CONCEPTS IN BIOLOGY

PART VI. PHYSIOLOGICAL PROCESSES

27. Human Reproduction, Sex, and Sexuality

27.12. Changes in Sexual Function with Age

Although there is a great deal of variation, at about age 50, a woman’s hormonal balance begins to change because of changes in the ovaries’ production of hormones. At this time, the menstrual cycle becomes less regular and ovulation is often unpredictable. Over several years, the changes in hormone levels cause many women to experience mood swings and physical symptoms, including cramps and hot flashes. Menopause is the period when a woman’s body becomes nonreproductive, because reproductive hormones stop being produced. This causes the ovaries to stop producing eggs, and menstruation ends. Occasionally, the symptoms associated with menopause become so severe that they interfere with normal life and the enjoyment of sexual activity. A physician might recommend hormone replacement therapy (HRT) which involves administering either estrogen alone or estrogen and progestin together, to augment the natural production of estrogen and progesterone. Normally, the sexual enjoyment of a healthy woman continues during menopause and for many years thereafter.

Although human males do not experience a relatively abrupt change in their reproductive or sexual lives, recent evidence indicates that men also experience hormonal and emotional changes similar to those seen as women go through menopause. As men age, their production of sperm declines and they may experience a variety of problems related to their sexuality. The word i mpotence is used to describe problems that interfere with sexual intercourse and reproduction. These may include a lack of sexual desire, problems with ejaculation or orgasm, and erectile dysfunction (ED). Erectile dysfunction is the recurring inability to get or keep an erection firm enough for sexual intercourse. Most incidences of ED at any age are physical not psychological. In older men, this is usually the result of injury, disease, or the side effects of medication. Damage to nerves, arteries, smooth muscles, and other tissues associated with the penis is the most common cause of ED. Diseases linked with ED include diabetes, kidney disease, chronic alcoholism, multiple sclerosis, atherosclerosis, vascular disease, and neurologic disease. Blood pressure drugs, antihistamines, antidepressants, tranquilizers, appetite suppressants, and certain ulcer drugs have been associated with ED. Other possible causes are smoking, which reduces blood flow in veins and arteries, and lowered amounts of testosterone. ED is frequently treated with psychotherapy, behavior modification, oral or locally injected drugs, vacuum devices, and surgically implanted devices. ED is not an inevitable part of aging. Rather, sexual desires tend to wane slowly as men age. They produce fewer sperm cells and less seminal fluid. Nevertheless, healthy individuals can experience a satisfying sex life during aging.

Human sexual behavior is quite variable. The same is true of older persons. The range of responses to sexual partners continues, but generally in a diminished form. People who were very active sexually when young continue to be active, but less so as they reach middle age. Those who were less active tend to decrease their sexual activity also. It is reasonable to state that one’s sexuality continues from before birth until death.

27.12. CONCEPT REVIEW

25. What is menopause?

26. How does sexual function change with age?

Summary

The human sex drive is a powerful motivator for many activities in our lives. Although from a biological perspective it provides for reproduction and generates new gene combinations, it also has a nonbiological, sociocultural dimension. Sexuality begins before birth, as sexual anatomy is determined by the sex-determining chromosome complement received at fertilization. Females receive 2 X chromosomes. A male receives 1 X and 1 Y sex-determining chromosome. It is the presence of the Y chromosome that causes male development and the absence of a Y chromosome that allows female development.

At puberty, hormones stimulate the maturation of the ovaries and testes and the development of secondary sex characteristics. As the ovaries and testes begin to produce gametes, fertilization becomes possible. Sexual reproduction involves the production of gametes by meiosis in the ovaries and testes. The production and release of these gametes is controlled by the interaction of hormones. In males, each cell that undergoes spermatogenesis results in four sperm; in females, each cell that undergoes oogenesis results in one egg and two polar bodies. Humans have specialized structures for the support of the developing embryo, and many factors influence its development in the uterus. Sexual reproduction depends on proper hormone balance, proper meiotic division, fertilization, placenta formation, proper diet of the mother, and birth. Hormones regulate ovulation and menstruation and can be used to encourage or discourage ovulation. Fertility drugs and birth-control pills, for example, involve hormonal control. In addition to the pill, a number of contraceptive methods have been developed, including the diaphragm, condom, IUD, spermicidal jellies and foams, contraceptive implants, the sponge, tubal ligation, and vasectomy.

Hormones continue to direct our sexuality throughout our lives. Even after menopause, when fertilization and pregnancy are no longer possible for a female, normal sexual activity can continue in both men and women.

Basic Review

1. All the factors that contribute to one’s female or male nature are referred to as _____.

2. Humans have a total of _____ chromosomes, _____ of which are considered sex-determining.

a. 44, 2

b. 23, 2

c. 48, 4

d. 46, 2

3. In humans, the _____ acts as a master switch, triggering the events that convert an embryo into a male.

a. SRY gene

b. TDF gene

c. Y-gene

d. Turner’s gene

4. Men with Klinefelter’s syndrome may be sterile and show breast enlargement, an incomplete masculine body form, a lack of facial hair, and some minor learning problems. (T/F)

5. Semen is produced by the testes. (T/F)

6. Gonadotropin-releasing hormone (GnRH) is produced by the

a. hypothalamus.

b. pituitary.

c. testes.

d. corpus leuteum.

7. Birth control pills contain hormones. (T/F)

8. The unequal division that occurs during oogenesis results in the formation of smaller cells that do not develop into true eggs, called _____.

9. If a woman normally has a regular 21-day menstrual cycle, ovulation occurs about day _____ in the cycle.

10. If an embryo splits during cleavage into two separate groups of cells, _____ twins may develop.

11. Transgender individuals have a psychological view of themselves that is different from their physical bodies. (T/F)

12. Homosexuality appears to have a genetic basis. (T/F)

13. The cells released during ovulation

a. are diploid.

b. were present in the ovaries for several years.

c. contain Y chromosomes.

d. None of the above is correct.

14. The hormone progesterone is produced by the

a. corpus luteum.

b. pituitary.

c. hypothalamus.

d. uterus.

15. Fertilization of an egg usually takes place in the _____.

Answers

1. sexuality 2. d 3. a 4. T 5. F 6. a 7. T 8. polar bodies 9. 7. 10. identical 11. T 12. T 13. b 14. a 15. oviduct (fallopian tube)

Thinking Critically

Hormones in the Environment

The practice of medicine has increasingly moved in the direction of using medications containing steroids to control disease or regulate function, as in birth-control pills. To meet these demands, the pharmaceutical industry produces enormous amounts of these drugs. However, what happens to these drugs once they enter the body? Although some of the drug is destroyed in controlling disease or regulating a function, such as ovulation, a certain amount is not and is excreted. There is some concern about the amount of medical steroids entering the environment in this way. What effects might they have on the public, who unintentionally ingest these as environmental contaminants? Consider the topics of sexual reproduction, the regulation of hormonal cycles, and fetal development, and explain (1) how you would determine “acceptable levels” of such contaminants, (2) what might happen if these levels were exceeded, and (3) what steps might be taken to control such environmental contamination.