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CHAPTER OUTLINE
21.1 Male Reproductive System
The male gonads are paired testes.
Genital Tract
Sperm produced by the testes mature within the epididymides. When sperm leave an
epididymis, they enter a vas deferens and then into an ejaculatory duct. The ejaculatory
ducts connect to the urethra. At the time of ejaculation, sperm leave the penis in fluid
called semen. The penis is the male organ of sexual intercourse.
Erection and Orgasm in Males
When a man is sexually excited, the arteries in the penis relax and widen resulting in an
erection. The contractions that expel semen from the penis are a part of male orgasm, the
physiological and psychological sensations that occur at the climax of sexual stimulation.
Male Gonads, the Testes
The testes, which produce sperm and male sex hormones, lie outside the abdominal
cavity of the human male within the scrotum.
Seminiferous Tubules
The seminiferous tubules are packed with cells undergoing spermatogenesis,
the production of sperm.
Interstitial Cells
The male sex hormones are secreted by interstitial cells that lie between the
seminiferous tubules.
Hormonal Regulation in Males
The hypothalamus has ultimate control of the testes’ sexual function because it secretes a
hormone called gonadotropin-releasing hormone that stimulates the anterior pituitary
to secrete the two gonadotropic hormones, follicle-stimulating hormone and luteinizing
hormone in both males and females. Testosterone is the main sex hormone in males and
is essential for the development of the male reproductive organs and secondary sex
characteristics.
21.2 Female Reproductive System
The female gonads are paired ovaries within the upper pelvic cavity. Ovulation is the process by
which an oocyte, the female gamete, bursts from an ovary and usually enters a uterine tube.
The Genital Tract
The uterine tubes extend from the uterus to the ovaries. The uterus is a thick-walled,
muscular organ where an oocyte develops into an embryo. At the lower end of the uterus
the cervix connects to the outside through the vagina.
External Genitals
The external genital organs of the female are known collectively as the vulva.
Orgasm in Females
Although the vagina is the organ of sexual intercourse in females, the clitoris plays a
significant role in the female sexual response.
21.3 Ovarian and Uterine Cycles
Hormone levels cycle in the female on a monthly basis and the ovarian cycle drives the uterine
cycle.
The Ovarian Cycle
The ovary contains many follicles, each one containing an immature oocyte. The ovarian
cycle occurs as a follicle changes from a primary to a secondary to a vesicular follicle. As
the follicle matures, oogenesis is initiated and continues. The secondary oocyte enters a
uterine tube.
Phases of the Ovarian Cycle
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The first half of the ovarian cycle is called the follicular phase and the second
half is the luteal phase. Ovulation separates the two phases, occurring at about
the 14th day of a 28-day cycle.
The Uterine Cycle
The female sex hormones estrogen and progesterone affect the uterine endometrium,
causing the uterus to undergo a cyclical series of events known as the uterine cycle.
Menstruation
Menstruation results when the endometrium disintegrates and passes from the body
along with mucus and blood.
Fertilization and Pregnancy
If fertilization does occur, an embryo begins development even as it travels down the
uterine tube to the uterus. The embryo will implant into the lining of the uterus. The
placenta sustains the developing embryo and later fetus.
Menopause
Menopause is the period in a woman’s life during which the ovarian and uterine
cycles cease. It is accompanied by hormonal changes that often produce
uncomfortable physical symptoms.
21.4 Control of Reproduction
Birth control methods are used to regulate the number of children an individual or couple will
have.
Birth Control Methods
The most reliable method of birth control is abstinence. Contraceptives are medications
and devices that reduce the chance of pregnancy. Emergency contraception includes
approaches to birth control to prevent pregnancy after unprotected intercourse.
21.5 Sexually Transmitted Diseases
Many infectious diseases are transmitted by sexual contact and are therefore called sexually
transmitted diseases.
STDs Caused by Viruses
Viruses do not respond to traditional antibiotics. Antiviral drugs have been developed to
treat some, but in many cases infection is lifelong.
AIDS
Acquired immunodeficiency syndrome (AIDS) is caused by HIV (human
immunodeficiency virus). AIDS is considered a pandemic. HIV is transmitted by
sexual contact with an infected person and by needle-sharing.
Stages of an HIV Infection
Upon initial infection, the HIV virus replicates at a high level. Most
people have only mild symptoms at this stage. Usually no other HIVrelated symptoms occur for several years. Eventually the patient begins
to suffer from opportunistic infections because the immune system is
weakened.
Treatments for HIV Infection
There is still no cure for HIV infection, but an increasing number of
drugs have become available to help control the replication and spread of
HIV. Five classes of antiretroviral drugs are currently available.
HIV Vaccines
It is unlikely that the global HIV pandemic will ever be controlled unless
an effective vaccine against HIV is developed. Vaccine trials are
currently being conducted in several countries.
Genital Herpes
Genital herpes is caused by the herpes simplex virus. It is one of the more
prevalent sexually transmitted diseases and results in recurring symptoms.
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Human Papillomavirus
There are over 100 types of human papillomaviruses (HPV). About ten types can
cause cervical cancer. Most strains cause warts. Early detection of cervical
cancer is possible by means of a Pap test. A vaccine is available that is effective
against the four most common types of HPV, including the two types that cause
about 70% of cervical cancers.
Hepatitis B
Hepatitis B causes inflammation of the liver. A safe and effective vaccine is
available for hepatitis B.
STDs Caused by Bacteria
Bacterial diseases are usually curable with appropriate antibiotic therapy if diagnosed
early enough.
Chlamydia
Chlamydia is caused by the bacterium Chlamydia trachomatis. New chlamydial
infections are more numerous than any other STD. If not properly treated in
women, the infection can cause pelvic inflammatory disease (PID) which may
result in sterility.
Detection and Treatment of Chlamydia
New and faster laboratory tests are available for detecting a chlamydial
infection, but their expense sometimes prevents public clinics from
testing for it.
Gonorrhea
Gonorrhea is caused by the bacterium Neisseria gonorrhoeae. As many as 20%
of infected males are asymptomatic. Unfortunately, 60–80% of females are
asymptomatic until they develop severe PID.
Syphilis
Syphilis is caused by the bacterium Treponema pallidum. The disease has three
stages, the last of which results in death. Antibiotics are effective in treating
syphilis, especially in the early stages.
21.6 Other Disorders of the Reproductive System
Several common disorders affect the reproductive system.
Common Conditions Affecting the Male Reproductive System
Erectile Dysfunction
Erectile dysfunction or impotence is the inability to produce or maintain an
erection sufficient to perform sexual intercourse. It is estimated that about 50%
of men aged 40 to 75 have experienced some degree of ED.
Disorders of the Prostate
Beginning around age 40, most men have some enlargement of the prostate
gland. Disorders of the prostate include benign prostatic hyperplasia and
prostate cancer.
Testicular Cancer
Testicular cancer is the most common type of cancer in males aged 15–35. Men
should perform a monthly testicular self-examination.
Common Conditions Affecting the Female Reproductive System
Endometriosis
Endometriosis, the presence of endometrial-like tissue at locations outside the
uterine cavity, is the most common cause of chronic pelvic pain in women.
Ovarian Cancer
Ovarian cancer typically occurs in individuals over the age of 40 and has a
worse prognosis than testicular cancer.
Disorders of Menstruation
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Abnormalities include too little bleeding or too much bleeding. The most
common disorder of menstruation is dysmenorrhea, or painful menstruation.
Premenstrual syndrome (PMS) is a group of symptoms related to the menstrual
cycle.
Infertility
Infertility is the failure of a couple to achieve pregnancy after one year of regular,
unprotected intercourse.
Causes of Infertility
The most frequent cause of infertility in males is low sperm count and/or a large
proportion of abnormal sperm. Common causes of infertility in females include
blocked uterine tubes due to PID and endometriosis. Infertility problems also
begin to increase after age 35 in women. Obesity has been linked to infertility in
both genders.
Assisted Reproductive Technologies
Assisted reproductive technologies are techniques that increase the changes of
pregnancy.
Artificial Insemination by Donor (AID)
During artificial insemination, sperm are placed in the vagina by a
physician.
In Vitro Fertilization (IVF)
In IVF, conception occurs in laboratory glassware.
Gamete Intrafallopian Transfer (GIFT)
The method is exactly the same as in vitro fertilization, except the
oocytes and the sperm are placed in the uterine tubes immediately after
they have been brought together.
Surrogate Mothers
In some instances, women are contracted and paid to have babies.
Intracytoplasmic Sperm Injection (ICSI)
In this highly sophisticated procedure, a single sperm is injected into an
oocyte.
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