Human Sexuality

E

Adulthood

In adulthood, more permanent relationships, in the form of marriage or cohabitation, become prevalent. The frequency of sexual activity is different for different individuals. People in monogamous relationships often engage in sexual activity more frequently than those who have several partners. It is not unusual for some new couples to have sexual intercourse almost every day, but in general, among married or cohabiting couples, the frequency of sexual intercourse tends to decline the longer the two people are together.

Many individuals remain sexually active throughout their older years. According to Love, Sex, and Aging (1984), by American social historian Edward Brecher, a book about sex among older people in the United States, 33 percent of women 70 years of age and older and 43 percent of men in the same age range report that they still masturbate, and 65 percent of married women and 59 percent of married men in that age range report that they still have sexual intercourse with their spouses.

As people age, they may experience physical changes, illnesses, or emotional upheavals, such as the loss of a partner, that can lead to a decline in sexual interest and behavior. In women, there is a gradual decline in the function of the ovaries and in the production of estrogen. The average age at which menopause (the end of the menstrual cycle) occurs is about 50. Decreased estrogen leads to thinning of the vaginal walls, shrinking of the vagina and labia majora, and decreased vaginal lubrication. These conditions can be severe enough to cause the woman pain during intercourse. Women who were sexually active either through intercourse or through masturbation before menopause and who continue sexual activity after menopause are less likely to experience vaginal problems. Women can use hormone-replacement therapy or hormone-containing creams to help maintain vaginal health. In men, testosterone production declines over the years, and the testes become smaller. The volume and force of ejaculation decrease and sperm count is reduced, but viable sperm may still be produced in elderly men. Erection takes longer to attain, and the time after orgasm during which erection cannot occur (the refractory period) increases. Medications and vascular disease, diabetes, and other medical conditions can cause erectile dysfunction.

IV

Physiology of Sex

Understanding the processes and underlying mechanisms of sexual arousal and orgasm is important to help people become more familiar with their bodies and their sexual responses and to assist in the diagnosis and treatment of sexual dysfunctions. Nevertheless, it was not until the work of American gynecologist William H. Masters and American psychologist Virginia Johnson that detailed laboratory studies were conducted on the physiological aspects of sexual arousal and orgasm in a large number of men and women. Based on data from 312 men and 382 women and observations from more than 10,000 cycles of sexual arousal and orgasm, Masters and Johnson described the human sexual response cycle in four stages: excitement, plateau, orgasm, and resolution.

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In men who are unaroused, the penis is relaxed, or flaccid. In unaroused women, the labia majora lie close to each other, the labia minora are usually folded over the vaginal opening, and the walls of the vagina lie against each other like an uninflated balloon.

A

Excitement

The excitement stage of sexual arousal is characterized by increased blood flow to blood vessels (vasocongestion), which causes tissues to swell. In men, the tissues in the penis become engorged with blood, causing the penis to become larger and erect. The skin of the scrotum thickens, tension increases in the scrotal sac, and the scrotum is pulled up closer to the body. Men may also experience nipple erection.

In women, vasocongestion occurs in the tissue surrounding the vagina, causing fluids to seep through the vaginal walls to produce vaginal lubrication. In a process similar to male erection, the glans of the clitoris becomes larger and harder than usual. Muscular contraction around the nipples causes them to become erect. However, as the excitement phase continues, vasocongestion causes the breasts to enlarge slightly so that sometimes the nipples may not appear erect. Vasocongestion also causes the labia majora to flatten and spread apart somewhat and the labia minora to swell and open. The upper two-thirds of the vagina expands in a “ballooning” response in which the cervix and the uterus pull up, helping to accommodate the penis during sexual intercourse.

Both women and men may develop “sex flush” during this or later stages of the sexual response cycle, although this reaction appears to be more common among women. Sex flush usually starts on the upper abdomen and spreads to the chest, resembling measles. In addition, pulse rate and blood pressure increase during the excitement phase.

B

Plateau

During the plateau stage, vasocongestion peaks and the processes begun in the excitement stage continue until sufficient tension is built up for orgasm to occur. Breathing rate, pulse rate, and blood pressure increase. The man's penis becomes completely erect and the glans swells. Fluid secreted from the Cowper's gland (located near the urethra, below the prostate) may appear at the tip of the penis. This fluid, which nourishes the sperm, may contain active sperm capable of impregnating a woman. In women, the breasts continue to swell, the lower third of the vagina swells, creating what is called the orgasmic platform, the clitoris retracts into the body, and the uterus enlarges. As the woman approaches orgasm, the labia majora darken.

C

Orgasm

Orgasm, or climax, is an intense and usually pleasurable sensation that occurs at the peak of sexual arousal and is followed by a drop in sexual tension. Not all sexual arousal leads to orgasm, and individuals require different conditions and different types and amounts of stimulation in order to have an orgasm. Orgasm consists of a series of rhythmic contractions in the genital region and pelvic organs. Breathing rate, pulse rate, and blood pressure increase dramatically during orgasm. General muscle contraction may lead to facial contortions and contractions of muscles in the extremities, back, and buttocks.

In men, orgasm occurs in two stages. First, the vas deferens, seminal vesicles, and prostate contract, sending seminal fluid to the bulb at the base of the urethra, and the man feels a sensation of ejaculatory inevitability—a feeling that ejaculation is just about to happen and cannot be stopped. Second, the urethral bulb and penis contract rhythmically, expelling the semen—a process called ejaculation. For most adult men, orgasm and ejaculation are closely linked, but some men experience orgasm separately from ejaculation.

In women, orgasm is characterized by a series of rhythmic muscular contractions of the orgasmic platform and uterus. These contractions can range in number and intensity. The sensation is very intense—more intense than the tingling or pleasure that accompany strong sexual arousal.

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