Menopause occurs naturally when a woman's ovaries run out of functioning eggs. At the time of birth, most females have about 1 to 3 million eggs, which are gradually lost throughout a woman's life. By the time of a girl's first menstrual period, she has an average of about 400,000 eggs. By the time of menopause, a woman may have fewer than 10,000 eggs. A small percentage of these eggs are lost through normal ovulation (the monthly cycle). Most eggs die off through a process called atresia.
Normally, FSH, or follicle-stimulating hormone (a reproductive hormone), is the substance responsible for the growth of ovarian follicles (eggs) during the first half of a woman's menstrual cycle. As menopause approaches, the remaining eggs become more resistant to FSH, and the ovaries dramatically reduce their production of a hormone called estrogen.
Estrogen affects many parts of the body, including the blood vessels, heart, bone, breasts, uterus, urinary system, skin, and brain. Loss of estrogen is believed to be the cause of many of the symptoms associated with menopause. At the time of menopause, the ovaries also decrease their production of testosterone -- a hormone involved with sex drive.
Menopause simply means the end of menstruation for one year. As a woman ages, there is a gradual decline in the function of her ovaries and the production of estrogen. Around the time a woman turns 40, this process speeds up. This transition is known as perimenopause.
Women typically menstruate for the last time at about 50 years of age. A few stop menstruating as young as 40, and a very small percentage as late as 60. Women who smoke tend to go through menopause a few years earlier than nonsmokers...