13 - Reproduction

pituitary gland

"Releasing hormones" from the hypothalamus signal the release of hormones from a pea-sized endocrine gland in the brain, called the pituitary gland (pih TOO ih tehr ee). The pituitary controls many of your body's functions. These functions include growth, reproduction, and metabolism. Metabolism is the process by which you obtain energy from food. Some pituitary hormones act as "on" switches for other endocrine glands. For example, one pituitary hormone signals the thyroid gland to release hormones essential for normal metabolism. Other pituitary hormones control body activities directly. For example, growth hormone released by the pituitary gland regulates growth throughout your body from infancy to adulthood.

hormones

A chemical substance produced by an endocrine gland is known as a hormone. You can think of a hormone as a chemical messenger. Each hormone has a specific function and specific "targets" in the body. Once released into the bloodstream, a hormone travels to its target cells, where it turns on, turns off, speeds up, or slows down the activities of those cells. For example, targets of the hormone adrenaline include cells in your heart, muscles, and brain. Adrenaline causes a faster heartbeat, tensing of the muscles, and increased alertness—your "fight-or-flight" response The endocrine system is kept in balance by the coordinated action of various hormones. For example, a hormone from one gland may turn on the production of a different hormone by a second gland. In turn, the hormone from the second gland signals the first gland to stop releasing its hormone. By this system of checks and balances, the endocrine system keeps the body's activities functioning smoothly.

keeping healthy

A number of medical conditions can affect the female reproductive system. Teens who adopt healthy habits can reduce their risk of problems. Caring for the female reproductive system involves cleanliness, sexual abstinence, prompt treatment for infections, self-exams, and regular medical checkups.

keeping healthy

A number of medical conditions can affect the male reproductive system. However, teens who adopt healthy habits can reduce their risk of problems. Caring for the male reproductive system involves cleanliness, sexual abstinence, protection from trauma, self-exams, and regular medical checkups.

sexual abstinence

A number of serious infections can result from sexual contact. Healthy choices regarding sexual behavior can prevent such infections. The only way to eliminate your risk of sexually transmitted infections is to abstain from sexual activity.

sexual abstinence

A number of serious infections of the reproductive system and other body systems can result from sexual contact. Healthy choices regarding sexual behavior can prevent such infections. The only way to eliminate your risk of sexually transmitted infections is to abstain—or refrain from—sexual activity. In other words, practice sexual abstinence.

toxic shock syndrome

A rare but serious medical condition associated with tampon use is toxic shock syndrome. This syndrome is caused by a bacterial infection. Symptoms of toxic shock syndrome include a sudden high fever, a rash, vomiting, diarrhea, and dizziness. Because toxic shock syndrome can lead to death, a woman with any of these symptoms during her period should seek medical attention immediately. To decrease the risk of toxic shock syndrome, women should use tampons with the lowest possible absorbency for their needs and change tampons often.

medical checkups

A yearly checkup of the reproductive system is recommended for all females who have reached puberty. During the exam, the doctor will examine the breasts and genitals and may perform a pelvic exam and a Pap smear. In a Pap smear, a sample of cells is taken from the cervix and examined under a microscope. Pap smears can detect cancer of the cervix. Starting at about age 40, women may get a mammogram, an X-ray of the breast that can help detect breast cancer. A woman with a family history of breast cancer or other risk factors may have her first mammogram at a younger age. A mammogram may detect cancers that are too small for a woman or her doctor to feel in a breast exam. A doctor can also detect and treat other reproductive problems, including cancers of the ovary or uterus, and Ovarian cysts Ovarian cysts are growths on the ovary. Large ones may be painful and need to be surgically removed. Endometriosis This is a condition in which tissue from the lining of the uterus—the endometrium—grows outside the uterus, in the pelvic cavity. This condition can be very painful and is usually treated with hormones or surgery. Infertility Causes of infertility in women include blocked fallopian tubes and problems with ovulation.

menstrual cycle

As you learned, males typically produce millions of sperm cells every day after reaching puberty. Females, on the other hand, usually produce only one mature egg cell each month during a process called the menstrual cycle (MEN stroo ul). During the menstrual cycle, an ovary releases a mature egg. The egg travels to the uterus. If the egg is not fertilized, the uterine lining is shed and a new cycle begins.

other structures

Besides the external structures of the male reproductive system, there are internal ducts and accessory glands that play an important role in storing and releasing sperm.

stages of menstrual cycle

During the first half of the cycle, an egg matures inside one of the ovaries. Meanwhile, the lining of the uterus thickens. At about the middle of the cycle—typically on day 14—ovulation occurs. The mature egg is released by the ovary and travels into the fallopian tube. A female is most fertile, or able to become pregnant, around the time of ovulation. It takes about seven days for the egg to travel through the fallopian tube into the uterus. During this time the uterine lining continues to thicken, and the blood supply to it increases. If the egg has not been fertilized by the time it reaches the uterus, the uterine lining breaks down. The blood and tissue of the thickened lining pass out of the body through the vagina in a process called menstruation, or the menstrual period. As menstruation is taking place, another egg begins to mature in one of the ovaries. Thus menstruation marks the end of one cycle and the beginning of another. In general, a menstrual period lasts about 3 to 5 days. Most women wear either a sanitary pad or a tampon to absorb the menstrual flow.

menstrual discomfort

During the menstrual period, some women may experience abdominal cramps or other discomfort. Cramps are caused by contractions of the uterus. For severe cramps or for any other menstrual concerns, women should see a medical professional. Some women experience discomfort for a time before their menstrual period. This condition, known as premenstrual syndrome, or PMS, is marked by nervous tension, mood swings, headaches, bloating, and irritability. The dramatic change in hormone levels that occurs before menstruation begins may cause PMS. Some doctors recommend that PMS sufferers reduce their intake of salt, sugar, and caffeine, get regular exercise, and try other stress-reduction techniques.

functions of endocrine glands

Each of your endocrine glands plays a specific, important role in your body. The endocrine glands include the hypothalamus, pituitary gland, thyroid gland, parathyroid glands, thymus gland, adrenal glands, pancreas, and reproductive glands.

other endocrine glands

Endocrine glands are found throughout the body. Use the interactive figure to see the location and function of the different endocrine glands in the body. The reproductive glands are an important part of the endocrine system. In males, the reproductive glands consist of two testes, and in females, two ovaries. The reproductive glands work at low levels in both boys and girls until about the age of ten, when puberty typically begins. Puberty is the period of sexual development during which a person becomes sexually mature and physically able to reproduce. Puberty starts when the hypothalamus signals the pituitary gland to begin producing two hormones. Those hormones in turn signal the reproductive glands to produce sex hormones. Sex hormones activate several changes in your outward appearance during puberty. Sex hormones also control reproductive functions inside your body. You will learn more about the reproductive glands and their hormones in the next two lessons.

protection from trauma

Good health also requires protection and prevention. During athletic activities, males should wear a protector, also called a "cup," or supporter. Tight clothing should be avoided, since tight pants or underwear can irritate or cause pain in the groin area. Males should also be careful when lifting heavy objects. Pressure in the abdomen during lifting can push a loop of intestine out of the area that usually contains it, causing a hernia. An inguinal (ING gwuh nul) hernia results if part of the intestine pushes into the scrotum. Surgery is almost always necessary to correct an inguinal hernia.

cleanliness

Healthy habits start with cleanliness. It is important to thoroughly clean the external organs—the penis and scrotum—daily, preferably during a shower or bath. Each day, an uncircumcised male should gently pull the foreskin back to clean the head of the penis. Drying the groin area well after showering can prevent fungal infections that can cause jock itch.

What is the endocrine system?

How much have you grown in the past year? When will you reach your adult height? Your growth rate is one of the many functions controlled by your body's endocrine system. The endocrine system regulates long-term changes in the body such as growth and development. It also controls many of your body's daily activities. Two examples of daily activities include your body's use of energy from a meal and its response to stress.

self-exams

It is important for males to monitor their own bodies for any signs of possible medical problems. Pain when urinating, unusual discharges, or sores on the genitals require a medical examination. Such conditions should not be self-treated. Males, especially teens and young men, should also examine their testes for signs of testicular cancer. Almost a third of testicular cancer cases occur in young men in their teens and twenties. As with all cancers, treatment is most effective when the cancer is caught in its early stages.

self-exams

It is important for women to monitor their own bodies for signs of possible medical problems. Symptoms of vaginitis, sores on the genitals, or any unusual pain in the abdomen require a medical exam. A woman should also consult a doctor if she notices heavier bleeding than normal during menstruation, if her periods stop completely, or if she notices bleeding at times between her regular periods. For the early detection of breast cancer, all women, including teens, should perform a monthly breast self-examination.

medical checkups

Medical exams throughout life can help ensure reproductive health. In older men, the prostate may become enlarged or cancerous. An enlarged prostate does not necessarily indicate either disease or illness, but it can cause discomfort. Since the prostate gland surrounds the urethra, an enlarged prostate may make urination painful or difficult. If that happens, surgery is usually required. Starting at age 50, men are encouraged to be screened for prostate cancer. Prostate cancer is the second most common cause of cancer death of older men. Another condition a doctor can diagnose is infertility—the inability to reproduce. Infertility can affect both males and females. Male infertility is marked by the inability to produce healthy sperm or a low sperm count. Infertility can result from the exposure to certain chemicals, having mumps after puberty, or an undescended testis.

fallopian tubes

Now use the figure to locate the two fallopian tubes (fuh LOH pee un)—passageways that carry eggs away from the ovaries. When the ovary releases an egg during ovulation, the fingerlike ends of the fallopian tube draw the egg into the tube. Eggs, unlike sperm, cannot swim. Tiny hairlike extensions called cilia line the fallopian tube and sweep the egg toward the uterus. If sperm are present around the egg, it may be fertilized. The fallopian tubes are the site where fertilization usually occurs.

factors affecting the menstrual cycle

On average, a menstrual cycle lasts 28 days. However, cycles as short as 21 days or as long as 35 days can be normal for some individuals. The endocrine system controls the menstrual cycle. The hormones involved include FSH and LH, which are released by the pituitary gland, and estrogen and progesterone, which are released from the ovaries. Factors such as diet, stress, exercise, and weight gain or loss also affect the menstrual cycle. The menstrual cycle may be irregular at times, especially during puberty. Except during pregnancy, menstrual cycles occur each month from puberty until about the age of 45 to 55. At that time of life, called menopause, the ovaries slow down their hormone production and no longer release mature eggs. Gradually, the menstrual cycle stops, and the woman is no longer able to become pregnant.

sperm production

Once a male reaches puberty, millions of sperm are produced in his testes each day. Sperm production begins when the hypothalamus signals the pituitary gland to release two hormones—luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH signals the testes to begin making testosterone. Testosterone and FSH then signal the production of sperm. Sperm production continues throughout adulthood.

structure and function

One essential function of all living things is reproduction, the process by which organisms produce offspring. In humans, the process begins with the development of reproductive cells in the bodies of males and females. In males, the reproductive cells are called sperm. The functions of the male reproductive system are to produce sex hormones, to produce and store sperm, and to deliver sperm to the female reproductive system. There, a sperm cell may join with an egg in a process called fertilization. Under the right conditions, a fertilized egg develops into a baby.

cleanliness

One important health habit is cleanliness, including daily washing of the external vaginal area. Cleanliness is especially important during menstruation, as is the regular changing of sanitary pads or tampons. Feminine hygiene sprays, douches, and deodorant tampons are not necessary. In fact, they may be harmful if they cover up signs of an infection or cause irritation. If washing does not get rid of normal body odors, or if any unusual discharge is noted, seek medical attention.

prompt treatment for infections

Some infections of the reproductive system are not related to sexual behavior. Many women experience vaginitis, a vaginal infection caused by yeast, bacteria, or other microorganisms. Symptoms include a thick discharge, odors, vaginal itching, and a burning sensation during urination. Only a doctor can diagnose the specific cause of vaginitis and provide appropriate treatment.

release of sperm

The ejection of semen from the penis is called ejaculation. Ejaculation occurs when muscles in the male reproductive system and at the base of the bladder contract, forcing semen through the urethra. The urethra—a tube that passes through the penis to the outside of the body—carries urine as well as sperm, but not at the same time. A valve within the urethra prevents the two fluids from mixing. Several million sperm cells are released during one ejaculation. What happens to sperm that are not ejaculated? Sperm stored in the male reproductive system eventually degenerate, meaning they break down, and are disposed of. Ejaculation can occur when the penis is in an erect state. An erection is a condition in which the penis becomes larger and stiffer as blood chambers in the penis become filled with blood. An erection does not need to result in ejaculation—in fact, most do not. Erections can be caused by different factors, including sexual excitement or tight clothing. Sometimes an erection may occur for no apparent reason at all. This is especially common during puberty. It is also common for a teenage male to experience a nocturnal emission, or "wet dream," which is erection and ejaculation during sleep. Nocturnal emissions occur for various reasons, including sexually arousing dreams. They are a normal occurrence and may happen frequently. It is also normal not to experience nocturnal emissions.

hypothalamus

The hypothalamus (hy poh THAL uh mus), an endocrine gland located in the brain, is actually part of both the nervous and the endocrine systems. For example, nerve signals from the hypothalamus control body temperature and feelings of sleep and hunger, and hormones from the hypothalamus control the body's water levels. The hypothalamus also produces a class of hormones called "releasing hormones" that signal the release of hormones from another region of the brain

testes

The interactive figure shows the organs of the male reproductive system. Locate the two oval-shaped testes (TES teez), the male reproductive glands. The testes (singular, testis) have two major functions—the production of testosterone and the production of sperm. The sex hormone testosterone affects the production of sperm and signals certain physical changes at puberty, such as the growth of facial hair. The testes, also called testicles, hang outside the main body cavity, within a sac of skin called the scrotum. Because they are located outside the body, the temperature of the testes is a few degrees lower than the temperature inside the body. Sperm need this lower temperature to develop properly and survive. In some males, one or both of the testes may not descend into the scrotum before birth, a condition called undescended testis. Sperm will not develop properly in an undescended testis because the temperature is too high. The condition is also a risk factor for testicular cancer. Surgery is usually performed before age two to correct this condition.

penis

The penis is the external sexual organ through which sperm leave the body. The tip of the penis is covered with loose skin, called the foreskin. In some males the foreskin is removed shortly after birth. This surgical procedure is known as circumcision. The decision to circumcise an infant is usually based on cultural or religious reasons.

structure and function

The reproductive cells in males are called sperm. Female reproductive cells are called eggs, or ova (singular, ovum). The functions of the female reproductive system are to produce sex hormones, to produce eggs, and to provide a nourishing environment in which a fertilized egg can develop into a baby.

ovaries

The reproductive glands in which eggs are produced are called ovaries. The ovaries are located a few inches below the waist, one on each side of the body. Each ovary is about the size of an almond. Ovaries have two important functions: they produce the female sex hormones estrogen and progesterone, and they release mature egg cells. The sex hormone estrogen activates certain physical changes at puberty, such as breast development, and controls the maturation of eggs. Progesterone activates changes to a woman's reproductive system before and during pregnancy. When a girl is born, each ovary contains hundreds of thousands of immature eggs. The eggs begin to mature when the girl reaches puberty. Once puberty begins, one of the ovaries releases a mature egg about once every month in a process called ovulation.

uterus

The uterus is a hollow, muscular, pear-shaped organ. In the uterus, a fertilized egg can develop and grow. The uterus has several layers of tissue and a rich supply of blood that protect and nourish the developing baby. The narrow base of the uterus is called the cervix. When a baby is ready to be born, the cervix expands to allow the baby to pass through.

vagina

The vagina, or birth canal, is a hollow, muscular passage leading from the uterus to the outside of the body. Sperm enter a female's body through the vagina. During childbirth, the baby passes out of the mother's body through the vagina. The walls of the vagina are very elastic, which allows it to expand dramatically during childbirth.

endocrine glands

Your endocrine system is made up of a group of organs, called endocrine glands (EN duh krin). An endocrine gland produces and releases chemical substances that signal changes in other parts of the body. Some of your body's glands, such as sweat glands, release their chemicals into tiny tubes called ducts. The ducts carry the chemicals to the place where they will be used. Endocrine glands, on the other hand, do not have ducts. Instead, they release substances directly into the bloodstream. The blood then carries those substances throughout the body.

the pathway of sperm

through the male reproductive system, sperm cells mix with fluids produced by the prostate and two other glands. The mixture of sperm cells and these fluids is called semen (SEE mun).