How Does Menopause Happen?

The ovaries in women contain follicles that hold the egg cells. At birth, there are about 500,000 egg cells. By puberty, only about 75,000 eggs are left. Only about 400 to 500 eggs ever reach maturity and get released during adulthood. The rest degenerate over the years.

During the reproductive years, a gland in the brain generates hormones that cause a new egg to be released from its follicle each month. The follicle then produces the sex hormones estrogen and progesterone, which thicken the lining of the uterus. This enriched lining is prepared to receive and nourish a fertilized egg which could develop into a baby. If fertilization does not occur, estrogen and progesterone levels drop, the lining of the uterus breaks down, and menstruation occurs.

The hormone production in the ovaries begin to decline from the mid-thirties. In the late forties, the process accelerates and hormones fluctuate more, causing irregular menstrual cycles and unpredictable episodes of heavy bleeding. By the early to mid-fifties, periods finally end altogether. However, estrogen production does not completely stop. The ovaries decrease their output significantly, but still may produce a small amount. Also, some estrogen is produced in fat cells with help from the adrenal glands.

Progesterone, the other female hormone, works during the second half of the menstrual cycle to create a lining in the uterus as a viable home for an egg, and to shed the lining if the egg is not fertilized. If you skip a period, it generally means that your body is not making enough progesterone to break down the uterine lining. In contrast, your estrogen levels may remain high even though you are not menstruating.