Basic Endocrinology

Menopause

Menopause refers to a gradual process that culminates with the cessation of a woman's regular monthly menstrual cycles and reproductive life. Menopause is a natural biological process that is characterized by hot flushes, irregular menstrual cycles, and reduced circulating estrogen and progesterone levels. The number of eggs remaining in the ovaries falls below a level threshold of approximately 1000, the ovaries stop producing these hormones completely and thus no longer release eggs. This most often occurs in women between the ages of 50 and 51, although some women experience menopause in their 30s, 40s, or even 60s. Premature menopause, referred to as premature ovarian failure (POF), occurs when a woman's periods stop before the age of 40 due to the cessation of estrogen production by the ovaries. POF may be caused by genetic abnormalities, viral infections, or production of autoantibodies which inhibit ovarian function. Certain medical procedures, such as chemotherapy and radiation therapy, can damage the ovaries and trigger menopause within a few months of treatment. Surgical removal of the ovaries (oophorectomy) will immediately induce menopause. Animal experiments have shown that many commercial chemicals are toxic to the ovaries and at high concentrations (levels beyond those measured in human tissues in contemporary studies) accelerate the loss of eggs from the ovaries. In contrast, cigarette smoking has been shown to accelerate the age of menopause and to result in the loss of eggs in animal studies. Therefore, there is concern that environmental toxicants can affect ovarian function, accelerate the rate of egg loss and lead to an advance in the age of menopause.

Estrogen and progesterone are female sex hormones that play key roles in uniquely female functions. In particular, these hormones are involved in preparing the female body for pregnancy by stimulating the growth of a thick lining in the uterus where a fertilized egg can grow and develop into a baby. Prior to menopause, the majority of estrogen and progesterone in a woman's body is produced by the ovaries. However, since other organs produce small amounts of these hormones (i.e. adrenal glands, liver, and kidneys), post-menopausal women continue to have low levels of estrogen and progesterone.