The climacteric, or perimenopause, is that phase of the aging process in which a woman passes from reproductive to nonreproductive capability (generally age 45–55 years). The perimenopause normally lasts 4 years and is marked by altered ovarian function (., cycle length increases or decreases and anovulation is more common). Menopause is defined as permanent cessation of menstruation following the characteristic altered ovarian function. The physiology of the climacteric requires a brief review of ovarian physiology. Primordial germ cells migrate to the genital ridge by 5 weeks of gestation. Successive mitotic cellular divisions form oogonia, which in turn give rise. | THE NONREPRODUCTIVE YEARS CLIMACTERIC The climacteric or perimenopause is that phase of the aging process in which a woman passes from reproductive to nonreproduc-tive capability generally age 45-55 years . The perimenopause normally lasts 4 years and is marked by altered ovarian function . cycle length increases or decreases and anovulation is more common . Menopause is defined as permanent cessation of menstruation following the characteristic altered ovarian function. The physiology of the climacteric requires a brief review of ovarian physiology. Primordial germ cells migrate to the genital ridge by 5 weeks of gestation. Successive mitotic cellular divisions form oogonia which in turn give rise to oocytes. Although there are approximately 7 million oogonia present in the fetus at 20 weeks of gestation their numbers gradually decline leaving 2 million at birth and only 300 000 at puberty. This reduction continues until menopause. The oogonia are reduced by atresia the primary cause of loss and ovulation 400-500 per lifetime . As the menopause approaches ovulation is more erratic the ovary becomes less responsive to the gonadotrophic hormones estrogen production is more erratic and often lower and the level of FSH increases. Menopause occurs when the o varies and oocytes response to gonadotropins markedly diminishes or disappears. The average age of menopause in the United States is 49-50 years and it relates to health and genetic background. The age of menopause is not correlated with age at menarche height weight parity or prolonged use of oral contraceptives. Early menopause has been associated with smoking infection chemotherapy especially alkylating agents radiation surgical procedures that impair ovarian blood supply tumors or surgical removal of the ovaries. Early menopause has even been related to left-handedness although menopause is not classified as being premature unless menses cease at 35 y of age. 743 Copyright 2001 The McGraw-Hill Companies. .
