The Reproductive System

The reproductive system makes life possible. An individual does not need the system to survive, but the human race does. Without the reproductive system, babies would not be born to grow into adults to give birth to more babies. The human cycle would end. All living things on the planet reproduce more of their own kind, and they do so in one of two ways. Some organisms reproduce by splitting in half or by growing buds that eventually turn into copies of the original organism. This method, in which a single organism reproduces itself, is called asexual reproduction. The reproductive method whereby a male and female of a particular species interact and exchange genetic material to create offspring is called sexual reproduction. Humans reproduce by this latter method.

DESIGN: PARTS OF THE REPRODUCTIVE SYSTEM

The male and female reproductive systems form the halves that come together to create new human life. Each system is composed of primary and accessory reproductive organs. In both, the primary sex organs are called gonads. These gonads produce reproductive or sex cells called gametes; they also secrete sex hormones. Despite their joint purpose to produce offspring, the two systems are quite different in structure and function.

The male reproductive system

The primary organs in the male reproductive system are the testes. Their main function is to produce male gametes or sperm, which fertilize ova or female eggs (they also produce the male hormone testosterone). The reproductive ducts—epididymis, ductus deferens, ejaculatory duct, and urethra—carry sperm from the testes to the exterior of the body. Accessory glands—seminal vesicles, prostate gland, and bulbourethral glands—produce secretions that combine with sperm to create semen. The male genitalia (external sex organs) are the scrotum and penis.

The Reproductive System: Words to Know

Acrosome (AK-ro-sohm):

Tip of the head of a sperm cell that contains enzymes to digest the membrane of an ovum.

Adenosine triphosphate (ah-DEN-o-seen try-FOS-fate):

High-energy molecule found in every cell in the body.

Amnion (AM-nee-on):

Fluid-filled sac that surrounds a developing embryo/fetus.

Areola (ah-REE-oh-lah):

Circular, darkened area surrounding the nipple of each breast.

Alveolar glands (al-VEE-o-lar GLANDZ):

Glands within the lobes of mammary glands that produce milk.

Bulbourethral glands (bull-bo-yoo-REE-thruhl GLANDZ):

Glands located underneath on either side of the prostate gland in males that secrete fluid that becomes part of semen.

Cervix (SIR-viks):

Lower necklike portion of the uterus leading into the vagina.

Chromosomes (kro-meh—somes):

Threadlike structures found in the nucleus of cells that carry the genetic material or genes that determine heredity.

Circumcision (sirnkum-SIZH-un):

Surgical removal of the prepuce or foreskin of the penis.

Clitoris (KLI-to-ris):

Small protruding mass of erectile tissue at the top of the labia minora.

Corpus luteum (KOR-pus LOU-tee-um):

Yellowish remains of a burst ovarian follicle that secretes progesterone.

Ductus deferens (DUK-tus DEF-e-renz):

Passageway that carries sperm from the epididymis to the ejaculatory duct.

Ejaculation (ee-jack-you-LAY-shun):

Sudden ejection of semen from the penis.

Ejaculatory duct (ee-JACK-yoo-la-tor-ee DUKT):

Duct formed by the union of the ductus deferens and the duct of the seminal vesicle.

Endometrium (en-doe-MEE-tree-um):

Inner layer of the uterus that provides nourishment for a developing embryo and fetus and that sloughs off during the regular menstrual cycle.

Epididymis (ep-i-DID-i-mis):

Portion of the male reproductive duct system in which sperm mature or fully develop.

Estrogens (ES-tro-jenz):

Female steroid hormones secreted by the ovaries that bring about the secondary sex characteristics and regulate the female reproductive cycle.

Fallopian tube (fah-LOH-pee-an TOOB):

Tube connecting an ovary to the uterus and through which an ovum is transported.

Fimbriae (FIM-bree-ee):

Fingerlike projections at the end of a fallopian tube that partially surround an ovary.

Flagellum (flah-JELL-um):

Long, whiplike tail that helps provide locomotion in certain cells, such as sperm cells.

Follicle-stimulating hormone (FAH-lik-uhl STIM-yoolay-ting HOR-mone):

Gonadotropic hormone produced by the anterior pituitary gland that stimulates the development of follicles in the ovaries of females and sperm in the testes of males.

Gamete (GAM-eat):

Female or male reproductive or sex cell (egg or sperm).

Genitalia (jen-i-TAY-lee-ah):

External organs of the reproductive system.

Gonad (GO-nad):

Sex organ in which reproductive cells develop.

Greater vestibular glands (GRAY-ter ves-TI-byoo-lar GLANDZ):

Pair of mucus-secreting glands that lubricate the lower portion of the vagina.

Hymen (HI-men):

Thin membrane partially covering the external opening of the vagina.

Hysterectomy (his-teh-REK-teh-mee):

Surgical removal of the uterus.

Labia majora (LAY-bee-ah ma-JOR-ah):

Outer skin folds of the vagina.

Labia minora (LAY-bee-ah my-NOR-ah):

Inner skin folds of the vagina.

Lactiferous ducts (lak-TIF-er-us):

Ducts that carry milk from the alveolar glands to the surface of the nipple of a breast.

Luteinizing hormone (loo-tee-in-EYE-zing):

Gonadotropic hormone secreted by the anterior pituitary that stimulates, in women, ovulation and the release of estrogens and progesterone by the ovaries and, in men, the secretion of testosterone by the testes.

Mammary glands (MAM-uh-ree GLANDZ):

Milk-producing glands in female breasts.

Menarche (meh-NAR-key):

Beginning of menstruation or the first menstrual period.

Menopause (MEN-ah-paws):

Period in a woman's life when menstrual activity ceases.

Menstruation (men-stroo-A-shun):

Also known as menses, periodic (monthly) discharge of blood, secretions, tissue, and mucus from the female uterus in the absence of pregnancy.

Mons pubis (MONZ PYU-bes):

Fatty, rounded area at the top of the vulva.

Myometrium (my-oh-MEE-tree-um):

Outer layer of the uterus composed of interwoven smooth muscle cells.

Oocyte (OH-oh-site):

Immature or developing egg cell.

Ova (O-va):

Female gametes or eggs (singular: ovum).

Ovarian follicles (o-VAR-ee-an FOL-i-kulz):

Structures within an ovary consisting of a developing egg surrounded by follicle cells.

Ovaries (O-var-eez):

Female gonads in which ova (eggs) are produced and that secrete estrogens and progesterone.

Ovulation (ov-yoo-LAY-shun):

Release of a mature ovum from an ovary.

Oxytocin (ahk-si-TOE-sin):

Hormone produced by the hypothalamus and stored in the posterior pituitary that stimulates contraction of the uterus during childbirth and secretion of milk during nursing.

Penis (PEE-nis):

Male organ of reproduction and urination.

Placenta (plah-SEN-tah):

Temporary organ that provides nutrients and oxygen to a developing fetus, carries away wastes, and produces hormones such as estrogens and progesterone.

Prepuce (PREE-pyus):

Also called foreskin, the fold of skin over the glans or tip of the penis.

Progesterone (pro-JESS-te-rone):

Female steroid hormone secreted by the ovaries that makes the uterus more ready to receive a fertilized ovum or egg.

Prolactin (pro-LAK-tin):

Gonadotropic hormone secreted by the anterior pituitary that stimulates the mammary glands to produce milk.

Prostate gland (PRAHS-tate GLAND):

Muscular gland in males that surrounds the first inch of the urethra and secretes a fluid that becomes part of semen.

Scrotum (SKROW-tum):

External sac enclosing the testes.

Semen (SEE-men):

Thick, whitish, somewhat sticky fluid composed of sperm and glandular secretions that is propelled out of a male's reproductive tract during ejaculation.

Seminal vesicles (SEM-i-nuhl VESS-i-kulls):

Glands in males located at the base of the bladder that secrete fluid that becomes part of semen.

Seminiferous tubules (sem-i-NIFF-er-us TOO-byoolz):

Tightly coiled tubes within the testes that produce sperm.

Sperm:

Mature male sex or reproductive cell.

Testes (TESS-teez):

Male gonads that produce sperm cells and secrete testosterone.

Testosterone (tess-TAHS-ter-ohn):

Hormone secreted by the testes that spurs the growth of the male reproductive organs and secondary sex characteristics.

Umbilical cord (um-BILL-i-kull KORD):

Structure that connects the embryo/fetus to the placenta.

Uterus (YOU-ter-us):

Also known as the womb, the hollow organ in females that receives, retains, and nourishes a fertilized ovum or egg.

Vagina (vuh-JIGH-nah):

Muscular tube in women that extends from the cervix of the uterus to the vaginal opening.

Vulva (VUL-vah):

Female external genital organs.

Zygote (ZIE-goat):

Fertilized ovum.

THE TESTES. The testes are two small, egg-shaped structures suspended in the scrotum, a loose sac of skin that hangs outside the pelvic cavity between the upper thighs. In a male fetus, the testes develop near the kidneys, then descend into the scrotum just before birth.

Each testis measures about 1.5 inches (3.8 centimeters) long and 1 inch (2.5 centimeters) wide. Internally, a testis is subdivided into many lobes. Each lobe contains one to four tightly coiled tubes, called seminiferous tubules, in which sperm is produced. Each tubule averages about 31.5 inches (80 centimeters) in length. The combined length of all the seminiferous tubules in a testis equals about 0.5 mile (0.8 kilometer).

Mature sperm cells are the smallest cells in the body. Each tadpolelike sperm cell consists of three regions: the head, middle piece, and flagellum. The helmetlike head contains the male genetic material essential for reproduction. On the tip of the head is the acrosome, which contains enzymes to break down the membrane of an ovum so fertilization can occur. The middle piece contains a supply of adenosine triphosphate (ATP), a high-energy molecule found in every cell in the body. The sperm cell uses the ATP to power its flagellum, the long whiplike tail, to move the cell along.

Sperm from the seminiferous tubules are carried along by fluids through a network of tubes before entering the epididymis, the first of the male reproductive ducts.

THE EPIDIDYMIS. The epididymis is a tube about 20 feet (6 meters) in length. Tightly coiled on the posterior or back side of each testis, each epididymis takes up very little room. As sperm cells move through this tube, they absorb nutrients and become mature or fully developed, a process that takes about two weeks. The walls of the epididymis are made of smooth muscle cells, which helps propel sperms cells into the ductus deferens.

THE DUCTUS DEFERENS. The ductus deferens, also called the vas deferens, extends from each epididymis upward over the top of the bladder, then down its back side. The paired ducts measure between 16 and 18 inches (40 and 45 centimeters) in length. Their smooth muscular walls move the sperm along through peristaltic contractions, or a series of wavelike muscular contractions that move material in one direction through a hollow organ.

THE EJACULATORY DUCT. The ejaculatory duct is a short passageway that is formed by the union of a ductus deferens and the duct of a seminal vesicle. Each ejaculatory duct measures just under 1 inch (2.5 centimeters) in length. Both ejaculatory ducts empty sperm (from the ductus deferens) and fluid (from the seminal vesicle) into the single urethra.

THE URETHRA. The urethra extends from the base of the urinary bladder to the tip of the penis, a distance of 6 to 8 inches (15 to 20 centimeters). In males, the urethra serves both the reproductive and urinary systems. It transports sperm (with its fluid) and urine to the body exterior, but never both at the same time. When sperm enters the urethra from the ejaculatory ducts, a sphincter or ring of muscle at the junction of the bladder and urethra closes, keeping urine in the bladder (and also preventing sperm from entering the bladder).

ACCESSORY GLANDS AND SEMEN. The three accessory glands produce secretions that combine with sperm to create a whitish, somewhat sticky mixture called semen. Those secretions (the fluid part of semen) are known collectively as seminal fluid. Ejaculation is the sudden ejection of semen from the penis. A typical ejaculation releases between 0.07 and 0.17 ounce (2 and 5 milliliters) of semen. Although as many as 400 to 600 million sperm are contained in a typical ejaculation, they make up only about 1 percent of the volume of the semen because of their extremely small size.

The seminal vesicles are the first accessory glands to add secretions to sperm. Located at the base of the bladder, their ducts join with the paired ductus deferens to form the ejaculatory ducts. Their thick, yellowish secretion, which makes up about 60 percent of the seminal fluid, contains high amounts of fructose (sugar), vitamin C, and other substances. The secretion helps nourish and activate the sperm as its passes through the reproductive tract.

The prostate gland is a single, rounded gland that has a diameter of about 1.6 inches (4 centimeters). It surrounds the urethra as the urethra leaves the bladder. It produces an acidic, milky secretion that enters the urethra through several small ducts. This secretion makes up about 30 percent of the seminal fluid.

The bulbourethral glands are the last glands to add secretions to the seminal fluid. The tiny, pea-shaped glands are located underneath on either side of the prostate gland. Their secretion—a thick, clear mucus—enters the urethra when a man becomes sexually aroused before the secretions of the other accessory glands. The secretion coats the lining of the urethra and cleanses it of any traces of acidic urine that might be present. It also serves as a lubricant during sexual intercourse.

The secretion of all three accessory glands are slightly alkaline or basic (solutions containing a high number of hydrogen ions are acidic, those with a low number are alkaline or basic). This is important because the bacteria present in the female vagina create an acidic environment there. The alkaline seminal fluid neutralizes the acid in the vagina, allowing sperm in the semen to exist and move in the vagina so fertilization may take place.

MALE GENITALIA. The scrotum and penis are the male genitalia that hang outside the body. As stated earlier, the scrotum is a loose sac of skin that hangs outside the pelvic cavity between the upper thighs. It is divided into two compartments, each holding a testis. The scrotum holds the testes away from the body since normal body temperature is too warm for sperm to be produced. The temperature inside the scrotum is a few degrees cooler than inside the rest of the body. If the external temperature becomes very cold, muscles in the scrotum pull the testes closer to the body, maintaining the proper temperature for sperm production.

The penis is a tubular organ that surrounds the latter part of the urethra. It serves two purposes: to conduct urine outside the body and to deliver semen into the female reproductive tract. The two main parts of the penis are the glans (enlarged tip) and shaft (body). A fold of skin called the prepuce or foreskin covers the glans. It is common practice in certain cultures and religions to remove the foreskin surgically soon after birth, a procedure called a circumcision. The shaft contains three masses or columns of erectile tissue. Normally, this spongy tissue is not filled with much blood. During sexual arousal, however, blood flow to the tissue increases. The penis, engorged with blood, becomes longer, wider, and rigid. This event, called an erection, allows the penis to enter the female vagina and deliver semen to the female's reproductive tract.

The female reproductive system

The reproductive system in females is more complex than that in males. The system produces female gametes, called ova or eggs, and provides a protective space for an ovum to be fertilized and to develop until birth. The primary organs in this system are the ovaries. The accessory organs include the fallopian tubes, the uterus, the vagina, the genitalia, and the mammary glands.

THE OVARIES. The ovaries are two almond-shaped structures measuring about 1.5 inches (3.8 centimeters) in length. They are located on each side of the pelvis, one at the end of each fallopian tube. Ligaments attach the

ovaries to the walls of the pelvis and to the uterus (these latter ligaments are called ovarian ligaments).

Within each ovary are many tiny saclike structures called ovarian follicles. An ovary contains several hundred thousand of these follicles, which are present from birth. Each follicle consists of an immature or developing egg called an oocyte surrounded by one or more layers of cells called follicle cells. During a woman's life, however, only about 360 to 480 ovarian follicles will produce mature eggs or ova.

FALLOPIAN TUBES. The fallopian tubes, also called uterine tubes, connect the ovaries to the uterus. Each fallopian tube is about 4 inches (10 centimeters) in length and extremely narrow. The end of the tube that attaches

to an ovary has fingerlike projections called fimbriae that partially surround the ovary. The inner surfaces of the tubes are carpeted with cilia, microscopic hairlike structures projecting in from the inner lining.

THE UTERUS. The uterus, or womb, is a hollow, muscular chamber shaped like an upside-down pear. An average uterus measures about 3 inches (7.6 centimeters) in length and 2 inches (5 centimeters) in width. It weighs approximately between 1 and 1.4 ounces (30 and 40 grams). The uterus lies in the pelvis between the urinary bladder and rectum and is anchored in place by various ligaments.

The part of the uterus above where the fallopian tubes attach is called the fundus. The body is the large central portion. The narrow, lower end that projects a short distance and opens into the vagina is called the cervix.

The thick wall of the uterus is composed of two main layers: the myometrium and the endometrium. The myometrium, the outer layer, is made of smooth muscle cells (among the strongest in the body) that are interwoven to allow the uterus to expand to accommodate a growing fetus and to contract to force the fetus out at the end of pregnancy. The endometrium, the inner layer, provides a site for a fertilized egg to attach to receive nourishment during its development. If an egg is not fertilized, the endometrium sloughs off or is shed during the regular menstrual cycle.

THE VAGINA. The vagina is a muscular tube extending from the uterus to the genitalia. It lies parallel to the rectum. The vagina serves as a exit for menstrual fluids, receives the penis during intercourse, and forms the birth canal through which the fetus passes at the end of pregnancy. Normally, it measures about 4 inches (10 centimeters) in length, but to accommodate all of its activities, its length and width vary widely.

The external opening of the vagina (vaginal opening) is usually partially covered by a thin membrane called the hymen. This membrane is usually ruptured or broken during a women's first sexual intercourse, by the use of tampons during the menstrual period, or during a sports activity.

Bacteria normally exist in the vagina, living on nutrients found in the mucus secreted by the cervix. They are quite beneficial. Through their activities, they create an acidic environment in the vagina that inhibits or prevents the growth of pathogens (disease-causing organisms).

FEMALE GENITALIA. In females, the external sex organs are collectively called the vulva. The parts making up the vulva include the mons pubis, labia majora and minora, clitoris, and greater vestibular glands.

The mons pubis is the prominent fatty bulge at the top of the vulva. Beginning at puberty, this area is covered with pubic hair. Running down from the mons pubis are two hair-covered skin folds or flaps called the labia majora. They enclose two delicate, hair-free skin folds called the labia minora. The area within the labia minora, referred to as the vestibule, contains the openings of the urethra (through which urine passes) and the vagina.

At the top of the labia minora (above the urethral opening) lies the clitoris. A small protruding mass of erectile tissue, it is similar to the male penis. During sexual arousal or excitement, the sensitive clitoris becomes engorged with blood. Located in the floor of the vestibule on either side of the vaginal opening are a pair of glands called the greater vestibular glands. During sexual arousal, these glands secrete a mucus that lubricates the lower portion of the vagina.

MAMMARY GLANDS. Mammary glands are found in the breasts of both women and men. However, they normally function only in women. Mammary glands are modified sweat glands that are actually part of the integumentary system (skin). Although not directly involved in the reproduction process, mammary glands play an important role in providing nourishment for a newborn baby and their activities are controlled by hormones of the reproductive system. For these reasons, they are considered accessory reproductive organs.

On the outside of each breast, slightly below center, is a darkened, reddish brown area called the areola. In the center of the areola is a small protruding nipple.

Within each mammary gland are 15 to 25 lobes radiating inward from the nipple. The lobes are separated by connective tissue and fat. Within each lobe are chambers containing alveolar glands, which produce milk after a woman has given birth. Lactiferous ducts carry milk from the alveolar glands to small openings on the surface of each nipple. The milk is a mixture of water, proteins, fats, sugars, salts, and enzymes that have immune properties.

When a baby suckles a mother's nipple, nerve impulses are sent to the mother's hypothalamus. It then signals the posterior portion of the pituitary gland to secrete the hormone oxytocin. The hormone stimulates the contraction of the muscle cells around the lactiferous ducts, causing the ejection of milk through the nipple.

WORKINGS: HOW THE REPRODUCTIVE SYSTEM FUNCTIONS

The main functions of the male reproductive system are to produce sperm and to introduce that sperm into the female reproductive tract. The main functions of the female reproductive system are to produce ova, receive sperm from the male penis, house and provide nutrients to the developing embryo and fetus, give birth, and produce milk to feed offspring.

The activities of both reproductive systems are controlled by hormones (chemicals produced by the body that affect various bodily processes) released from the pituitary gland, which is located at the base of the brain behind the nose, and from the gonads in each system.

Hormones and the male reproductive system: Sperm production

In males, the testes produce male sex hormones called androgens (from the Greek word andros, meaning "man"). Testosterone is the most important of these. It spurs the growth of the male reproductive organs and the production of sperm. In addition, testosterone brings about the male secondary sex characteristics: deepening of the voice; appearance of hair under the arms, on the face, and in the genital area; and increased growth of muscles and heavy bones.

Testosterone is produced in the male fetus to stimulate the formation of the male duct system and accessory organs. Its production then declines and does not increase until puberty.

At puberty (usually occurring between the ages of twelve and sixteen in boys), the anterior portion of the pituitary gland releases luteinizing hormone. This hormone activates the cells surrounding the seminiferous tubules in each testis to begin secreting testosterone. The anterior pituitary then releases follicle-stimulating hormone, which stimulates the cells of the seminiferous tubules to begin producing sperm. In the presence of testosterone, the sperm are able to mature.

This process, begun at puberty, continues throughout a man's life. Millions of sperm are formed each day in the testes. Although this number decreases as a man ages, the production of sperm never completely stops.

Hormones and the female reproductive system: The menstrual cycle

In women, the ovaries secrete two groups of steroid hormones, estrogens and progesterone. Estrogens spur the development of the female secondary sex characteristics: enlargement of the breasts, appearance of hair under the arms and in the genital area, and the accumulation of fat in the hips and thighs. Estrogens also act with progesterone to stimulate the growth of the lining of the uterus, preparing it to receive a fertilized egg.

The ovaries do not begin to function until puberty (usually occurring between the ages of eleven and fourteen in girls). At this time, the anterior pituitary gland secretes follicle-stimulating hormone (FSH). This hormone stimulates a small number of ovarian follicles in an ovary to grow and mature. It also stimulates the follicle cells in those follicles to secrete estrogens. Together, FSH and estrogens help the oocyte (immature ovum) in each stimulated follicle to mature.

About fourteen days after the anterior pituitary secreted FSH, only one follicle in the ovary has developed to maturity with a mature ovum inside. The anterior pituitary then releases luteinizing hormone (LH), which causes the mature follicle to burst open and release its ovum through the ovary wall. This event is known as ovulation.

DEVELOPING "THE PILL"

Reproductive biologist Min-Chueh Chang (1908–1991) is best known for developing an oral contraceptive—commonly known as the birth control pill—in collaboration with American endocrinologist Gregory Goodwin Pincus (1903–1967) and American gynecologist and obstetrician John Rock (1890–1984).

In the early 1950s, Chang and Pinkus began to study the female hormone progesterone, believing it could provide them with clues about how to create an oral contraceptive (a substance that prevents conception). Through their research the scientists soon realized that increasing blood levels of progesterone could stop ovulation. They experimented with more than two hundred substances in order to find natural compounds that imitated the combined actions of progesterone and another female hormone, estrogen. At that point, they began a collaboration with John Rock of the Rock Reproduction Clinic in Brookline, Massachusetts. The team developed a pill made of three compounds, including estrogen and progesterone derived from a wild Mexican yam. They began testing their pill on human subjects, using groups of women in Brookline, as well as in Haiti and Puerto Rico.

Their trials were successful in stopping ovulation, but the researchers decided to slightly alter the pill they had developed. They wanted to try to eliminate estrogen from the pill because they considered it to be unnecessary. They thought that progesterone was the key ingredient they needed. Trials of this no-estrogen pill, however, had seriously negative results, including pregnancies and breakthrough bleeding (bleeding between menstrual periods) in the women they tested. The scientists restored estrogen to the pill, creating a form of contraception that was over 99 percent effective and relatively safe. The combined estrogen-progesterone pill was approved by the U.S. Food and Drug Administration in 1960.

The cilia carpeting the inner surfaces of the fallopian tubes wave back and forth, creating a current in the fluid that fills the tubes and spaces around the ovaries. The mature ovum that is released is drawn by these currents into the fallopian tube attached to the ovary. Muscle contractions in the walls of the tube also help propel the ovum along.

While the ovum is in a fallopian tube, the ovarian follicle that burst undergoes another transformation. LH, which triggered ovulation, also causes the ruptured follicle to change into another structure. This small yellow structure is known as the corpus luteum. It begins secreting another hormone, progesterone. The new hormone prevents the other stimulated follicles with their eggs from reachig full maturity. In combination with estrogens, it also causes the endometrium (lining of the uterus) to grow in size and secrete nutrients into the cavity of the uterus (to help nourish a developing embryo, if one is present). As the endometrium grows, so does its supply of blood vessels.

The mature ovum in the fallopian tube can only survive for twelve to twenty-four hours. Fertilization of the ovum by male sperm must occur within the fallopian tube within that time. If fertilization does not occur, the ovum enters the uterus and begins to break down. Blood levels of LH and FSH decrease dramatically. The corpus luteum continues to secrete progesterone for about ten to twelve days after ovulation. It then stops and begins to degenerate or shrivel up.

Without the presence of progesterone, the thickened endometrium begins to detach from the uterus and break apart. After a while, the tissue pieces of the endometrium (along with the blood vessels that nourished it) are discharged from the body in a flow of blood through the vaginal opening. This event is referred to menstruation or menses. The flow of blood, which is commonly called a period, usually lasts four or five days. The average amount of blood lost during a period ranges from 1.7 to 5 ounces (50 to 150 milliliters). Once menstruation ends, the endometrium begins to regenerate.

The beginning of menstruation marks the end of what is known as the menstrual cycle. The cycle begins with the secretion of FSH spurring ovarian follicles to mature. The time period of a menstrual cycle is normally about twenty-eight days (the length can vary from nineteen to thirty-seven days). As menstruation is occurring, new follicles in the other ovary are being stimulated by FSH and a new menstrual cycle is underway.

The first menstruation or menstrual period a girl undergoes at puberty is known as menarche. Menstrual cycles continue one after the other (unless a woman becomes pregnant) from puberty until a woman reaches her forties or fifties. At that time, the number of ovarian follicles in the ovaries has been exhausted and the ovaries no longer respond to FSH. Ovulation and menstruation cease, and blood levels of estrogens and progesterone decline. A decline in estrogen levels leads to a reduction in the size of the uterus and breasts. The walls of the vagina and uterus also become thinner. This change in a woman's reproductive system and organs is known as menopause.

Fertilization

The only time a woman does not experience a menstrual cycle between puberty and menopause is when she is pregnant (certain illnesses, emotional stress, and extensive physical activity can also stop menstrual cycles from occurring). For pregnancy to occur under normal conditions, an ovum must be fertilized by a sperm in a fallopian tube.

When a man ejaculates semen into a woman's vagina, the millions of sperm swim through the watery fluid inside the vagina and uterus. Of the multitude of sperm, only a relative few will reach an ovum in a fallopian tube, if one is present. A vast majority of sperm will be destroyed by white blood cells in the walls of the vagina and uterus. Of those that survive, many may not be able to swim to the top of the uterus. Of those that are able, half then swim into the wrong fallopian tube.

BIRTH CONTROL METHODS

Birth control or contraception is the deliberate effort to keep a woman from becoming pregnant. Attempts to prevent pregnancy date back to ancient times and cultures. Some form of contraception is currently used by more than half the women in the United States. Although widespread, contraception remains controversial, with some religious and political groups opposed to the distribution of contraceptives.

There are a number of contraceptive devices to prevent pregnancy, some more effective than others. The following are a few common devices:

Birth control pills: The most popular contraceptive in the United States. The pills contain hormones that are released into a woman's system on a regular basis to prevent pregnancy, either by inhibiting ovulation, preventing implantation of a fertilized egg, or by thickening the secretions throughout a woman's reproductive system so that her partner's sperm has less of a chance to meet her egg.

Condom: A sheath used to cover the penis to prevent semen from entering a woman's reproductive tract. Modern condoms are made of latex (rubber). Also used as an effective barrier against sexually transmitted diseases.

Contraceptive sponge: Device used to cover the cervix to prevent the passage of semen into the uterus. Was taken off the market in the United States in the early 1990s because of potential health risks, but has recently begun to be reintroduced.

Diaphragm: Rubber, cap-shaped device that fits over the cervix and prevents the passage of semen into the uterus.

IUD: Intrauterine device, a small plastic device placed inside the uterus of a women by a physician that prevents an embryo from developing in the wall of the uterus.

A permanent form of birth control—sterilization—can be achieved through surgical procedures. Men can undergo an operation called a vasectomy, in which both vas deferens are cut and tied so that sperm cannot be ejaculated. Women can undergo an operation called a tubal ligation, in which the fallopian tubes are either cut or tied so that an egg cannot pass down into the uterus.

Probably the most common contraceptive method in the world is coitus interruptus, in which a man withdraws his penis from a woman's vagina before ejaculating. Unfortunately, this practice has resulted in numerous accidental pregnancies. The rhythm method (in which intercourse is avoided on the days of the month when a woman is most likely to become pregnant) was and remains the only form of birth control approved by the Roman Catholic Church. Abstinence, or the complete avoidance of sexual activity, remains the most effective way to prevent pregnancy.

About 100 sperm eventually reach an ovum in a fallopian tube. They then attached themselves to the ovum's outer membrane. Enzymes in the acrosomes of the sperms begin to break down the membrane. Eventually, one sperm makes it through to the interior of the ovum. After it does, electrical changes occur in the membrane of the ovum that prevent the other sperm from entering.

The sperm and ovum each carry the genetic material that is necessary to generate and maintain human life. The threadlike structures that carry that genetic material (or genes) are called chromosomes. While all other body cells contain 46 chromosomes (23 pair), a sperm and an ova each contain only 23 single chromosomes. When the genetic material of a sperm combines with that of an ovum, fertilization or conception occurs. The fertilized egg, called a zygote, contains the normal human number of 46 chromosomes.

The zygote then travels down the fallopian tube and enters the uterus. By the time it has reached the uterus, the zygote (now called an embryo) is

a tiny ball of cells that are continually growing and dividing. About a week after fertilization, the embryo becomes embedded in the endometrium. Cells of the embryo then release a hormone that prevents the corpus luteum from degenerating. Estrogens and progesterone continue to be secreted and the endometrium remains intact. Menstruation does not occur and the menstrual cycle is stopped.

Other cells from the embryo combine with tissues from the uterus to form a temporary organ called the placenta. The placenta serves as the site where oxygen and nutrients pass from a woman to the embryo and where

STEPTOE AND THE FIRST TEST TUBE BABY

English gynecologist Patrick Steptoe (1913–1988) is best known for helping develop the technique of in vitro fertilization, a process by which an egg is fertilized by sperm outside of the body. Steptoe and his colleague, English physiologist Robert G. Edwards, received international recognition (both positive and negative) when their work led to the birth of the first so-called test tube baby in 1978.

In 1966, while working on fertility problems (the inability of a woman and man to conceive a child), Steptoe teamed up with Edwards. Using ovaries that had been removed for medical reasons, Edwards had previously pioneered the fertilization of eggs outside of the body, a procedure called in vitro fertilization. In this operation, a mature egg is removed from the female ovary and is fertilized with sperm in a petri (glass) dish. After a short incubation or development period, the fertilized egg is implanted in the uterus, where it develops as in a typical pregnancy. This procedure gives hope to women who cannot become pregnant because their fallopian tubes are damaged or missing.

For a decade, Steptoe and Edwards pursued their research, but met with little success. In addition, as news of their work began to spread, Steptoe and Edwards faced intense criticism. Scientists and religious leaders raised ethical and moral questions about tampering with the creation of human life. Members of British Parliament demanded an investigation, and the scientists' research funds were cut off. Nevertheless, Steptoe and Edwards continued their work.

Finally, in 1976, Steptoe met Leslie Brown, a thirty-year-old woman who had experienced problems with her fallopian tubes and could not conceive a child. Steptoe removed a mature egg from her ovary, and Edwards fertilized the egg in a petri dish using the sperm of her husband, Gilbert. After two days, Steptoe implanted the fertilized egg in Brown's uterus, where it continued to thrive as a normal pregnancy. On July 25, 1978, Brown gave birth to Joy Louise, a healthy 5.75 pound (2.61 kilogram) baby girl, the first human conceived outside of a woman's body.

wastes are taken away from the embryo. The placenta also produces hormones—estrogens, progesterone, and others—that help maintain pregnancy.

A fluid-filled sac, the amnion or amniotic sac, develops around the embryo. In this sac, the embryo will continue to develop, connected to the placenta by a blood vessel-containing tube called the umbilical cord. Nine weeks after fertilization, the developing embryo is referred to as a fetus. Approximately 270 days after fertilization, the fetus is ready to be born.

AILMENTS: WHAT CAN GO WRONG WITH THE REPRODUCTIVE SYSTEM

Many ailments and disorders can affect the male and female reproductive systems, preventing them from functioning properly. These conditions can range from mild to moderate to severe. Some are life-threatening.

THE DEVELOPMENT OF A HUMAN FETUS

An embryo is an organism in its earliest stages of development, produced when an ovum is fertilized by a sperm. Shortly after fertilization, the ovum begins to grow and develop. It divides to form two cells, then four, then eight, and so on. The cells then combined to form structures and systems. A developing human individual is considered an embryo from the time of fertilization until the ninth week of pregnancy. At that point, it is considered a fetus.

The following is a list of changes or appearances that mark each month in the development of a fetus:

Month 3: Head is abnormally large in proportion of the body. Facial features are present in crude form. Bone development increases. Brain continues to enlarge. Sex can be readily determined from the genitals. Approximate overall size: 3 inches (7.6 centimeters).

Month 4: Head still quite large, but arms and legs lengthen. Hair appears on head. Face begins to look more human. Eyes, ears, nose, and mouth are well-formed. Body systems continue to develop. Approximate overall size: 5 to 7 inches (13 to 18 centimeters).

Month 5: Body begins to grow more rapidly than head. Body is covered with silklike hair (lanugo). Skin is covered with a grayish-white, cheese-like coating (vernix). Skeletal muscles become active. Approximate overall size: 10 to 12 inches (25 to 30 centimeters).

Month 6: Eyelashes and eyebrows form. Eyelids begin to open. Lanugo has largely disappeared. Skin is wrinkled and red. Approximate overall size: 12 to 14 inches (30 to 35 centimeters).

Month 7: Body and head approach normal proportions. Weight increases substantially. Fat deposits are laid out beneath the skin, which becomes less wrinkled. Fingernails and toenails are present. In males, testes descend into the scrotum. Approximate overall size: 14 to 17 inches (35 to 43 centimeters).

Month 8: More fat is deposited under the skin. Most body systems are fully functional. Approximate overall size: 18 inches (46 centimeters).

Month 9: Skin appears whitish pink. Nails are fully developed. Lungs are more mature. Lanugo is shed. Fetus ready to be born. Approximate overall size: 19 to 21 inches (48 to 53 centimeters).

Vaginal yeast infections, caused by a species of yeast found in virtually all normal people, are common infections in women. While not serious, they can be uncomfortable and irritating until treated. Impotence, a condition in which a man is unable to maintain an erection, may be due to some physical or psychological problem. Again, this disorder does not threaten life, but it is a cause of concern to a man (and to his spouse or partner) as it prevents him from engaging in sexual intercourse.

The organs of the male and female reproductive systems are often sites where tumors or other growths develop. Many of these growths are cancerous. The following are some of the more serious diseases and disorders that can afflict the reproductive systems in males and females.

Breast cancer

Breast cancer develops when cells of the breast become abnormal and grow uncontrollably, forming tumors. The cancer cells can invade and destroy surrounding tissue, then spread throughout the body by way of the blood or lymph vessels. Every woman is at risk for breast cancer. Regardless of family history, a woman's risk for developing this type of cancer increases as she ages. In fact, 80 percent of all breast cancers are found in women over the age of fifty.

A woman's chance for developing breast cancer increases if her mother or sister have had breast cancer, if she has gone through menopause late in life, if she did not breastfeed her children, or if she did not have children or had them late in life. However, more than 70 percent of women who get breast cancer have none of these risk factors.

The following are all indications of possible breast cancer: a lump in the breast, changes in the nipple of the breast, dimpled or reddened skin over the breast, and change in size or shape of the breast.

More than 90 percent of all breast cancers are detected by mammography (a low-dose X ray of the breast). The American Cancer Society recommends that women between the ages of forty and forty-nine have a mammogram done every year or two; women aged fifty or over should have one every year.

AVERAGE GESTATION PERIOD OF DIFFERENT ANIMALS

Treatment options for breast cancer include surgery, chemotherapy, and radiation. During surgery, surgeons may remove only a portion of a woman's breast, her entire breast and some underarm lymph nodes, or her entire breast along with all of the underarm lymph nodes and chest muscles. The extent of the surgery depends on the type of breast cancer, whether the disease has spread, and the woman's age and health. After the cancer has been removed, the physician may recommend the woman undergo chemotherapy (using a combination of drugs to kill any remaining cancer cells and shrink any tumors) or radiation therapy (using X rays or other high-energy rays to kill any remaining cancer cells and shrink any tumors) or a combination of both.

Breast cancer cannot be prevented, but it can be treated successfully if diagnosed from a mammogram at an early stage.

Endometriosis

Endometriosis is a condition in which bits of tissue similar to the endometrium (lining of the uterus) grow in other parts of the body. Like the endometrium, this tissue builds up and sheds in response to monthly hormonal cycles. However, the blood discarded from these tissue implants has no natural outlet. It falls onto surrounding organs, causing swelling and inflammation. Eventually, scar tissue and adhesions develop in these areas.

The exact cause of endometriosis is unknown and there is no way to prevent the disease. It most commonly strikes women who are between the ages of twenty-five and forty. About 7 percent of the women in this age group in the United States are affected by the disorder.

The most common symptoms of endometriosis include menstrual pain beginning a day or two before the true menstrual period starts, abnormal bleeding during menstrual periods, and pain during sexual intercourse.

If endometriosis is discovered, treatment depends on a woman's symptoms, her age, and the extent of the disease. For mild cramping and menstrual pain, over-the-counter pain relievers are taken. Medications similar to hormones may be given to reduce pain and shrink or stop the spread or growth of the condition. The only permanent method to eliminate endometriosis is the surgical removal of the uterus, ovaries, and fallopian tubes. For women with minimal endometriosis, laser surgery to remove the endometrial tissue implants and ovarian cysts may be employed.

REPRODUCTIVE SYSTEM DISORDERS

Chlamydia (kla-MI-dee-ah): Sexually transmitted disease caused by a bacterium.

Endometriosis (en-doe-mee-tree-OH-sis): Condition in which bits of tissue similar to the endometrium grow in other parts of the body.

Gonorrhea (gah-nuh-REE-ah): A highly contagious sexually transmitted disease caused by a bacteria.

Syphilis (SIF-uh-lis): Sexually transmitted disease caused by a coil-shaped bacterium

Uterine fibroids (YOU-ter-in FIE-broydz): Also called myomas, benign (nonthreatening) growths of the muscle in the uterus.

Ovarian cancer

Ovarian cancer develops when cells in the ovaries become abnormal and grow uncontrollably, forming tumors. Ninety percent of all ovarian cancers develop in the cells that line the surface of the ovaries. This type of cancer is the fifth most common cancer among women in the United States. However, the death rate due to this cancer is higher than that of any other cancer among women.

Ovarian cancer can develop at any age, but more than half the cases occur in women who are sixty-five or older. It is difficult to diagnose ovarian cancer early because often there are no warning symptoms. Also, the disease spreads relatively quickly.

The actual cause of ovarian cancer is not known. However, several risk factors are known to increase a woman's chances of developing the disease. These factors include age, race (cancer is highest among white women), a high-fat diet, a family history of ovarian cancer, and having a first period at a young age, or going through menopause at a late age.

In the early stages of ovarian cancer, there may be no noticeable symptoms. Later, a woman may experience pain or swelling in the abdomen, constipation, vomiting, loss of appetite, fatigue, and unexplained weight gain.

If cancer is detected, surgery is the main treatment. The type of surgery depends on the extent of the disease. In most cases, the ovaries, uterus, and fallopian tubes are completely removed. In rare cases, only one ovary may be removed with the uterus and fallopian tubes left intact. After surgery, chemotherapy (using a combination of drugs to kill any remaining cancer cells and shrink any tumors) is usually administered.

More than 50 percent of the women who are diagnosed with ovarian cancer die within five years. If the disease is diagnosed before it has spread beyond an ovary, more than 90 percent of those women will survive five years or more. Since ovarian cancer cannot be prevented, the American Cancer Society recommends that all women over the age of forty undergo annual pelvic examinations to increase the chance of detecting the disease early.

Prostate cancer

Prostate cancer develops when cells in the prostate gland become abnormal and grow uncontrollably, forming tumors. It is the most common cancer among men in the United States, and it is the second leading cause of cancer deaths. Prostate cancer affects African American men twice as often as it does white men. In fact, African Americans have the highest rate of prostate cancer in the world.

Prostate cancer is found mainly in men over the age of fifty-five. As men grow older, the chance of developing the disease increases. Although the cause of this type of cancer is unknown, evidence suggests that age, race, a high-fat diet, and increased blood levels of testosterone may play a part in the development of the disease.

Frequently, prostate cancer has no symptoms. When the tumor is enlarged or the cancer has spread, the following symptoms may appear: weak or interrupted urine flow, frequent urination (especially at night), difficulty starting urination, inability to urinate, pain or burning sensation when urinating, blood in the urine, persistent pain in the lower back, and painful ejaculation.

If prostate cancer is detected (either through a rectal examination or blood test), surgery to remove the prostate gland completely is the most common treatment. The seminal vesicles are also removed during the procedure. If the prostate cancer is detected at an early stage, radiation therapy (using X rays or other high-energy rays to kill cancer cells and shrink any tumors) may be used instead of surgery. Chemotherapy (using a combination of drugs to kill any remaining cancer cells and shrink any tumors) is sometimes used to treat prostate cancer that has recurred after initial treatments.

Nearly 87 percent of men who are treated for prostate cancer survive. If the disease is detected early, that percentage increases. Prostate cancer cannot be prevented. To increase the chance of detecting the disease early, the American Cancer Society recommends that all men over the age of forty have an annual rectal examination (men over the age of fifty should have a blood test, in addition).

Sexually transmitted diseases

Sexually transmitted diseases (also called STDs or venereal diseases) are infections transmitted through various forms of sexual activity. More than twenty-five STDs exist, caused by many different organisms. About 12 million new STD infections occur in the United States each year. Almost 65 percent of all STD infections affect people under the age of twenty-five.

STDs can cause birth defects, blindness, brain damage, cancer, heart disease, infertility, mental retardation, and death. Symptoms of STDs vary according to the virus or bacteria causing the disease and the body system affected. In general, a woman who has an STD may bleed when she is not menstruating. She may also have an abnormal vaginal discharge. In addition, vaginal burning, itching, and odor are common. A man afflicted with an STD may have a discharge from the tip of his penis. Urinating may also cause a painful or burning sensation. Both women and men may develop skin rashes, sores, bumps, or blisters near the mouth, genitals, or anal area.

Perhaps the most deadly and frightening STD is AIDS or acquired immune deficiency syndrome. It is caused by the human immunodeficiency virus or HIV. The virus is transmitted between humans in blood, semen, and vaginal secretions. The two main ways to contract the virus are by sharing a needle with a drug user who is HIV-positive (infected with the virus) or by having unprotected sexual relations with a person who is HIV-positive. (For a more detailed discussion of HIV and AIDS, see chapter 5.)

Other common and potentially serious STDs in the United States include chlamydia, genital herpes, genital warts, gonorrhea, and syphilis.

Chlamydia is the most common STD in the United States. It is caused by a microscopic organism that lives as a parasite in human cells. It is transmitted through vaginal intercourse. A common symptom for both men and women is frequent and painful urination. The disease can be successfully treated with antibiotics.

Genital herpes is an incurable infection caused by a virus that is similar to the one responsible for cold sores. The infection is marked by the formation of fluid-filled, painful blisters in the genital area. The virus stays in the body for life. Over 25 million people in the United States are infected with the disease. It can be transmitted by oral and vaginal intercourse. Drugs are available to lessen symptoms and reduce outbreaks of the disease.

Genital warts, also called venereal warts, are caused by a virus that produces growths (warts) on the skin. In women, the growths occur on the genitals and on the walls of the vagina and cervix. In men, they develop in the urethra and on the shaft of the penis. The disease is transmitted by sexual contact. In addition to the visible warts, bleeding, pain, and odor are common symptoms. No treatment for genital warts is completely effective because it is necessary to destroy the skin infected by the virus.

Gonorrhea, commonly referred to as "the clap," is a highly contagious STD caused by a bacteria. It is transmitted through vaginal and anal intercourse. In men, the disease begins as an infection of the urethra. In women, it will most likely infect the cervix. If left untreated, the disease can travel through the reproductive tract (causing sterility) and spread to the bloodstream, infecting the brains, heart valves, and joints. Symptoms of the disease in women include bleeding between menstrual periods, painful urination, abdominal pain, and a cloudy and yellow vaginal discharge. Symptoms in men include painful and frequent urination and a thick, cloudy discharge from the penis. Gonorrhea is usually treated with a variety of antibiotics, but the bacteria that causes it is developing an increased resistance to routine medications.

Syphilis is an infectious disease caused by a coil-shaped bacterium. Spread by vaginal and anal intercourse, syphilis has been a public health problem since the sixteenth century. It currently affects an estimated 50 million people worldwide. The earliest symptom in both women and men is a chancre sore in the mouth or on the genitals. The fluid in the sore is very infectious. Lymph nodes near the chancre swell in most people afflicted with

the disease. As syphilis progresses, lymph nodes in the armpits, groin, and neck areas may also swell and skin lesions may erupt. If not treated, syphilis may cause damage years later to the heart and blood vessels, lungs, and central nervous system. The disease is usually treated with sufficiently large doses of antibiotics such as penicillin.

Testicular cancer

Testicular cancer develops when cells in the testes become abnormal and grow uncontrollably, forming tumors. Although a rare type of cancer, it often grows very quickly. It is the most common type of cancer to occur in young males under the age of thirty. The cause of testicular cancer is unknown.

This type of cancer usually shows no early symptoms. A mass in the testes usually indicates testicular cancer, but this may not be true in every case. In advanced stages of the cancer, symptoms include lower back pain, difficulty in urinating, a cough, and breathing problems. Sometimes there is pain in the testes.

HINTON'S FIGHT AGAINST SYPHILIS

William Augustus Hinton (1883–1859), the first African American professor at Harvard Medical School, earned an international reputation as a medical researcher for his work on the detection and treatment of sexually transmitted diseases. He was integral in developing two common diagnostic (identification) procedures for syphilis, the Hinton test and the Davies-Hinton test.

From the time he graduated from Harvard Medical School in 1912 until his retirement, Hinton concentrated his research on the diagnosis and treatment of syphilis. The first diagnostic test for the disease had been developed by German physician August von Wassermann in 1906. However, the test took two days to complete. In 1923, a Russian-American researcher, Reuben Leon Kahn, produced a modified syphilis test that took only a few minutes to complete. However, these blood tests for the disease often resulted in false diagnoses and consequent medical mistreatments.

In 1927, Hinton perfected a syphilis test—subsequently known as the Hinton test—that was simpler, less expensive, and more accurate than the previous procedures. As a result, the Hinton test was adopted as the standard method for diagnosing syphilis. Later, with J. A. V. Davies, Hinton developed an even more accurate diagnostic test, the Davies-Hinton test. In 1936, Hinton wrote Syphilis and Its Treatment, in which he outlined correct procedures for using laboratory tests for syphilis. Although the book at first had little support in the medical community, within twenty years it had become widely accepted and acclaimed.

If testicular cancer is discovered, surgery to remove the mass is the first line of treatment. If the cancer has spread to other parts of the body, chemotherapy (using a combination of drugs to kill any remaining cancer cells and shrink any tumors) or radiation therapy (using X rays or other high-energy rays to kill any remaining cancer cells and shrink any tumors) or a combination of both may be used following surgery.

The cure rate for testicular cancer that has not spread is 95 percent. Since the cancer cannot be prevented, it is important for men to perform regular examinations of their testes in order to detect any mass at an early stage.

Uterine cancer

Uterine cancer, also called endometrial cancer, develops when cells of the endometrium become abnormal and grow uncontrollably, forming tumors. It is a common type of cancer among women, generally occurring in those women who have gone through menopause and are forty-five years old or older.

The exact cause of uterine cancer is unknown. Medical researchers believe, however, that several factors increase a woman's chance of developing this type of cancer. Among those factors are age, obesity, diabetes, high blood pressure, irregular menstrual periods, family history of uterine cancer, and having a first period at a young age or going through menopause at a late age.

Symptoms of uterine cancer are present at an early stage in the disease. The most common symptom is unusual bleeding or discharge from the vagina. Pain and the presence of a lump or mass in the pelvic region are symptoms that occur late in the disease.

If uterine cancer is discovered, the standard treatments are surgery, radiation therapy, chemotherapy, and hormonal therapy. The type of procedure used depends on the stage of the disease. When the disease is detected early, surgery to remove the uterus is the procedure most often employed. This type of surgery is called a hysterectomy. If the cancer has spread, the ovaries and fallopian tubes are also surgically removed. Radiation therapy (using X rays or other high-energy rays to kill any cancer cells and shrink any tumors) may be used in place of or in addition to surgery. Chemotherapy (using a combination of drugs to kill any cancer cells and shrink any tumors) is usually reserved for women with advanced or recurrent uterine cancer. In hormonal therapy, drugs similar to the hormone progesterone are give to help slow the growth of endometrial cells. Again, this procedure is usually reserved for women with advanced or recurrent uterine cancer.

If uterine cancer is found and treated in its early stages, approximately 96 percent of women so treated survive five years or more. That survival rate falls to 66 percent if the cancer has spread before it is treated. Early detection is extremely important in helping to cure this disease. Controlling obesity, high blood pressure, and diabetes may also help to reduce the risk of developing uterine cancer.

Uterine fibroids

Uterine fibroids, also called myomas, are benign (nonthreatening) growths of the muscle in the uterus. They are not cancerous, nor are they related to cancer. Uterine fibroids are extremely common. They usually develop in women between the ages of thirty and fifty. About 25 percent of the women in this age group have noticeable fibroids.

No one knows exactly what causes fibroids, which grow in three locations: in the uterine cavity, on the wall of the uterus, and on the outside of the uterus. Not all fibroids cause symptoms, but when they do, the symptoms include the following: heavy uterine bleeding, pelvic pressure and pain, and complications during pregnancy.

Even fibroids that do cause symptoms may not require treatment. When the fibroids grow large enough to cause serious problems, surgery may be necessary. The only real cure for fibroids is the surgical removal of the uterus,

a procedure called a hysterectomy. If only the fibroids are removed and the uterus is repaired and left in place, the surgical procedure is called a myomectomy.

Uterine fibroids cannot be prevented. Luckily, many women who have fibroids have either no symptoms or only minor symptoms. Unfortunately, fibroids tend to grow over time, and many women ultimately decide to have some form of treatment.

TAKING CARE: KEEPING THE REPRODUCTIVE SYSTEM HEALTHY

As humans age, the functioning of their reproductive systems decline. Although testosterone and sperm continue to be produced in men, both decrease with advancing age. For women, there is a definite end to the ability to reproduce. With menopause, estrogens levels decrease and ovulation and menstrual cycles cease.

It is important, then, to keep the reproductive system operating at peak efficiency. As in all other body systems, the following play a key part: eating a proper diet low in fat and high in fiber, maintaining a healthy weight, consuming proper amounts of good-quality drinking water, getting adequate rest, engaging in regular exercise, not smoking or taking illegal drugs, drinking only moderate amounts of alcohol (if at all), and reducing stress levels.

Stress taxes all body systems. Any condition that threatens the body's homeostasis or steady state is a form of stress. Conditions that cause stress may be physical, emotional, or environmental. Stress can be particularly taxing on the reproductive system. In women, long-term stress can interrupt or even stop the menstrual cycle. In men, long-term stress can reduce the number of sperm produced or cause impotence. Combining exercise with proper amounts of sleep, relaxation techniques, and positive thinking will help reduce stress and prevent these disorders.

Because the organs of the reproductive system are susceptible to infection, it is especially important to practice good hygiene by keeping the genital area clean. When engaging in sexual relations, it is vital to practice safe sex. This includes choosing a partner carefully and forming a monogamous relationship (having only one sexual partner). If an individual engages in sexual intercourse with numerous partners, that individual should be tested for any sexually transmitted disease. While having sex, a man should wear a latex condom (condoms for females have been developed). Wearing a condom will help prevent the spread of sexually transmitted diseases and prevent unwanted pregnancies. Of course, practicing abstinence (refraining from sexual activity) is the only sure way to prevent sexual diseases and pregnancies.

FOR MORE INFORMATION

Books

Avraham, Regina. The Reproductive System. New York: Chelsea House, 1991.

Parker, Steve, and Aziz Khan. Reproduction. Brookfield, CT: Copper Beech Books, 1998.

Parker, Steve. The Reproductive System. Austin, TX: Raintree/Steck-Vaughn, 1997.

Silverstein, Alvin, Virginia Silverstein, and Robert Silverstein. The Reproductive System. New York: Twenty-First Century Books, 1994.

WWW Sites

Cyber Anatomy: Reproductive System
http://tqd.advanced.org/11965/html/cyber-anatomy_reproductive.html
Site provides detailed information on the reproductive system that is divided into two levels: the first geared for students in grades 6–9, the other for students in grades 10–12. In each of those levels, textual information and illustrations are presented separately for the female and male reproductive systems.

Human Reproduction
http://www.epigee.org/guide/reproduction.html
Site gives a clear description of the process of the female reproductive system, ovulation, and contraception. Also provides a short list of recommended books and a few links to other sites.

Reproductive System
http://hyperion.advanced.org/2935/Natures_Best/Nat_Best_Low_Level/Reproductive_page.L.html
Site offers an extensive discussion of the reproductive systems of both males and females with some illustrations (the high band width selection offers more illustrations).

The Reproductive System
http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookReprod.html
Site presents a detailed chapter on the reproductive system—both female and male parts—from the On-Line Biology textbook.

The Reproductive System
http://www.msms.doe.k12.ms.us/biology/anatomy/reproductive/reproductive.html
Site provides links to pages offering text and illustrations that describe the organs and accessory parts of the female and male reproductive systems and how they function.

Sexually Transmitted Diseases
http://www.epigee.org/guide/stds.html
Site provides links to discussions of the most common sexually transmitted diseases, along with consequences, preventions, tips, and related links.