The Biology Of Menopause - What Is Menopause: Menopause Managing The Change Of Life

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The biology of menopause

When you are born, your ovaries hold one million to two million egg-containing follicles. But over time, the number declines steadily as you ovulate or the follicles simply disintegrate. When the follicle supply is depleted, your ovaries stop making estrogen and progesterone, the hormones that have regulated your periods through the years. During the time preceding menopause, ovulation and estrogen production become erratic, causing periods to become irregular.

You might think of estrogen as a female hormone because of its important role in menstruation and reproduction. However, its effects are by no means limited to the reproductive system. Estrogen receptors — proteins that estrogen molecules link up with to exert its effects — are found in cells of the liver, digestive system, urinary tract, blood vessels, bones, skin, and central nervous system. When estrogen links to these receptors, it stimulates the cells to produce proteins that help maintain the healthy functions of these tissues and organs. In this way, estrogen has a role in determining the composition of lipids in the blood, the density of bones, the regulation of body temperature, the ability to recall information from memory, and the elasticity of skin and arteries.

Follicle-stimulating hormone (FSH) is the brain hormone that triggers estrogen production in the ovaries during the childbearing years. When estrogen levels drop, FSH rises, trying to stimulate your ovaries to produce more estrogen and maintain your menstrual cycle (see Figure 1). High FSH levels may indicate that the menopausal transition has begun.

Eventually, your periods stop for good. The postmenopausal years begin at menopause, a year after your last period, and last for the rest of your life. This time of life is more than just a postscript to the cessation of menstruation. This is a time when women must pay close attention to the development of such chronic illnesses as osteoporosis, heart disease, and cancer. If you haven't already taken up healthy habits — exercising, eating well, avoiding smoking, and reducing stress — doing so now can help ensure good health during the postmenopausal years (see "Menopause and healthy living").

Figure 1: Monthly hormone cycle During a woman's reproductive years, her hormones follow a regular monthly pattern. Follicle-stimulating hormone (FSH) stimulates the growth of a fluid-filled follicle containing an egg. Luteinizing hormone (LH) tells the ovary to produce more estrogen to spur the release of an egg. After the egg erupts from the follicle (ovulation), the follicle remnant, known as the corpus luteum, produces progesterone, which stimulates the growth of the endometrium (lining of the uterus) to receive and nourish a fertilized egg. Meanwhile, FSH and LH levels drop and, if no fertilized egg reaches the endometrium, the cycle repeats itself the next month.

Last updated:	August 13, 2007