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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 1 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. 2 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 3 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. 4