The function of ovaries that commonly reaches its peak at the age of 30 begin to decline gradually afterwards. But in fact, serious problems don’t usually occur before the age of 40. The reason of such decline is decreasing ability of the aging ovaries to respond to pituitary gonadotropins. Secretion of estrogens reduces in spite of the fact that these gonadotropins (that are partially released from the negative-feedback inhibition by estrogen) are secreted in greater amounts. As a result, menstrual periods and ovulation first become irregular and eventually stop completely.
Some secretion of estrogen usually continues beyond these events but subsequently reduces until it is inadequate to maintain the estrogen-dependent tissues: the breasts and genital organs gradually atrophy; the decrease in protein anabolism causes thinning of the skin and bones; however, sexual drive is often no reduced but may be even increased. Severe emotional strains and disturbances are common during menopause and are generally ascribed not to a direct effect of estrogen deficiency but to the disturbing nature of the entire period — the awareness that reproductive potential is ended, the hot flashes, etc. Hot flashes are very typical of menopause. They result from dilation of the skin arterioles, causing a feeling of warmth and marked sweating; why estrogen deficiency causes this is unknown. Many of these menopause symptoms can be smoothed by the additional use of certain amount of estrogen.
One more important aspect of menopause is the relationship between estrogen and plasma cholesterol. Estrogen considerably reduces the level of the plasma cholesterol, and this or some related effect on lipid metabolism may explain why women have much less arteriosclerosis than men until after the menopause, when the incidence becomes similar in both sexes.
Changes in aging males are significantly less radical. Once testosterone and pituitary gonadotropin secretions are initiated at puberty, they continue throughout adult life. A steady decrease in testosterone secretion in later decades apparently reflects slow deterioration of testicular function. The mirror-image rise in gonadotropin secretion is due to diminishing negative-feedback inhibition from the decreasing plasma testosterone concentration. In spite of the significant decrease, testosterone secretion is preserved in the majority of men to maintain sexual vigor throughout life, and fertility has been documented in men even in their eighties. So, there is generally no complete stop of reproductive function similar to female menopause.