13.8: Age Changes in the Female System

Aging of the female reproductive system can be divided into two phases, which are separated from each other by menopause. Menopause is the time when age changes in the ovaries cause menstrual cycles to cease for at least 1 year. The average age at which menopause occurs is 51, though it can occur any time between ages 45 and 55. Women who have not experienced menopause are called premenopausal, and those who have passed through it are called postmenopausal.

Women lose reproductive ability quickly during menopause. Female animals do not have menopause. Animals lose their ability to reproduce very gradually as they age, though there may be a few animals that have menopause (e.g., whales). Scientists speculate about why menopause occurs in humans and in essentially no other animals. One explanation rests on the great amount and length of care human infants require after they are born. Evolution by natural selection promotes menopause because it allows women to nurture children more effectively. Bearing more children at advanced ages would prevent women from devoting enough time and energy to nurture the children they already had. Women passed menopause could also help raise children from other women.

Menopause is important for two reasons. First, pregnancy, and therefore reproduction, is no longer possible because ovulation has stopped. Second, bodily structures and functions that are influenced by estrogen and progesterone undergo significant changes after menopause because blood levels of these hormones drop and stay low when follicles no longer mature. Some of these hormone-related age changes were described in Chaps. 4 and 9 (e.g., changes in blood lipoproteins, skeletal changes). These and other postmenopausal changes are also described in Chapter 14. This chapter will discuss premenopausal, menopausal, and postmenopausal age changes in the reproductive system.

Ovaries

Before menopause, as more follicles ovulate or become atretic, the number of follicles capable of ovulation decreases, and by age 50 almost no viable follicles remain. While the number of viable follicles is decreasing, the follicles that develop during each ovarian cycle develop less completely, fewer of them ovulate and form a corpus luteum, and therefore less estrogen and progesterone are produced. Eventually no follicles mature fully, ovulation ceases, ovarian cycles disappear, and reproduction becomes impossible. Since the occurrence of menstrual cycles depends on the hormones produced by ovarian cycles, menstrual cycles also cease and menopause occurs.

After menopause, the ovaries produce very small quantities of estrogen and progesterone, and this production gradually diminishes. These hormonal changes are responsible for many other changes, including most age changes in other parts of the reproductive system.

Oviducts

In spite of age changes, the oviducts do not entirely lose the ability to carry ova and sperm cells. Of course, this point is moot once ovulation ceases.

Uterus

The most noticeable change in the uterus before menopause is a decrease in the degree of endometrial thickening during menstrual cycles. Since this decline is due to reduced ovarian hormone production, this change is observed most frequently during menstrual cycles that accompany ovarian cycles with no ovulation.

The menstrual flow resulting from cycles that have reduced endometrial thickening may be so slight that it is not viewed as constituting a true menstrual period. Menstrual cycles may seem to become very long because two or more cycles may occur before enough menstrual flow is produced to definitively mark the end of a cycle.

As the proportion of ovarian cycles involving no ovulation increases, the time between menstrual periods also increases. When no periods happen for 1 year, menopause has occurred. Note that occasional periods may occur after menopause. However, pregnancy becomes impossible when ovulation ends or when the endometrium fails to thicken enough to form a placenta capable of supporting the development of an embryo.

Both before and after menopause, the uterus often tips backward and settles lower in the abdominal cavity as its supporting ligaments weaken and surrounding structures shift. If the lowering of the uterus is excessive, it may descend into or through the vagina. This abnormal condition is called uterine prolapse. Uterine prolapse may also develop as a complication from childbirth or from surgery in the pelvic area.

After menopause, the entire uterus shrinks. It may decrease in size by 50 percent within 15 years after menopause and may eventually shrink to less than 2.0 cm in width.

Vagina

Age changes have no significant effect on the reproductive functions of the vagina. However, they significantly reduce its role as a barrier against abrasion and microbes because as the vagina becomes smaller, thinner, and less elastic, it is more easily damaged by even mild physical trauma, such as friction during sexual intercourse. The increased risk of injury and the decline in lubrication are also more likely to result in pain from sexual intercourse. As the risk of vaginal injury rises, so does the risk of developing sores and vaginal infections. The risk of vaginal infections rises also because as age increases, the lining cells contain and release less glycogen. As glycogen declines, less acidic material is produced by healthful microbes and injurious microbes can flourish.

Finally, since the urethra lies immediately in front of the vagina, thinning of the vaginal wall increases the frequency of urethral and bladder irritation and inflammation (cystitis) from agitation of the vagina during intercourse. Painful urination and temporary urinary incontinence may result.

The rate of age changes in the vagina can be slowed by continued frequent sexual intercourse and by administered estrogen. Therefore, the undesirable consequences of these changes can be minimized. Topical application of estrogen-containing creams directly to the vagina is especially effective. In addition, because the postmenopausal vagina is relatively thin, much of the estrogen enters the blood and can have beneficial effects in other areas.

External Structures (Genitalia)

Though the changes in the vagina are the main reasons for the increased risk of developing vaginal infections, age-related shrinkage of the labia majora may also play a contributing role. This shrinkage causes the labia to remain separated more of the time, allowing microbes to enter the vagina more easily. Other age changes in the external genitalia are discussed in connection with age changes in female sexual activity, below.

Breasts

Age changes in the breasts result primarily from the decline in ovarian hormones after menopause. Shrinkage of glandular material, increases in fat, and weakening of fibrous materials in the breasts reduce their firmness and support, causing them to sag and droop rather than protrude from the chest (Figure 13.13). Breasts that have stretched fibers from years with little support from undergarments may show more sagging. These changes have significant cosmetic effects. Other age changes in the breasts are discussed in connection with female sexual activity.