatry is the branch of medicine that seeks to understand and describe human behavior and to treat impaired mental and/or emotional functioning.
Psychiatrists are medical doctors who are trained to recognize, diagnose, treat, and prevent mental disorders. As part of the practice of their specialty, psychiatrists appraise the symptoms associated with psychiatric illness, prescribe and monitor medication, engage in treatment sessions with the patient, called psychotherapy, and participate in treatment planning with members of an interdisciplinary mental health care team. Psychoanalysis is one type of therapeutic method; it involves a long-term, intense interaction between a psychiatrist and a client.
Psychopathy, disease of the mind, can be divided into many descriptive categories. Two such classifications are indicated by the terms neurosis, an emotional disorder characterized by anxiety and ineffective coping ability, and psychosis, severe mental disturbance in which the ability to recognize reality and to interact with one's surroundings is defective or lost.
5.4 Anxiety Disorders
Let's consider some of the disorders in which anxiety is the most prominent feature. Anxiety disorders take many forms.
Panic disorder is characterized by recurrent panic attacks, discrete periods of intense anxiety that occur unexpectedly with no apparent cause in the immediate environment. During the panic attack a person may exhibit a variety of symptoms including shortness of breath, sweating, trembling, palpitations, nausea, blurred vision, and a sense that death is approaching.
5.5 Phobias
The combining form phob/o and the suffix -phobia mean fear; phobic means pertaining to fear.
Phobic disorders involve excessive and unreasonable fear of a particular object or situation. The person with a phobic disorder experiences marked anxiety about encountering the feared object or situation and will go to extreme lengths to avoid it. Some examples of phobia include zoophobia, a fear of animals and insects; acrophobia, a fear of being in high places; and claustrophobia, a fear of small, enclosed places.
Using word parts from this module, can you create a term that means fear of spiders?
5.6 Post-Traumatic Stress Disorder
Yes. You were right if you said that arachnophobia is the term for abnormal fear of spiders.
A person with post-traumatic stress disorder (PTSD) develops symptoms of anxiety and avoidance following a traumatic event. The causal event, an example of which is military combat, is outside the range of normal human experience and induces feelings of terror and helplessness. Other traumatic stressors that may result in PTSD include physical disasters and experiences of physical or sexual abuse.
5.7 Obsessive-Compulsive Disorder
Obsessive-compulsive disorder (OCD) is another psychiatric condition with anxiety as its most prominent feature. An obsession is a persistent, intrusive thought that cannot be dispelled by means of reason or logic. For example, a person who suffers from obsessive thoughts may have an exaggerated fear of contracting an illness. In response to that obsession, he or she may feel compelled to repeatedly perform an action, such as frequent hand washing, to lessen the likelihood of contamination. Although the person may recognize that the behavior is excessive, sometimes significantly interfering with normal routine, the compulsion must be performed to relieve distress.
5.8 Mood Disorders
The complex of associated symptoms and the pattern of episodes define mood disorders. Generally, these disturbances fall into two main categories: bipolar disorder and depressive disorder.
Bipolar disorder is characterized by episodes of both mania —extreme excitement—and depression. These phases alternate with one another or may appear simultaneously. Symptoms observed during a manic episode may include agitation, irritability, inflated self-esteem, distractibility, and a decreased need for sleep. During the depressive phase of bipolar disorder, feelings of sadness, hopelessness, loneliness, and worthlessness may emerge, accompanied by social withdrawal and a lack of interest in normal activities.
5.9 Schizophrenia
The term schizophrenia refers to a group of disorders that share characteristic symptoms, particularly disordered thought processes. This disorganized thinking leads to difficulty in communication and in interpersonal relationships. Schizophrenia is a psychotic disorder; consequently, a person with schizophrenia experiences gross impairment of reality testing and may experience both auditory and visual hallucinations.
5.10 Personality Disorder Clusters
Personality disorders are enduring, pervasive, inflexible, and maladaptive patterns of perceiving and thinking about the world and one's relatedness to it. Explanations for the causes of personality disorders range from having insufficiently or incompletely negotiated the tasks at a particular developmental stage to impaired neurologic functioning.
Personality disorders are organized into three clusters: Cluster A, the odd or eccentric disorders, an example of which is paranoid personality; Cluster B, the dramatic and emotional disorders, an example of which is antisocial personality; and Cluster C, the disorders characterized by anxiety and fear, exemplified by dependent personality disorder.
5.11 Threaded Case Study: David Goldman
The results of David's diagnostic testing suggested two possibilities, both of which proved to be true. David's lack of energy, low mood, and some of his difficulty with concentration and memory were deemed attributable to mild depression. Beyond that, however, his loss of cognitive ability was accounted for by a diagnosis of early onset Alzheimer disease. His physicians believe that David became depressed on realizing his increasing mental impairment. While Dr. James explains the degenerative nature of this disorder, David and his wife come to understand that Alzheimer disease has serious implications for David's life at work and at home. The neurologist has recommended a new drug for pharmacologic management of the disorder, but David and Fran recognize that the drug will not alter the eventual course of the disease. Together with Dr. James they'll plan to maintain David's functional ability for as long as possible. They will look to community resources and Alzheimer disease groups to provide the emotional support that will prove so important.
Introduction
In this module, you will learn more about the medical terms associated with the skin and its accessory organs, which together are known as the integumentary system. When you complete this module, you should be familiar with terms that describe the structures and functions of this system. You should have a good understanding of terms that specify disorders affecting the skin, and you should be able to recognize terms for tests and procedures that are used to diagnose and treat diseases and disorders of the integumentary system. As you work through this module, you may need to refer to the basics of word structure that were introduced in Module 1.
This integrated learning program is intended as a supplement to your text—not as a substitute. Be sure to keep your text available for ready reference.
Objectives
In this module, you will learn to:
- List five functions of the skin.
- Match the epidermis, dermis, and adipose tissue with their characteristics.
- List the four accessory skin structures and describe their functions.
- Write the meaning of the word parts associated with the integumentary system and use them to build and analyze terms.
- Match different types of skin lesions with their descriptions.
1.1 Threaded Case Study: The Integumentary System Components
The skin, the outer covering of the body, is a remarkably complex organ. Tough yet supple, this membrane protects the underlying structures of the body, contains receptors for sensation, and helps to maintain body temperature. It provides a palette for the expression of our emotions and helps define our individual identity. The skin and its accessory organs—the hair, nails, and glands—are known as the integumentary system.
As we begin to learn about the skin and its structures and functions, let's meet Dina Matthews. Dina has been referred by her physician to Dr. Daniels, a dermatologist, for further assessment of a skin growth. Dina and Dr. Daniels will review her health history, patterns of hygiene, lifestyle practices, and risk factors in relation to the development of her dermatological condition. Let's familiarize ourselves with the structures of the skin.
1.2 Layers of the Skin
The skin is a multilayered organ. It consists of a thin outer, avascular layer—the epidermis—and a deeper, dense layer of connective tissue called the dermis. Beneath the dermis is the subcutaneous tissue, a spongy, porous layer with a rich blood supply and a wealth of fat-producing cells.
|
|
|
1.3 Word Parts Pertaining to Skin
The combining forms cutane/o, derm/o, and dermat/o, and the suffix -derm, are all defined as skin; their inclusion in a medical term tells us that the word refers to the integument.
For instance, dermatology is the study of the skin, and a specialist in the field is a dermatologist.
Adding prefixes to the combining forms specifies the layer of the skin to which we're referring. We know from earlier modules that the prefixes sub- and hypo- can both mean under or beneath or below. Thus, we can see that the layer beneath the dermis is subcutaneous. The prefix epi- means on, upon, or over; thus, the epidermis is over the dermis.
1.4 Primary Germ Layers of Skin
The skin is one of the earliest organs to develop, forming during the third week of gestation. After undergoing repeated division, the fertilized egg organizes into three primary layers of cells—the ectoderm, the mesoderm, and the endoderm.
The prefix ecto-, you'll recall from a previous module, means outside; meso- is defined as middle; and endo- as inside. Knowing how these prefixes are defined, you can probably guess that the ectoderm is the outermost primary tissue layer, the mesoderm is the middle layer, and the endoderm is the inner layer of developing cells. The epidermis and the skin's accessory organs arise from the ectoderm.
1.5 Epidermis
The outer skin layer, the epidermis, is composed of several layers or strata itself. The most superficial layer consists of thin, flat, scalelike cells that are continually being shed and replaced by new cells generated at the deepest level of the epidermis. This outermost layer is the stratum corneum.
New skin cells form at the lowest level of the epidermis and migrate toward the outermost layer where they shrink, flatten, and die; their cytoplasm is replaced by a hard, water-repellent scleroprotein called keratin. You should recognize scler/o as the combining form that means hard. The combining form kerat/o, when used in reference to the skin, means horny tissue or hard.
The process of cell change that forms the stratum corneum is called keratinization or keratogenesis. This membrane of cells at the skin's surface becomes thick and chemically resistant, preventing excessive loss of water, salts, and heat from the body. As a result, the skin is better able to protect us against a range of environmental threats, including harmful toxins, invading microorganisms, and physical trauma. For these reasons, the stratum corneum is sometimes called the barrier layer of the skin.
The keratinized cells, also known as horny cells, are eventually sloughed off of the skin's surface and replaced by the migration of new cells.
1.6 Dermis
The dermis, also known as the corium, accounts for most of the skin's mass. It consists of two layers of fibrous tissue that enable the skin to stretch and rebound. The dermis contains blood vessels, nerves, lymphatic vessels, muscle fibers, and hair follicles.
The dermis is also the location of the sebaceous glands and the sweat glands. Sebaceous glands secrete the oily substance called sebum that lubricates the hair and inhibits bacterial growth on the skin.
The receptor endings of nerves within the dermis allow us to sense pain, pressure, touch, and temperature. The blood vessels in the dermis play a critical role in the regulation of body temperature.
1.7 Subcutaneous Layer
The subcutaneous tissue anchors the dermis and the epidermis to the underlying muscle and bone. The nerves and blood vessels that supply the skin run through the subcutaneous layer, which is composed of loose connective tissue filled with fat cells.
These deposits of fat within the subcutaneous tissue are the reason we also refer to this stratum as the subcutaneous adipose layer. The term adipose incorporates the combining form adip/o, which means fat, and the suffix -ose, which in this context means full of or pertaining to.
The production and storage of fat in the subcutaneous layer creates a cushion for the skin and insulates the body against excessive heat loss.
1.9 Hair
Now let's look at some of the accessory structures of the skin.
Hair is an outgrowth from the skin of flexible, keratinized fibers. It covers most of the body except the palms of the hands, soles of the feet, and parts of the external reproductive organs. Formed at the junction of the epidermis and dermis, hair provides protection to delicate body structures. Two combining forms—trich/o and pil/o—mean hair.
Each fiber of hair consists of a root and a shaft; the root is embedded within a saclike structure known as the hair follicle. In a manner that parallels the development of new skin cells, hair is formed from cells at the base of the follicle that push upward to create the visible portion of the hair, the tightly woven network of horny cells that is the hair shaft.
1.10 Nails
Nails are hard, flat plates of keratin that cover the tips of the fingers and toes, protecting them from injury. At the base of each nail, hidden by a fold of skin called the cuticle, lies the nail root. The white crescent-shaped area nearest the root is called the lunula; it marks the site of nail growth.
The combining forms for nail are onych/o and ungu/o. Combine the first one with the prefix para-, which means near or beside, and you get paronychium, the soft tissue that surrounds the nail border.
Using the second combining form, the term ungual means pertaining to the nail. For example, ungual tuft is the term for the end portion of the distal phalanx that lies under the nail.
1.11 Sebaceous Glands
Sebaceous glands and sweat glands form the third category of the skin's appendages.
Sebaceous glands secrete sebum, an oily substance that lubricates the skin and hair. Sebum also prevents excessive water loss from the skin and, because of its acidic nature, helps to protect against infection. Found in the dermal layer of the skin, in close association with hair follicles, sebaceous glands are most numerous on the scalp, face, back, and upper chest.
1.12 Sudoriferous Glands
The sweat glands are also called sudoriferous glands. Perspiration produced by these glands helps to regulate body temperature through the cooling process of evaporation. Perspiration also rids the body of waste products and moisturizes the surface cells of the skin. The combining form for sweat is hidr/o.
Some sudoriferous glands are associated with hair follicles and excrete sweat directly from the follicle. Others secrete sweat through pores, tiny openings on the surface of the skin.
A type of gland that is found in the skin, breast, eyelid, and ear is the aprocrine gland. Apocrine glands in the breast secrete fat droplets into breast milk and those in the ear help form earwax. Apocrine glands in the skin and eyelid are sweat glands. Most apocrine glands in the skin are in the armpits, the groin, and the area around the nipples of the breast. Apocrine glands in the skin are scent glands, and their secretions usually have an odor. Another type of gland (eccrine gland or simple sweat gland) produces the most sweat.
1.13 Skin Pigmentation
Before we conclude this lesson, let's review some word parts and terms used to refer to skin color. These terms describe variations in skin color related to racial and ethnic differences as well as alterations in skin color that are associated with certain conditions or disorders.
You'll recognize some of these descriptors from Module 4. For example, you probably recall that melanocytes are special cells in the epidermis that contain the black pigment melanin. As you can see, the terms melanocyte and melanin include the combining form melan/o, which means black.
The amount of pigment produced by the melanocytes determines the color of the skin. Melanin also serves to filter, and thus provides protection from, ultraviolet light.
Albinism, a condition about which we'll learn more later in this module, involves a lack of melanin.
|
|
|
1.14 Skin Coloration as Indicator of Health or Illness
Specific terms are used to describe skin color as an indicator of health or illness. These include erythema (Fig. A), which refers to redness of the skin often associated with inflammation; xanthosis, defined as an abnormal condition of yellow, which is manifested as the symptom of jaundice (Fig. B); and cyanosis (Fig. C), a bluish color of the skin indicative of oxygen deficiency. You can recognize in these terms some familiar combining forms: erythr/o, which means red; xanth/o, meaning yellow; and cyan/o, defined as blue.
1.15 Threaded Case Study: Dina Matthews
Having completed the health history, Dr. Daniels now proceeds with a physical examination, which will include a thorough assessment of the skin and its appendages.
1.1 Skin Biopsies
You will recall from previous lessons that a biopsy is a procedure in which a sample of living tissue is removed from the body and examined microscopically to provide a diagnosis. The abbreviation for biopsy is bx.
There are several methods for performing skin biopsies, and most can be done on an outpatient basis. The method chosen is determined by the type, size, and location of the lesion being investigated. All methods involve the use of a local anesthetic either applied topically or injected into the area of the lesion.
The least invasive technique, called a shave biopsy, involves the removal of superficial levels of skin. This type of biopsy does not create a wound that requires sutures.
Curettage (Fig. A) also involves removal of a superficial level of cells. In this type of biopsy, material is scraped from the lesion using an instrument called a curette.
An aspiration biopsy involves entering the lesion with a thin needle attached to a syringe. Liquid and/or cells from the lesion are then drawn up into the syringe for examination.
Punch biopsies (Fig. B) involve removal of a small cylinder of skin, usually about the size of a pencil eraser, using a sharp hollow instrument. The area may require closure with stitches, depending on the size of the sample taken.
An excisional biopsy involves removal of the entire lesion. Using an injected local anesthetic, the entire lump, spot, or sore is removed, going as deep as necessary to get the entire area. The incision is then closed with stitches.
1.2 Laboratory Cultures
Perhaps you recall from Module 11 that a culture is a laboratory procedure for growing microorganisms. Samples of potentially infected body fluids are placed in a sterile nutrient medium, called agar, and incubated to create a colony of the infecting organisms. Microbes from this culture are then placed on microscope slides where they may be examined directly or stained to aid in identification.
A new agar plate (petri dish) may then be inoculated with organisms from the first culture, and tiny disks impregnated with various antibiotics are also placed on the agar plate. Since bacteria will not grow near the disks of those substances that are effective in killing them, this test provides useful information as to what medications are likely to provide effective treatment.
1.3 Wood's Light Examination
A Tzanck test is a microscopic exam of lesions for the purpose of diagnosing herpes zoster and herpes simplex. A Wood's light examination identifies a variety of skin infections through the use of ultraviolet light filtered through a black light (Wood's glass); tinea capitis and pseudomonas infections in burns are two of the disorders the test can reveal.
1.4 Skin Tests
Skin testing can often help to identify the causative agent in eczema. This method of diagnosing a suspected sensitivity is performed in a number of ways. In a patch test, a piece of gauze or filter paper containing an allergen extract is applied to the skin to see if it produces a reaction. In the scratch test, a small quantity of a solution containing an allergy-causing substance is placed on a lightly scratched area of the skin. An intradermal injection may also be used, in which a suspected allergen is injected into the skin to assess sensitivity.
1.5 Sweat Test
Bacterial analysis is a general term for culture and serology of lesions to help diagnose such disorders as impetigo. In the case of wounds, ulcers, or abscesses, the lab samplings are specifically identified as such—that is, as wound and abscess cultures.
Fungal tests are cultures of lesion scrapings used to identify dermatophytoses, such as the various forms of tinea, whereas a viral culture is a sampling of vesicular fluid for the purpose of identifying viruses. Sweat tests (as seen in the illustration) analyze the perspiration of individuals for signs of abnormally high levels of various minerals, such as sodium and chloride (present in the perspiration of persons with cystic fibrosis).
2.1 Threaded Case Study: Effects of Sun Damage
Remember Dina? Throughout her life, her recreational and work activities have enabled her to spend a good deal of the time outdoors. How might this affect her skin?
As the surface barrier to the external environment, the skin often reflects the results of its protective function. Exposure to sun, radiation, chemicals, microorganisms, and other environmental hazards can cause specific changes in the health and appearance of the skin.
Pressure, friction, and shearing forces can also weaken and damage the skin. In addition, the integument serves as a lens through which alterations to other body systems may be seen. As we'll eventually learn, Dina's skin condition is partly the result of an environmental factor.
2.2 Threaded Case Study: Primary, Secondary Lesions
Dina points out to Dr. Daniels that she is concerned about a small bump on her nose. This small bump is a type of lesion. A lesion is a pathologic alteration in body tissue caused by injury or disease. Lesions assume a variety of forms, depending on the specific cause of tissue damage. Primary lesions are those that arise from normal skin as the result of a pathologic process; secondary lesions develop from changes—for example, erosion—to the primary injury. The tissue damage associated with lesions is usually described in terms of its color, size, location, pattern, and distribution on the body.
2.3 Cyst, Vesicle, Bulla
A cyst is a closed, thick-walled sac that contains fluid or semi-solid material. It is a primary lesion that typically forms in response to a parasitic infection or obstruction of a duct or gland.
Vesicles—small, circumscribed elevations on the skin that contain serous fluid—are another type of primary lesion. These lesions, also known as blisters, may vary from a few millimeters to a centimeter in diameter; vesicles larger than 1 centimeter are called bullae (sing., bulla). Vesicles may form following burn injuries; they are also associated with disorders such as chickenpox and allergic contact dermatitis.
2.4 Pustule, Abscess
Pustules are similar to vesicles in that they are small, elevated, superficial lesions. Instead of serous fluid, however, these lesions contain pus—the thick, yellowish, leukocyte-containing fluid produced by tissue death. Pustules are often the result of infection and inflammation of a hair follicle or sweat pore.
An abscess is a pus-filled cavity surrounded by inflamed tissue that forms in response to a localized infection. The terms purulent, suppurative, and pyogenic are all used to refer to fluid-filled lesions that produce or contain pus.
2.5 Macule
A macule is a flat, circumscribed area of discoloration on the surface of the skin. Macules are usually less than a centimeter in diameter and may vary in color. Freckles and flat moles are examples of this type of primary lesion.
2.6 Wheal, Plaque
A wheal is an irregularly shaped, solid elevation of the skin. The area of eruption is often more red or pale than the surrounding skin and may produce severe itching. A wheal is the type of primary lesion that forms following many insect bites and in response to certain allergens.
The term plaque describes a solid, elevated lesion that is greater than 0.5 centimeters in diameter. The skin alterations associated with the inflammatory disorder psoriasis, which we'll learn more about shortly, are plaques.
2.7 Papule, Nodule
A papule is a small, solid, raised skin lesion that is less than 1 centimeter in diameter. Papules develop as one of the signs of infectious diseases, such as chickenpox, measles, and smallpox, or as a hypersensitivity reaction to drugs. Larger papules are called nodules. Dina's physical examination has revealed a nodule on the tip of her right nostril.
2.9 Ulcer
Now let's look at some secondary skin lesions. An ulcer is a concave open sore of the skin or mucous membrane that results from the sloughing off of infected dead tissue. Ulcers may be caused by trauma or unrelieved pressure to an area of the skin. Ulcers may evolve from atrophy, a depression in the skin resulting from thinning of the epidermis or dermis. They may occur as a complication of vascular problems, in association with specific illnesses, or, as in the case of gastric ulcers, following prolonged exposure to an acidic substance.
2.10 Fissure
Cracklike lesions of the skin are known as fissures. These grooves in the epidermis may be caused by trauma, infectious disease, or systemic disorders.
A crust, also called a scab, is a collection of dried serum and cellular debris on the skin's surface. Scales are thin flakes of shedding, keratinized epidermal cells, one example of which is dandruff.
2.11 Keloid
A keloid is a lesion that arises from an overgrowth of tissue at the site of a wound. The tissue that forms—a rounded, firm, and irregular elevation—exceeds the requirement for normal repair and healing. The tissue that develops during the process of normal healing is known as a scar.
2.12 Vascular Lesions
Next we'll describe two types of vascular lesions—pathologic skin changes that occur in response to vessel wall destruction or defects. Petechiae (as seen in the illustration) are reddish-purple pinpoint spots that appear on the skin as a result of intradermal hemorrhaging caused by injury, inflammation, or the spontaneous leakage of blood from fragile vessel walls.
Larger areas of discoloration caused by bleeding and collection of extravascular blood beneath the skin are known as ecchymoses, also called bruises, or blue-black marks.
2.13 Threaded Case Study: Dina Matthews
Dina is eager to hear what Dr. Daniels has concluded about the lesion on her nose. She remembers being asked about other characteristics of the nodule; it's not painful, it doesn't itch, and it has gradually gotten somewhat larger over time. Dina has also noticed a slight ulceration that is new. She hadn't considered the nodule a serious problem, but she is concerned that it is becoming more noticeable and she wants it removed.
3.1 Pathologic Alterations of the Skin
Pathologic alterations of the skin and its appendages may be the consequence of specific disorders of the integument or may reveal an underlying disease state. Abnormalities may occur in relation to the appearance, texture, moisture, temperature, resilience, and mobility of the skin; the size, shape, thickness, and opacity of the nails; and the amount, texture, color, and distribution of hair.
3.2 Pruritus, Urticaria
Pruritus, or itching, is a symptom associated with many dermatologic disorders. It is an uncomfortable cutaneous sensation that elicits the urge to scratch. Pruritus is caused by repeated stimulation of the same nerve fibers within the skin that sense pain. Common causes of itching include dry skin, skin irritants, infectious diseases, allergic reactions, and systemic disorders. Urticaria, seen in the accompanying illustration, is characterized by the eruption of edematous wheals. It is an example of an allergic reaction in which pruritus is a prominent symptom.
3.3 Xeroderma
You'll recall that the combining form xer/o means dry. Xerosis is a condition of dry skin that results when the epidermis lacks moisture or sebum. It is characterized by a pattern of fine lines, scaling, and pruritus. Causes of dry skin include low humidity, excessive bathing, and the decreased production of sebum that accompanies the aging process. Xeroderma is a chronic skin condition manifested by dryness and roughness. Xeroderma is a mild form of ichthyosis, a group of cutaneous disorders characterized by the formation of dry patches of skin that resemble fish scales.
3.4 Scleroderma
Scleroderma, hardening of the skin, is a chronic, progressive disorder of the connective tissue. The degenerative changes associated with the disease can involve the skin, blood vessels, skeletal muscle, and internal organs. As part of the disease process, collagen—the protein fiber that gives the skin its strength—is overproduced. As a result, the skin loses its elasticity and becomes thick and taut. Scleroderma has no known etiology, although systemic spread of the disorder may be linked to an autoimmune dysfunction.
3.5 Discoid Lupus Erythematosus (DLE)
Discoid lupus erythematosus (DLE) is another chronic disorder, primarily of the skin, one cause of which may also be autoimmune dysfunction. The lesions of DLE are well-defined and erythematous with an atrophied center and a scaly border. They are typically distributed on the face but may also appear on other parts of the body or extend into the hair. It occurs most often in women, in the third and fourth decades of life, and may be precipitated by physical trauma or stress. DLE is treated with the use of topical and systemic medications.
3.6 Vitiligo, Albinism
For a variety of reasons, localized loss of skin pigmentation can occur. This condition, known as vitiligo, may be genetic or acquired and is usually chronic and progressive. It is characterized by milk-white patches surrounded by areas of normal pigmentation. Although its cause is unknown, vitiligo is associated with certain disorders of the endocrine system, with some types of infectious disease, and with exposure to specific chemical and pharmacologic agents. Albinism, built from the combining form albin/o, meaning white, is an inherited deficiency or absence of pigment in the skin, hair, and eyes caused by an abnormality in melanin production.
3.7 Eczema
One of the most common forms of skin disease is dermatitis—a term constructed from the word parts dermat/o and -itis, meaning inflammation of the skin.
Eczema, seen here, is the most common inflammatory disorder of the skin. An eczematous dermatitis may result from an external irritant—a fabric, chemical, plant, metal, or organism—or may occur because of a constitutional or predisposing genetic influence. No matter what the specific cause, eczema is expressed as a breakdown of the epidermis, with eruption of erythematous, pruritic vesicles.
3.10 Acne
Because the skin is the vehicle for our physical presentation to the world, abnormal conditions of the integument have implications for our emotional well-being as well as for our physical health. Acne, a common skin disorder seen in 80% of adolescents, is one such disorder. It is a common inflammatory disease that typically begins during puberty but can have an adult onset and continue throughout the adult years.
The lesions that characterize acne—papules, pustules, nodules, and cysts—form when sebum, cell debris, and bacteria combine to obstruct the pores. A blackhead develops when the pore is partially obstructed; whiteheads form when the pore is completely blocked.
3.11 Dermabrasion
Acne usually affects the face and neck, the upper chest, and back. Although the cause is unknown, development of acne is associated with endocrine disorders, food allergies, stress, and infection. Heredity may also be a causative factor. Treatments may include the use of topical applications; administration of other medications—for example, antibiotics—to achieve systemic effects; and surgical procedures, such as dermabrasion, shown in the accompanying illustration, to remove scarring.
3.12 Threaded Case Study: Dina Matthews
Because of its appearance, Dina wonders if the small papule on her nostril might be the beginnings of acne or a pimple. However, Dr. Daniels is able to determine that this is not the case. Dina's papule is something else entirely, as we shall soon see.
3.13 Psoriasis
Psoriasis is a chronic inflammatory skin disorder in which thick, scaly lesions form because of an excessive epithelial cell growth rate. The lesions commonly occur on the elbows, knees, scalp, back, and genitalia. The exact cause of psoriasis is unknown, but heredity seems to play a role in this disorder. Infection, some drugs, climate, and stress can trigger an attack of psoriasis.
3.14 Skin Infection
As we learned previously, the skin is the first line of protection against invading pathogens. Thus, despite the antimicrobial effect of sebum, the skin is often the site of infection. Many different microorganisms—viruses, fungi, and bacteria—can cause skin conditions. Next we'll look at two types of skin disorders that result from viral infection.
3.15 Herpes Virus
The term herpes virus actually refers to a group of seven related viruses. Infection caused by the herpes simplex virus (HSV) leads to the formation of painful, fluid-filled lesions—vesicles and blisters—on the skin and mucous membranes (Fig. A). HSV1 infections tend to manifest in the facial area, particularly around the mouth and nose, as shown in the illustration on the left. Herpes zoster, also known as shingles, is caused by the reactivation of the same virus—varicella zoster—that is responsible for the development of chickenpox (Fig. B). The skin eruptions associated with herpes zoster are painful vesicular lesions that follow the route of the spinal or cranial nerves inflamed by the virus. The elderly and persons with compromised immune systems are particularly at risk for contracting herpes zoster.
3.16 Scabies, Pediculosis
Just as the skin's protective function exposes it to the possibility of infection, the integument also may be a site for parasitic infestation. Scabies (Fig. A) is a contagious dermatitis caused by the penetration into the epidermis of the scabies itch mite. The disease, characterized by a papular pruritic rash, is transmitted by direct contact with infected persons. It most commonly affects the webs of the fingers, the flexor surfaces of the wrists, and the thighs.
Another parasitic infection, pediculosis (Fig. B), is an invasion into the skin and hair by lice.
3.17 Seborrhea
Now let's look at some conditions that either develop from, or affect, the accessory structures of the skin, beginning with the sebaceous glands. We know, of course, that sebum offers some protection against disease. But did you know that we can also have too much sebum? An excessive discharge of sebum is called seborrhea (Fig. A). Sometimes the overproduction of sebum results in the formation of scales and crusts on the skin's surface, as is the case in a disorder known as seborrheic dermatitis (Fig. B).
3.18 Hidradenitis
Remember that the combining form hidr/o means sweat? Medical terms containing that word part refer to disorders of the sweat, or sudoriferous, glands. Hidradenitis is an infection or inflammation of the sweat glands. The term hyperhidrosis describes a condition of excessive perspiration, whereas anhidrosis is a disorder characterized by inadequate perspiration.
3.20 Trichosis, Alopecia
Trichosis, a term in which you'll recognize the combining form trich/o, meaning hair, refers to any abnormal condition of hair growth or color. Alopecia (seen in the illustration), a type of trichosis, is the absence or loss of hair from areas where it normally grows, especially from the scalp. The hair loss may be partial or complete, transient or progressive. Loss of hair is associated with normal aging, disease, and injury or may occur as a reaction to certain types of medication or medical treatment.
3.21 Electrolysis
Hair transplantation is a form of dermatologic surgery that uses grafts of hair-bearing tissue to correct scalp hair deficiencies. Electrolysis is a method used to remove unwanted hair, which, as you can probably guess from analyzing the word parts, involves the use of electrical energy to destroy hair follicles.
3.22 Folliculitis
Folliculitis is an inflammation of the hair follicles in response to bacterial infection. The disorder is manifested by the formation of small pustules at the hair follicle opening, with development of crusting. Sites most commonly affected by folliculitis include the scalp, face, and extremities.
3.23 Abnormal Conditions of the Nail
The nail plates and beds of the fingers and toes are affected by a variety of abnormal conditions. You'll recall that two combining forms—onych/o and ungu/o—mean nail; however, most terms describing conditions of the nails are built from the former word part. Onychomycosis (Fig. A) is a fungal infection of the nails that now occurs more commonly because of the increased use of artificial fingernails. Other conditions of the nails include onychomalacia, which is a softening of the nails, and paronychia (Fig. B), a diseased state around the nail. In advanced abnormal conditions, onychectomy, excision of the nail or part of the nail, may become necessary.
4.1 Wounds
Serving its protective function, the skin can suffer many different types of injuries. A wound is any physical injury involving a break in the skin. Wounds usually are caused by an act or accident rather than by disease.
4.2 Types of Wounds
A laceration is a jagged or mangled wound that results from the tearing of body tissue. An abrasion involves the rubbing or scraping away, by friction, of the skin's surface.
4.3 Contusion, Puncture Wound
A contusion is an injury caused by a blow to the skin that does not disrupt the skin's integrity. Contusions are typically accompanied by swelling, discoloration, and pain. Puncture wounds, in contrast to contusions, involve piercing or penetration of the skin by a narrow object, such as a knife or nail.
4.4 Hyperthermia, Hypothermia
Some injuries to the integument are occasioned by extremes of temperature. First, let's review a few terms that describe abnormal variations in body temperature. The combining form therm/o means temperature. By joining the prefix hyper- and the suffix -ia to therm/o, we form the term hyperthermia—an abnormal condition of high temperature. In hyperthermia, the body's normal temperature regulation system is overridden and temperature increases in relation to factors such as a hot environment, illness, or trauma. If we replace the prefix hyper- with hypo-, we create the term hypothermia. Hypothermia is an abnormal and dangerous condition in which the body temperature is significantly decreased, usually in response to cold and/or damp conditions.
4.5 Burns
Perhaps no skin condition is potentially as devastating as a burn injury. A burn is the damage to tissue that results from excessive exposure to heat, electricity, chemicals, or radiation. Burns are generally classified as first degree, involving the epidermis only, as in sunburn (Fig. A); second degree, or partial thickness, involving the epidermis and dermis (Fig. B); and third degree, full thickness, in which all the layers of the skin have been injured (Fig. C).
The treatment of burns includes preventing infection, promoting the integrity of the skin, relieving pain, maintaining a proper fluid balance and good nutrition, and providing emotional support. Debridement, removing damaged tissue, is an important step in the healing process and may be performed in a hydrotherapy bath. Surgical repair of the skin, dermatoplasty, for both burns and cancerous lesions can sometimes involve the use of a skin graft to replace removed, damaged skin.
4.6 Frostbite
Prolonged exposure to cold temperature also can prove extremely injurious to the skin. Like burns, frostbite—the traumatic effect of freezing a body part—is categorized as first, second, or third degree depending on its level of severity. Exposed areas such as the ears, nose, fingers, cheeks, and toes are most often affected. The tissue damage associated with frostbite follows constriction of, and damage to, the blood vessels. As a consequence, circulation is impaired and oxygen supply to skin tissue is diminished. Symptoms include tingling, redness followed by pallor and numbness, formation of vesicles, and, in severe cases, tissue death.
5.1 Neoplasms
Our next category of skin abnormalities are the neoplasms, a name applied to any abnormal growth of new tissue whether it is benign or malignant. Most neoplasms of the skin are benign; that is, they do not invade surrounding tissue or spread to distant sites. Benign skin growths can arise from the epidermis, from sweat or sebaceous glands, or from connective tissue.
Let's look first at a very common benign neoplasm. The term keratosis—which incorporates the combining form kerat/o, meaning horny—describes any lesion that develops as a result of excessive growth, and thickening, of the epidermis. There are several different types of keratoses. Seborrheic keratosis is a commonly observed benign lesion, particularly among the elderly. The neoplasms—well-circumscribed, slightly elevated, pigmented, often covered with an oily crust and pruritic—occur on the face, neck, chest, and upper back.
Actinic keratosis is a thickening of the outer layer of the skin caused by overexposure to the sun. The lesions associated with this condition are erythematous, irregular, and raised, with a rough surface. They are typically found on the face, hands, neck, and arms and are potentially malignant growths.
5.2 Types of Keratoses
Corns and calluses are also examples of keratosis. A corn is a smooth, thick mass that develops from the epidermis of the feet and toes. Corns are caused by constant friction and pressure, the type exerted, for example, by ill-fitting shoes. These growths form on the bony prominences of the foot and between the toes and can be very painful.
Calluses are not as well delineated as corns and are usually not tender. Calluses tend to grow on the weight bearing areas of the feet and on the palmar surface of the hands.
These two are distinguished from a third growth, the verruca or wart, which is a benign tumor of the epidermal layer of the skin. This is a circumscribed, elevated, firm papule caused by a papillomavirus. Warts are generally transmitted by direct contact with the skin of an infected person. They can be removed by a process known as cryosurgery, the application of subfreezing liquid nitrogen to destroy the lesion.
5.3 Furuncle
A furuncle, also called a boil, is a pus-containing growth, formed by inflammation originating in a hair follicle and characterized by pain and redness. Usually, the inflammation develops in response to a bacterial infection, such as a staphylococcal infection.
5.4 Nevus
A nevus, or mole, is a circumscribed, hyperpigmented area of the skin. Most nevi are congenital, but some are acquired; they vary in size, shape, and color. They may be flat, slightly elevated, smooth, rough, or hairy. Because some nevi are dysplastic, potentially cancerous, any change in color, size, or texture must be evaluated carefully.
5.5 Threaded Case Study: Shave Biopsy
A sample of Dina's papule is needed to determine whether it is cancerous and to identify the type of growth. Following her physical exam, a biopsy of her facial lesion, e.g., excision of a portion of the tissue for microscopic examination, is performed to help diagnose the specific problem.
6.1 Skin Cancers
Skin cancers are the most common and the most curable malignancies. Each year more than half a million people in the
Skin cancers are grouped into two basic categories: malignant melanoma, in which the tumor arises from the melanocyte system, and nonmelanoma skin cancer. Malignant melanoma is the most serious of the skin cancers. Melanomas are composed of melanocytes, the cells that produce the pigment melanin. In many instances, these tumors develop from pigmented nevi. These lesions are asymmetric in shape, have irregular borders, are variegated in color, and typically are less than 6 mm in diameter. The most frequent sites of occurrence are the upper back, the lower extremities, the head, and the neck, but the lesions may occur in, or metastasize to, any part of the body. Heredity and sun exposure are risk factors for development of malignant melanoma. Methods of treatment include surgery, chemotherapy, and radiation.
6.2 Kaposi Sarcoma
Kaposi sarcoma is a formerly rare cutaneous malignancy that now is frequently seen in association with acquired immunodeficiency syndrome (AIDS). The disorder is characterized by reddish-purple lesions that initially appear on the lower extremities and gradually spread to the upper body, metastasizing to the lymph nodes and organs. Radiation and chemotherapy are usually recommended for treatment of Kaposi sarcoma.
6.3 Squamous Cell Carcinoma
Squamous cell carcinoma is a cutaneous malignancy that arises from the squamous epithelial cells of the epidermis. It is most often found in sun-damaged skin previously affected by actinic keratosis. The scaly, slightly elevated lesions associated with this condition can metastasize, spreading to other areas of the skin and to regional lymph nodes. Surgery and radiation therapy are used to treat squamous cell carcinoma.
6.4 Basal Cell Carcinoma
Finally, basal cell carcinoma is the most commonly occurring malignant skin condition. It tends to affect those with fair skin and is seen more often in men than women. Tumors associated with this condition, which develop from the basal cell layer of the epidermis, are usually reddish, hard, elevated lesions; they are slow growing and rarely metastasize. The lesions tend to form in sun-exposed areas of the body, such as the face and neck.
6.6 Threaded Case Study: Mohs Surgery
The biopsy of Dina's facial lesion reveals basal cell carcinoma. This finding corresponds with Dina's report, during her health history, of having experienced several severe sunburns in the past while enjoying outdoor activities. Treatment modalities for basal cell carcinoma include cryosurgery, radiation therapy, and microscopically controlled excision of the malignancy. Dr. Daniels recommends Mohs surgery for removal of the lesion, and together they discuss ways to prevent its recurrence.
Module 17
Introduction
In this module, you will learn more about the medical terms associated with the endocrine system. When you complete this module, you should be familiar with terms that describe the structure and functions of this system. You should have a good understanding of terms that specify endocrine disorders, and you should be able to recognize terms for tests and procedures that are used to diagnose and treat diseases and disorders of the endocrine system. As you work through this module, you may need to refer to the basics of word structure that were introduced in Module 1.
This integrated learning program is intended as a supplement to your text—not as a substitute. Be sure to keep your text available for ready reference.
Objectives
In this module, you will learn to:
- List the names of six major glands of the endocrine system.
- Identify the pituitary gland as the master gland.
- Describe two ways in which the pituitary gland cooperates with the nervous system to maintain homeostasis.
- Recognize the hormones associated with the major endocrine organs and their target organs or functions.
- Name one exocrine gland and recognize the difference between it and an endocrine gland.
- Recognize structural and functional aspects of the breasts.
- Write the meaning of the word parts associated with the endocrine system and use them to build and analyze terms.
1.1 Endocrine and Nervous Systems
You'll remember that in Module 15 we described the nervous system as a high-speed information network. Together, the nervous and the endocrine systems keep the body functioning as an integrated whole.
Homeostasis, you'll recall, refers to a constant, balanced internal environment. This term comes from home/o, meaning same, and -stasis, which means control. The combined functions of the nervous system and the endocrine system maintain homeostasis.
In this module, we'll consider how the two systems differ and focus on the particular contributions of the endocrine system. The study of the endocrine glands is called endocrinology.
1.2 Chemical Messengers
Interestingly, both the nervous and the endocrine systems use chemical messengers to affect body processes. Recall that neurotransmitter chemicals in the nervous system travel between cells, triggering the electrical impulses that send signals from one part of the body to another. These signals travel rapidly and tend to have effects that are short-lived.
The chemical messengers of the endocrine system travel through the bloodstream, a much slower route. Thus, the effects of the endocrine system tend to appear more slowly and to last longer.
1.3 Threaded Case Study: Larry
To help us become more familiar with the endocrine system, let's meet Larry. A few months ago, Larry began to notice that he was feeling more fatigued than usual. At first, he thought it was because of the stresses at work. His job in computer support is demanding, and he'd been putting in long hours. Because his work is sedentary, he'd also been gaining weight over the last few years. As he continued to feel tired and began to experience other physical complaints, Larry decided to visit his doctor. Larry's family physician referred him to an endocrinologist, a physician who specializes in diseases and disorders of the endocrine glands. We'll check in with Larry again during that visit.
1.4 Glands of the Endocrine System (animation)
The glands of the endocrine system are widely distributed throughout the body. These include the pituitary, pineal, thyroid, parathyroid, thymus and adrenal glands, the pancreas, the ovaries (in women), and the testes (in men).
Generally, these glands regulate metabolism, the sum total of all the chemical processes that take place in the human body. These processes include the distribution of nutrients to the cells, the generation of energy, and the elimination of wastes. In these ways, the endocrine glands help to maintain homeostasis, the stability of the body's internal environment.
Endocrine glands also play an important role in growth, development, and reproduction.
1.5 Endocrine and Exocrine Glands
Endocrine glands regulate body function by secreting chemicals called hormones that control the activities of other tissues and organs.
The endocrine glands are ductless, which means that there is no tubular portion of the gland through which chemicals pass from the gland after they are secreted; endocrine glands secrete hormones through the glandular membrane directly into the bloodstream. You will recall that the prefix endo- means within. The suffix -crine means to secrete. Thus, endocrine means to secrete within.
By contrast, exocrine glands deliver their secretions through a duct. For example, sweat glands are exocrine glands that excrete perspiration through ducts to the surface of the skin.
|
|
|
1.7 Chemical Structure of Hormones
One helpful way to categorize hormones, and aid our understanding of how they work, is to group them according to their chemical structure.
Chemically, hormones are either proteins or steroids. Proteins are formed from amino acids, and steroids are made from the lipid cholesterol.
The sex glands (the ovaries and testes) and the cortex secrete steroid hormones. The adrenal cortex is the outer portion of the adrenal gland.
All other endocrine glands secrete protein or protein-related hormones.
1.8 Target Tissues and Organs
Hormones work by affecting specific tissues, called target tissues. The target organ or tissue may be near to, or far from, the endocrine gland. A hormone may affect one target organ or many.
1.9 Hormones Bind with Receptors
Hormones interact with target tissues by binding to receptors either on the surface of the tissue's cells or within the cells.
These receptors allow the tissue to "recognize" and respond to specific hormones. The receptor and the hormone are similar to a lock and key. The key, or hormone, must "fit" the lock—the receptor—in order to work.
Protein hormones bind with receptors on the plasma membrane of the target tissue's cells, as seen on the left. Steroid hormones pass through the plasma membrane and bind with receptors inside the cell (seen on the right).
1.10 Hormones Secreted by Other Tissues
In addition to the organs of the endocrine system, there are other tissues that secrete hormones. For example, the mucosal lining of certain gastrointestinal structures has cells that produce the hormone gastrin, which helps to regulate digestion. Specific cells in the wall of the heart secrete a hormone called atriopeptin that causes the kidneys to excrete sodium.
You will recall from Module 13 that the placenta produces hormones during pregnancy. These hormones include human chorionic gonadotropin (HCG), estrogen, and progesterone. These hormones help to maintain the uterine lining during pregnancy.
The prostaglandins are hormonelike substances produced by many of the body's tissues. They stimulate the contraction of smooth muscle, influence the inflammatory response, and are involved in gastrointestinal and vascular functions, including the lowering of blood pressure.
2.1 Pituitary Gland
The pituitary gland, indicated by the combining form pituitar/o, is located in the cranial cavity in a depression of the skull called the sella turcica. The pituitary is also known as the hypophysis or hypophysis cerebri. It is about the size and shape of a pea and is attached to the undersurface of the hypothalamus.
You know that hypo- means under or below and you learned in Module 14 that -physis means to grow. This should help you remember that the pituitary gland grows under the hypothalamus.
The gland consists of two major lobes: the anterior lobe and the posterior lobe.
The anterior lobe of the pituitary is also called the adenohypophysis. It is an upward extension of the pharynx and consists of glandular tissue. Regulating hormones from the hypothalamus stimulate this lobe. It will help you to remember the nature of the anterior lobe if you recall that the combining form aden/o means gland.
The posterior lobe is also known as the neurohypophysis. It is a downward projection of the brain and is composed of nervous tissue. It is stimulated by nerve impulses from the hypothalamus. Note that neurohypophysis contains the combining form neur/o, meaning nerve.
2.2 Hypothalamus
Before we explore the role of the pituitary gland, let's consider its relationship to the hypothalamus. Although technically part of the nervous system, the hypothalamus exerts an important influence on the pituitary gland, its target organ. By secreting both releasing hormones and release-inhibiting hormones, the hypothalamus controls the secretions of the anterior pituitary lobe. Further, the hypothalamus produces hormones that are transported to the posterior pituitary lobe and stored there until needed.
2.3 Hormones Supplied by the Pituitary Gland
The pituitary gland supplies numerous hormones that affect almost every bodily function. Because it influences so many vital processes, the pituitary gland is sometimes called the master gland.
|
|
|
2.5 Growth Hormone
Under the control of the hypothalamus, the anterior lobe of the pituitary gland secretes seven hormones.
Growth hormone (GH), also known as somatotropin (STH), affects the growth of the skeletal muscles and the long bones of the body.
Somatotropin also promotes the synthesis of proteins, performs cell repair, and helps to maintain blood glucose levels.
You will recall that the combining form somat/o means body. The suffix -tropin means stimulating. It is related to trop/o, meaning stimulate, and tropic, meaning pertaining to stimulation. Since the function of hormones is to stimulate, you will find the word parts in the terms for many hormones.
2.6 Prolactin
Prolactin (PRL), also called lactogenic hormone (LTH), is another hormone secreted by the anterior lobe. The combining form lact/o means milk and the suffix -genic means producing.
PRL, in concert with other hormones, stimulates the growth and development of the breasts. It also causes the mammary glands in the breast to produce milk after childbirth.
2.7 Mammary Glands and Lactation
The breasts, or mammary glands, are exocrine glands; they are accessory structures of the female reproductive system that lie on the upper chest between the second and sixth ribs. The combining forms mamm/o and mast/o mean breast.
The primary function of the mammary glands is lactation, the production of nutrient-rich milk for the newborn. Recall that lact/o means milk; the suffix -ation means process.
The breasts are composed of glandular, fatty, and fibrous tissue. They are attached to the overlying skin and to the muscles of the chest wall by suspensory ligaments.
2.8 Structures of the Breast
Each breast contains 15 to 20 divisions, called lobes, in which milk-secreting cells are located. Small tubular structures, the lactiferous ducts, extend from the milk-secreting cells, expanding slightly into lactiferous sinuses as they converge, in a spokelike fashion, toward the nipple, also called the mammary papilla. A pigmented area known as the areola surrounds the nipple.
2.9 Thyroid-Stimulating Hormone
Thyrotropin, or thyroid-stimulating hormone (TSH), is another substance secreted by the anterior pituitary lobe. It controls the release of thyroid hormone and stimulates the growth and function of the thyroid gland. The combining form thyr/o means thyroid, and you know that -tropin means stimulating.
2.11 Adrenocorticotropic Hormone
Adrenocorticotropic hormone (ACTH) is also called adrenocorticotropin. Again, the name of the hormone indicates its target tissue. The target tissue of ACTH is the outer portion of the adrenal gland, the adrenal cortex. The combining forms adren/o and adrenal/o mean pertaining to the adrenal gland and cortic/o refers to the cortex, the outer layer.
ACTH stimulates the growth of the adrenal cortex and causes it to secrete three steroid hormones, particularly cortisol.
2.12 Gonadotropins
The anterior pituitary secretes two gonadotropic hormones, that is, hormones that target the gonads or sex glands. The combining form gonad/o means pertaining to the gonads. The gonadotropic hormones, also called gonadotropins, are known as follicle-stimulating hormone and luteinizing hormone.
Follicle-stimulating hormone (FSH) stimulates the growth of the ova, or eggs, in the female and of sperm in the male.
Luteinizing hormone (LH) causes the secretion of sex hormones in both males and females. In women it causes production of estrogen and progesterone and stimulates the process of ovulation. In males LH stimulates production of testosterone. It is often referred to as interstitial cell-stimulating hormone (ICSH) because it spurs development of the interstitial cells of the testes.
Puberty is the period of life marked by the development of secondary sex characteristics and the attainment of the capability to sexually reproduce. The hypothalamus and the anterior pituitary hormones trigger the onset of puberty.
2.13 Melanocyte-Stimulating Hormone
Melanocyte-stimulating hormone (MSH) is also secreted by the anterior pituitary gland. MSH affects the skin's pigment-producing cells. When an excessive amount of MSH is secreted, pigmentation of the skin is increased.
You will recall from Module 16 that a melanocyte is a pigment cell, found principally in the skin; the combining form melan/o means black.
2.14 Threaded Case Study: Larry
Before we go on to look at the posterior lobe of the pituitary and its hormones, let's return to Larry who's visiting with the endocrinologist, Dr. Tyler. In addition to the fatigue he's been experiencing, Larry tells Dr. Tyler that he's noticed an increase in his appetite and in his sense of thirst. He also reports having to get up several times at night to use the bathroom. Dr. Tyler carefully reviews Larry's family's health history, conducts a thorough physical assessment, and orders a series of blood and urine tests.
2.15 Antidiuretic Hormone
The posterior lobe of the pituitary gland is stimulated by nerve impulses from the hypothalamus to release the hormones that are stored there. The two hormones secreted by the posterior pituitary gland are antidiuretic hormone (ADH) and oxytocin.
The term antidiuretic is created from anti-, meaning against, and diuretic, which means pertaining to diuresis, the production of urine. Antidiuretic hormone (ADH) decreases the production of urine by causing the kidney's tubules to reabsorb water and return it to the blood.
In addition, ADH, also called vasopressin, influences the smooth muscles of the blood vessels to contract; their constriction elevates blood pressure. You will recall that the combining form vas/o can indicate a relationship to blood vessels.
2.16 Oxytocin
Oxytocin, the second hormone secreted by the posterior pituitary in females, serves a very important function during the process of labor and delivery: It stimulates the smooth muscles of the uterus to contract.
Oxytocin is also responsible for the release, or "let-down," of milk from the mammary glands in response to an infant's suckling.
2.17 Pineal Gland
Also contained within the cranial cavity, along with the pituitary gland and the hypothalamus, is the pineal gland. The pineal gland is a cone-shaped structure whose functions are not all clearly understood.
The gland appears to receive information via a branch of the optic nerve about the amount of daylight and to respond by producing the hormone melatonin. Melatonin is believed to act on specific receptors that influence the body's biological clock by regulating the sleep/wake cycle.
3.1 Thyroid Gland
The thyroid gland, the largest endocrine gland, is located in the anterior neck. It surrounds the front and sides of the trachea just below the thyroid cartilage. The gland consists of right and left lobes, connected in the middle by a narrow strip of tissue called the isthmus. In medical terms, the thyroid gland is indicated by the combining forms thyr/o and thyroid/o.
3.2 Hormones Secreted by the Thyroid Gland
Cells in the thyroid gland secrete two hormones: triiodothyronine, or T3, and tetraiodothyronine, which is also called thyroxine or T4. Both of these thyroid hormones are synthesized from iodine, a chemical element that is a dietary nutrient found in seafood, salt, and some dairy products. The combining form iod/o means iodine.
Thyroid hormones tend to increase the metabolic rate, speeding up the processes by which food is converted into energy and by which the body uses fuel for its activities. These hormones are necessary for normal growth and development.
3.3 Thyroid Tissue
Thyroid tissue consists of tiny units, or follicles. The follicles are filled with a clear, thick substance known as colloid that contains several proteins and few cells.
Other cells within the thyroid gland secrete the hormone thyrocalcitonin (TCT), also called simply calcitonin. Thyrocalcitonin, which is not under the influence of the thyroid-releasing and thyroid-stimulating hormones, regulates the amount of calcium in the blood. Calcitonin induces calcium to leave the blood and enter bone tissue for increased bone formation. You will recall from previous modules that the combining form calc/i means calcium.
3.4 Parathyroid Glands
The parathyroid glands are tiny structures, usually four, attached to the posterior wall of the thyroid gland. They are indicated, in medical terms, by the combining form parathyroid/o. It is easy to remember the location of these glands because the prefix para- means near or beside and thyroid/o means thyroid.
These glands secrete parathyroid hormone (PTH), or parathormone. PTH acts on three target tissues—bone, kidneys, and the digestive tract—to increase the level of calcium in the blood. It stimulates the release of calcium from bone tissue, causes the kidneys to reabsorb calcium from the urine, and together with Vitamin D, it increases the absorption of calcium from the digestive tract.
As you can see, PTH has an effect on blood calcium levels that is opposite to that of calcitonin. Together these two hormones help to maintain the correct balance of calcium in the blood. This is accomplished by a mechanism called negative feedback, in which information about the effect of a hormone is supplied to the gland that secretes it. In this way, the amount of hormone delivered to the target tissue can be adjusted and its effect altered, if necessary.
3.5 Thymus Gland
The thymus gland lies in the mediastinum, beneath the sternum. You will recall from Module 8 that the thymus is an organ of the lymphatic system. However, it also has an endocrine function, the secretion of a hormone called thymosin. Thymosin stimulates the development of the immune system and the production of lymphocytes. The thymus is much larger in children than in adults.
3.7 Adrenal Glands
The adrenal glands, also called the suprarenals, are two small secretory organs, each of which sits atop a kidney. Medical terms containing the combining form adren/o refer to the adrenal glands.
Each gland consists of two regions: the outer portion, called the adrenal cortex, and an inner part, the adrenal medulla. The two regions of the adrenal glands secrete different hormones.
3.8 Outer Layer of Adrenal Cortex
The adrenal cortex secretes three types of steroid hormones that are known collectively as corticosteroids. The cortex consists of three distinct layers, each of which secretes a specific class of cortical hormones.
The outer layer, or zone, of the cortex produces the mineralocorticoids, the most important of which is aldosterone. Mineralocorticoids regulate the amount of mineral salts in the blood. Aldosterone, by targeting the kidney, increases the amount of sodium and decreases the amount of potassium in the blood.
3.9 Middle Layer of Adrenal Cortex
Cells in the middle layer of the adrenal cortex secrete the hormones known as glucocorticoids. These hormones help to maintain normal blood glucose levels and normal blood pressure. You will recognize the combining form gluc/o, meaning glucose.
Cortisol, the main glucocorticoid, is also known as hydrocortisone. Release of this hormone by the adrenal cortex occurs in response to the secretion of ACTH by the anterior pituitary, under the direction of the hypothalamus. Not only does cortisol promote the conversion of proteins and fatty acids to glucose, it also exerts an anti-inflammatory effect. Consequently, it is secreted in greater amounts during times of physiologic stress. Cortisol and cortisone, a similar glucocorticoid, can be prepared synthetically and are prescribed to treat inflammatory conditions.
3.10 Inner Layer of Adrenal Cortex
The inner layer of the adrenal cortex secretes small amounts of male and female sex hormones: androgens, estrogens, and progestins. These hormones, which are also secreted by the ovaries and testes, are responsible for the manifestation of secondary sex characteristics and are required for reproduction.
The combining form andr/o means male, and estr/o means female. You will recall that the suffix -gen means producing or forming. Thus, it is androgens that cause males to be masculine and estrogens that create female characteristics.
Progestin comes from pro-, meaning before, and gest/o, which refers to pregnancy. Thus, progestins are hormones that prepare the female body for pregnancy.
3.11 Adrenal Medulla
The adrenal medulla secretes two important nonsteroidal hormones that, because they contain a chemical group called a catechol, are known as catecholamines. The two hormones are epinephrine, also called adrenaline, and norepinephrine, also called noradrenaline.
These hormones exert effects similar to those of the sympathetic nervous system. They help the body respond to stress by elevating the blood pressure, increasing the heart rate, dilating the bronchial passages and increasing the respiratory rate, and making more glucose available to the cells.
3.13 Pancreas and Islets of Langerhans
The pancreas, indicated by the combining form pancreat/o, is a long gland that lies horizontally across the posterior wall of the upper abdomen. It is composed of both endocrine and exocrine tissue. As an exocrine gland, the pancreas produces pancreatic juices that aid in the digestion of food.
The islets of Langerhans are clusters of cells, scattered throughout the pancreas, that form the endocrine portion of the gland. The islets consist of two types of cells—alpha cells that secrete the hormone glucagon and beta cells that produce insulin. Both of these hormones help regulate blood glucose levels. You will recall that the combining form gluc/o means glucose. The suffix -agon means to gather or assemble. The combining form that means insulin is insulin/o.
3.14 Insulin
Insulin lowers blood glucose levels by transporting glucose from the blood into the cells and by stimulating the cells to burn glucose for energy. It also promotes the conversion of glucose to glycogen for storage in the liver. Both glyc/o and glycos/o mean sugar. Thus, glycogen means forming sugar and is a substance formed from sugar that can be converted back into sugar.
Glucagon antagonizes, or opposes, the effect of insulin. When blood sugar levels are low, glucagon stimulates the conversion of glycogen to glucose. It also triggers the transformation of fatty acids and amino acids into glucose.
3.15 Threaded Case Study: Larry
Dr. Tyler will use a variety of diagnostic tools to help her assess Larry's health problems. These will include tests that measure the amount of insulin in Larry's blood. We'll learn more about these tests later in this module.
3.16 Estrogens and Progestins
As we learned in Module 12, the ovaries are the primary female sex organs. They secrete two types of female sex hormones: estrogens and progestins. The estrogens, which include estradiol and estrone, are responsible for the expression of female sexual characteristics and for maintaining the proper sequence in the female reproductive cycle. Progesterone, the principal progestin, prepares the uterine lining for pregnancy and maintains it during pregnancy.
3.18 Testosterone
You'll remember from Module 12 that the testes, the primary male sex organs, are located in the scrotum and secrete the male sex hormone, testosterone. Testosterone is responsible for the maturation of secondary sex characteristics in the male.
The releasing hormones of the hypothalamus and the gonadotropins of the anterior pituitary control both the male and female hormones.
1.1 Gigantism
You will recall that the general term for pathology of any gland is adenopathy. Many endocrine system disorders involve either hypersecretion, excessive production, or hyposecretion, underproduction, of hormones.
We'll begin our study of endocrine pathology by examining abnormal conditions that arise in response to hypersecretion of the anterior lobe of the pituitary gland. Pituitary hypersecretion almost always involves growth hormone and may involve other pituitary hormones as well.
When hypersecretion of growth hormone, or hyperpituitarism, occurs before puberty, it results in gigantism, a condition characterized by excessive size and stature. This condition is indicated in medical terms by the combining form gigant/o.
1.2 Acromegaly
When hypersecretion occurs during adulthood, after the epiphyseal plates of the long bones have ossified, the condition that results is known as acromegaly. Acromegaly is a chronic metabolic disorder that involves the gradual enlargement of the bones of the face, jaw, and extremities. You will recall that the combining form acr/o means extremity and the suffix -megaly means enlargement.
Both gigantism and acromegaly are caused by adenomas of the pituitary. Did you recognize the word parts aden/o, meaning gland, and -oma, meaning tumor? Diagnosis of pituitary adenoma is aided by computed tomography (CT) scanning and magnetic resonance imaging (MRI). Treatment involves irradiation or excision of the neoplasm.
1.3 Pituitary Dwarfism
Hypopituitarism is the term for hyposecretion of one or more pituitary hormones. This may be a hereditary condition, or it may be caused by circulatory problems or tumor.
Hyposecretion of growth hormone produces pituitary dwarfism. With this condition, the body is properly proportioned, but growth is stunted and height typically does not exceed 4 feet.
Pituitary dwarfism is usually diagnosed during childhood with radiographic examination of the bones and tests such as radioimmunoassay (RIA), a laboratory measure that assesses hormone levels in plasma. Administering growth hormone treats the condition.
Pituitary hyposecretion due to atrophy of the gland causes ill health and physical wasting and is termed pituitary cachexia. Deficiencies of ACTH and TSH have powerful systemic effects and are life threatening when not successfully treated.
1.4 Diabetes Insipidus
Hyposecretion of antidiuretic hormone (ADH) results in a condition known as diabetes insipidus (DI). When ADH levels are insufficient, the target organ, the kidney, fails to reabsorb needed salts and water. This problem is evidenced by the excretion of large quantities of urine and by excessive thirst.
Perhaps you remember that poly- means multiple or excessive. The suffix -uria means urine or urination, and -dipsia means thirst. Thus, polyuria and polydipsia, respectively, indicate excessive urination and excessive thirst and are terms for the symptoms of diabetes.
Causes of DI include brain tumors, central nervous system infections and diseases, and closed head trauma. Depending on its etiology, DI may be treated by fluid replacement and the administration of ADH by either injection or inhalation.
1.5 Hypogonadism
Decreased pituitary secretion of the gonadotropins, FSH and LH, causes decreased function of the gonads and a decreased supply of the primary sex hormones usually produced by the ovaries and testes. This condition, called hypogonadism, causes retarded growth and sexual development.
2.1 Goiter
Abnormalities of the thyroid gland may involve hypersecretion, hyposecretion, enlargement, or inflammation. The general term for disease of the thyroid gland is thyropathy, and the term for thyroid inflammation is thyroiditis. Hyperthyroidism is the excessive secretion of the thyroid hormones, and hypothyroidism is a state of deficient thyroid gland activity.
Enlargement of the thyroid, which is known as goiter, may occur in conjunction with increased, decreased, or normal levels of hormone secretion. Endemic goiter occurs in certain geographic areas among populations that lack sufficient dietary iodine. The enlargement results from the collection of colloid, a jellylike substance, within the gland. Another kind of goiter, nodular or adenomatous goiter, may occur in the presence of hyperthyroidism.
2.2 Graves' Disease
The most common form of hyperthyroidism is Graves' disease. Although the origin of this disorder is unknown, its expression is believed to involve dysfunction of the immune system and to be influenced by both genetic and environmental factors. The signs of hyperthyroidism include tremor, nervousness, weight loss, fatigue, and palpitations. One of the most prominent features of advanced Graves' disease is exophthalmos, abnormal protrusion of the eyeballs, a condition caused by increased deposits of fat in the tissues at the back of the eye socket.
Thyrotoxicosis is the term for elevated levels of thyroid hormones in the blood. The most common cause of thyrotoxicosis is the overproduction of these hormones, as in Graves' disease, but this condition can result from thyroid inflammation that causes release of stored thyroid hormone without accelerated synthesis. It can also result from ingestion of exogenous thyroid hormone.
2.3 Testing for Graves' Disease
Graves' disease is diagnosed by thyroid function tests that include laboratory measurements of thyroid hormone levels in the blood.
Another test of thyroid function is the nuclear medicine procedure called a thyroid scan, or radioactive iodine uptake (RAIU). This test involves the administration of either radioactive iodine (131I) or isotope-tagged iodine and mapping its absorption in the thyroid gland using the gamma camera. A man-made radioisotope widely used for tagging other atoms is technetium (99mTc). Assessment of iodine uptake is diagnostic because absorption of iodine by the thyroid is increased in hyperthyroidism.
Exophthalmometry is a diagnostic method for measuring exophthalmos, the forward displacement of the eyes that occurs with advanced Graves' disease.
Treatment of hyperthyroidism may involve partial or total removal of the thyroid gland or administration of drugs to suppress thyroid hyperactivity.
2.4 Cretinism
Hypothyroidism—underactivity of the thyroid gland—has many possible causes. These include the surgical removal of the gland, decreased secretion of hormones that stimulate the thyroid, atrophy of the gland, and endemic goiter.
Cretinism is a congenital condition associated with severe hypothyroidism. Characteristics of this disorder include dwarfism and mental retardation. Early treatment with thyroid hormone may promote normal physical growth but may not reverse intellectual deficits.
2.5 Myxedema
Myxedema is another term for hypothyroidism. Inadequate secretion of thyroid hormone leads to a general slowing of all physical and mental processes. Metabolic activity of all cells of the body decreases, reducing oxygen consumption and decreasing both energy production and body heat. Fatigue and weight gain are typical. Changes in mood and personality simulating psychiatric illness may occur.
Myxedema coma is a severe, life-threatening condition that can occur when myxedema is allowed to progress untreated.
Myxedema can be successfully treated with administration of thyroid hormone.
2.6 Thyromas
Tumors of the thyroid gland, thyromas, may be benign or malignant. Cancerous thyroid neoplasms are rare and tend to grow more slowly than other types of malignancies. A hard, painless nodule in an enlarged thyroid characterizes these cancerous neoplasms.
Radioactive iodine uptake (thyroid scan) studies can help to establish the diagnosis of thyroid carcinoma.
Tumors of the thyroid are treated by surgical removal. Surgical incision into the thyroid gland is called thyroidotomy. This is not to be confused with thyroidectomy, which is excision, or removal, of the gland. Surgical removal of malignant tumors is usually followed by high-dose radioactive iodine therapy to destroy any remaining cancerous cells.
Take care to discriminate between the terms thyroma and thymoma; recall from Module 8 that a thymoma is a tumor of the thymus gland.
2.7 Hypercalcemia
Disorders of the parathyroid glands may also be categorized according to whether they involve hypersecretion or hyposecretion of parathyroid hormone (PTH).
Hyperparathyroidism, with its resulting high levels of circulating PTH, leads to an excessive amount of calcium in the blood, a condition called hypercalcemia.
2.8 Parathyroidectomy
Usually hyperparathyroidism is caused by an adenoma of one of the parathyroid glands. The illustration shows a parathyroidoma, which may be treated by excision of the tumor. Excision of the parathyroid gland is called a parathyroidectomy.
2.9 Hypocalcemia
Hypoparathyroidism describes the condition in which low levels of circulating PTH result in an inadequate amount of calcium in the blood, or hypocalcemia, sometimes referred to as calcipenia.
Signs of severe hypocalcemia include cardiac arrhythmias; numbness and tingling of the lips and fingertips; cramps; convulsions; twitching of the muscles; and sharp flexion of the wrist and ankle joints, as depicted in the illustration. Hypoparathyroidism is treated with administration of calcium and also of vitamin D, which facilitates the absorption of calcium.
3.1 Adrenopathy
You will recall from an earlier lesson in this module that the adrenal glands consist of two regions: the outer area, or cortex, and the inner region, the medulla. Each region secretes different hormones, and alterations in their levels result in a variety of disorders, known collectively as adrenopathy. Take care to discriminate between adrenopathy, a disorder of the adrenal glands, and adenopathy, a disorder of any gland.
To begin with, any inflammation of the adrenal gland is called adrenalitis, and an enlargement of one or both of the adrenal glands is referred to as adrenomegaly.
3.2 Potassium Imbalances
You'll recall from Section I of this module that the outer layer of the adrenal cortex produces aldosterone and that this hormone increases the amount of sodium and decreases the amount of potassium in the blood.
When excessive potassium is allowed into the bloodstream, the result is a condition called hyperkalemia. A deficient level of potassium in the blood is hypokalemia. A deficient level of sodium in the blood is called hyponatremia.
3.3 Adrenal Virilism
When tumors cause hypersecretion of androgens or estrogens before puberty, this is called adrenogenital syndrome. This can lead to early puberty and sex drive development in males.
Excess secretion of the androgens by the inner layer of the adrenal cortex in women leads to a condition called adrenal virilism. Virilism comes from the term virile, which means masculine. This disorder involves the expression of male secondary sexual characteristics including deepening of the voice and hirsutism. Hirsutism is the abnormal growth of hair, particularly male pattern hair growth, on females.
Conversely, when a tumor causes abnormal secretion of estrogens in males, the result is often gynecomastia, the development of breasts similar to those of a mature female.
Typically, the hypersecretion of androgens that results in adrenal virilism is caused by a tumor of the adrenal gland. The condition is managed by suppressing hormone overproduction with medication or by surgically removing the adrenal gland, a procedure known as adrenalectomy.
3.5 Cushing's Syndrome
The general term for increased secretion by the adrenal glands is hyperadrenalism.
Hypersecretion of cortisol from the adrenal cortex produces a complex of symptoms called Cushing's syndrome. Development of Cushing's syndrome may reflect the effect of excessive levels of adrenocorticotropic hormone (ACTH) on its target organ, the adrenal gland, or may be caused by a tumor of the adrenal cortex. The use of glucocorticoids to treat conditions such as arthritis and lupus also produces the symptoms of Cushing's syndrome.
The person with Cushing's syndrome will typically display obesity; a round, moonlike appearance of the face; and fatty deposits on the chest, abdomen, and upper back. Muscular atrophy, osteoporosis, and hypertension may also occur. Treatment of Cushing's syndrome involves reduction of the amount of cortisol secretion, either pharmacologically or surgically.
3.6 Addison's Disease
Abnormally decreased function of the adrenal cortex may result in the condition known as Addison's disease. In this disorder, which is potentially life threatening, all three categories of adrenal steroids—mineralocorticoids, glucocorticoids, and androgens—are deficient.
Addison's disease is believed to be an autoimmune disorder, a dysfunction of the immune system in which the individual produces antibodies that destroy adrenal tissue. Symptoms of the disorder include weakness, fatigue, and anorexia. Bronzed pigmentation of the skin and mucous membranes is also typical, caused by increased levels of MSH.
Treatment of Addison's disease includes replacement of adrenal hormones and management of the underlying cause of the illness.
3.7 Breast Disease
While there are many potential disorders of the breasts, the condition of greatest concern is a malignant tumor—breast cancer. The medical term for breast cancer is mastocarcinoma.
Here are some terms for other breast conditions:
mastitis: inflammation of the mammary gland(s), occurring most commonly during lactation
fibrocystic breast disease (see illustration): the presence of one or more benign cysts within the breast(s)
mastodynia: breast pain, often caused by fibrocystic disease and also a characteristic of mastitis
mastoptosis: prolapse or sagging of the breasts
3.8 Diagnosis of Breast Disease
Because early detection is a critical factor in successful treatment of breast cancer, monthly breast self-examination (BSE) is recommended for all women. This involves both observation and palpation of the breasts to detect any lumps or other changes that could indicate disease.
Mammography (shown in the illustration) is a special kind of radiographic imaging technique to detect and identify breast disease, both benign and malignant. Note the familiar word parts in this term: mamm/o, meaning breast, and –graphy, which means the making of an image or record. The American Cancer Society recommends annual mammography for all women over the age of 40 as a screening test for breast cancer. Technical advances in digital mammography have proven to be more diagnostically accurate than conventional radiographic techniques using film.
Diagnostic ultrasonography is also used in the diagnosis of breast disease. It is particularly helpful in discriminating between cystic tissue and neoplastic growth. There are specific applications for magnetic resonance imaging (MRI) in the diagnosis of breast disorders as well.
3.9 Treatment of Breast Conditions
The principal treatment for breast cancer is excision of the tumor either by surgically removing the entire breast, called mastectomy (Fig. A), or by removing the tumor and surrounding tissue from the breast, called lumpectomy (Fig. B). Radiation therapy and/or chemotherapy may be used in addition to surgery.
Treatment of fibrocystic disease consists primarily of dietary change and pharmacologic therapy, including dietary supplements and sometimes hormones. Wearing a support bra is helpful for some patients, as is the application of heat. Lumpectomy may be indicated for large, painful cysts.
The surgical fixation of sagging breasts is called mastopexy. Plastic surgery for the cosmetic repair, restoration, enlargement, or size reduction of the breasts is termed mammoplasty.
4.1 Threaded Case Study: Larry
We've been talking about endocrine problems in terms of either the hypersecretion or the hyposecretion of hormones. Larry's lab tests have revealed that his health complaints are related to hyposecretion of the hormone insulin. We'll catch up with him later when he returns to discuss these results with Dr. Tyler.
4.2 Hypoglycemia
Insulin, as you'll recall, is one of the two hormones secreted by the pancreas. Its function is to regulate the amount of glucose in the blood. An excessive amount of insulin lowers the blood glucose level, a condition known as hypoglycemia. Shakiness, sweating, headache, weakness, and loss of consciousness are among the symptoms associated with hypoglycemia.
Elevation in the amount of insulin, hyperinsulinism, may be caused by an insulin-secreting tumor in the pancreas, arising from the islets of Langerhans, or by exceeding a prescribed dose of the hormone. Administering glucose may reverse the symptoms of this condition, but the underlying problem must be identified and treated. Adjusting the diet or the prescribed dose of insulin may be all that is necessary. The usual diagnostic test for pancreatic tumor is a computed tomography (CT) scan with injection of an intravenous contrast medium.
4.3 Hyperglycemia
A deficiency of insulin in the blood allows for the accumulation of potentially life-threatening amounts of glucose. This condition is called hyperglycemia. With abnormally low levels of insulin, glucose is not properly transported to the cells nor is it adequately converted within the cells for use by the body as a source of energy. This insufficiency of insulin is called hypoinsulinism.
An inadequate supply of insulin from the pancreas may be caused by pancreatic cancer or by inflammation of the pancreas, called pancreatitis (as seen in the illustration). The most common cause, however, is diabetes mellitus (DM).
4.4 Type 1 Diabetes Mellitus
There are two major types of diabetes mellitus. Heredity plays an important role in both types of the disorder. In type 1, little or no insulin is produced because the beta cells of the islets of Langerhans that secrete the hormone have been decreased in number by an abnormal autoimmune process. This type of the disorder is also called insulin-dependent diabetes mellitus (IDDM) because insulin replacement is required for life to be sustained. Type 1 diabetes mellitus usually has its onset during childhood; for this reason, it is sometimes referred to as juvenile-onset diabetes.
|
|
|
4.5 Type 2 Diabetes Mellitus
Type 2 diabetes, which accounts for 90% of the cases of diabetes mellitus, is most frequently seen in adults 35 years of age and older. More than 70% of individuals that develop type 2 diabetes are obese.
In this form of the disorder, insulin production is variable; its levels may be decreased, normal, or elevated. Individuals affected by this condition are not insulin dependent; thus, type 2 diabetes is also referred to as non-insulin-dependent diabetes mellitus (NIDDM).
The disorder results from tissue unresponsiveness or resistance to insulin, which may be caused by hormone receptor defects or too few receptors on the surfaces of target cell membranes. As a consequence, the insulin that is produced is not effective.
4.6 Gestational Diabetes
A third type of diabetes, gestational diabetes, sometimes develops during pregnancy because of overall hormonal changes at that time. Typically, this condition resolves after childbirth, but in many cases, it recurs years later as type 2 diabetes.
4.7 Symptoms of Diabetes
High levels of glucose in the bloodstream draw water out of the cells; consequently, polyuria and polydipsia are hallmark characteristics of all types of diabetes.
Individuals with these disorders may also experience increased appetite and food intake because, with the unavailability of glucose, the cells seek energy by emitting chemical signals of hunger. You will recall from previous modules that the term for excessive hunger is polyphagia.
Excess glucose in the blood spills over (is excreted) into the urine; this condition is called glycosuria.
4.8 Diabetes Testing
After careful consideration of an individual's health history, a diagnosis of diabetes may be confirmed with a variety of laboratory tests. One such measurement is the fasting blood sugar (FBS) test, which assesses blood glucose levels after an 8- to 10-hour period of fasting.
Another laboratory examination is the glucose tolerance test, in which a measured amount of glucose is administered to a fasting patient and blood glucose levels are checked periodically over several hours.
A recently developed test, Hb AIC, is now sometimes used instead of the glucose tolerance test. This measurement of a specific hemoglobin, Hb AIC, provides an accurate indication of glucose control over a period of time, rather than on a single day. It is particularly useful in evaluating childhood diabetes and gestational diabetes.
4.9 Threaded Case Study: Larry
Larry's health history, his presenting complaints, and the results of the lab studies led Dr. Tyler to conclude that Larry has type 2 diabetes mellitus. In fact, Larry's family history revealed that his father and two of his siblings have NIDDM. Larry and Dr. Tyler will now discuss what will be involved in managing the disorder.
4.10 Complications of Diabetes Mellitus
Diabetes that is untreated or is inadequately controlled can give rise to a host of very serious complications.
Because the cells cannot burn glucose, they are forced to burn protein and fat instead. The burning of large quantities of fat produces strong acids known as ketoacids. Ketoacids are chemical relatives of ketones, also called ketone bodies, which are carbon-based organic molecules. The combining form that means ketone is ket/o. The term ketosis refers to the abnormally increased concentration of ketone bodies in body tissues and fluids that occurs when fatty acids are incompletely metabolized.
The buildup of these ketoacids further alters the body's metabolic balance and creates a condition called diabetic ketoacidosis. Signs of ketoacidosis include abdominal pain, nausea, vomiting, a fruity odor of the breath, and ketonuria, the presence of ketones in the urine. If left untreated, ketoacidosis can lead to coma and, ultimately, death.
4.11 Diabetic Gangrene
In addition to problems like ketoacidosis, the long-term effects of high levels of blood glucose, hyperglycemia, are numerous, affecting almost every area of the body. An accumulation of fatty materials in the blood vessels can lead to a variety of circulatory complications, ranging from atherosclerosis, heart attack, and stroke to impaired blood supply to the extremities; this last condition can lead to diabetic gangrene, tissue necrosis with infection (Fig. A).
The kidney disease called diabetic nephropathy is a common complication, as is the destruction of nerves in the extremities, a condition known as diabetic neuropathy. Finally, the blood vessels of the retina may be affected, a condition known as diabetic retinopathy (Fig. B), resulting in visual loss and blindness.
Diabetics are also more likely than non-diabetics to develop cataracts and glaucoma. Diabetic retinopathy, cataracts, and glaucoma are discussed in detail in Module 15. Diabetic complications of the urinary system are discussed in Module 11.
4.12 Treatment of Diabetes
Insulin, administered by injection or infusion pump, is the standard treatment to control blood glucose in cases of type 1 diabetes mellitus. But the treatment of diabetes involves more than just pharmacologic management; it typically requires a number of lifestyle changes. These include developing a dietary regimen that's nutritionally balanced. Weight reduction and exercise are also important components of the treatment program.
Type 2 diabetes mellitus is treated by lifestyle change and the administration of oral hypoglycemic agents, also called glucose lowering agents (GLA). These medications help to regulate blood glucose by stimulating the beta cells to produce more insulin and by increasing the sensitivity of target tissue receptors. In some cases, insulin administration is needed.
4.13 Threaded Case Study: Larry
Dr. Tyler has prescribed an oral hypoglycemic agent for control of Larry's diabetes; however, Larry may eventually be able to regulate his blood glucose with good nutritional management, maintenance of a healthy weight, and exercise. He will learn to monitor his blood glucose levels and must take special care to prevent the complications of diabetes.
2 comments:
Sciatica pain is a common, but painful symptom of some pregnancies. I would like to suggest the following article on coping with sciatica during pregnancy: http://www.spineuniverse.com/displayarticle.php/article4133.html
My name is Jennifer Murphy and i would like to show you my personal experience with Depo-Provera.
I am 41 years old. Have been on Depo for at least 10 years now. (started so long ago, can't remember) Pills had me lying in the floor crying. They had taken Norplant off the market, and the idea of glass under my skin spooked me. I'm now over 40, so weight gain can't all be blamed on Depo, but I know it's responsible for about 10 lbs worth. No periods in a decade. Can you top that??? No bleeding, no PMS, no cramps, no surprise pregnancies. Miracle drug, as far as I'm concerned. I am now level headed and not a jumpy bag of hormones every month. No mood swings. I refuse to take calcium, as I have had a kidney stone in the past, so going for a dexascan later this month. You MUST watch your bone density. Long term, depo can affect bone density and it's not 100% reversible. Posters here are fussing about doctors hiding the truth of side effects, but most of what's posted here is not listed as a side affect of Depo, so the doctors aren't going to mention them. Some of what's listed here sounds l
I have experienced some of these side effects-
Slight weight gain - 5-10 lbs. Extremeties swell with heat.
I hope this information will be useful to others,
Jennifer Murphy
Depo-Provera Prescription Medication
Post a Comment