The term menopause means literally "pause in the menses" and refers to the cessation of ovarian activity and menstruation that occurs at about the age of 50. During the postmenopausal years, which account for about a third of a woman's life span, the ovaries are depleted of follicles and stop secreting estradiol and inhibin. The fall in estradiol is due to changes in the ovaries, not in the pituitary; indeed, FSH and LH secretion by the pituitary is elevated because of a lack of negative feedback from estradiol and inhibin.
The only estrogen found in the blood of postmenopausal women is the weak estrogen estrone, formed by the mesenchy-mal cells in adipose tissue. Estrone is formed from weak andro-gens, such as androstenedione and dehydroepiandrosterone (DHEA), secreted from the adrenal cortex. Since adipose tissue is the only source of estrogen, postmenopausal women who have more adipose tissue have higher levels of estrogen and less propensity toward osteoporosis.
Clinical Investigation Clues
Remember that Gloria stated that she was not taking birth control pills.
If she were taking birth control pills, how could they be used to prevent periods?
Days from LH peak Cycle day
■ Figure 20.38 Changes in basal body temperature during the menstrual cycle. Such changes can be used in the rhythm method of birth control.
It is the withdrawal of estradiol secretion from the ovaries that is most responsible for the many symptoms of menopause. These include vasomotor disturbances and urogenital atrophy. Vasomotor disturbances produce the "hot flashes" of menopause, where a fall in core body temperature is followed by feelings of heat and profuse perspiration. Atrophy of the urethra, vaginal wall, and vaginal glands occurs, with loss of lubrication. There is also increased risk of atherosclerotic cardiovascular disease and increased progression of osteoporosis (chapter 19).
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