What is Really Going On with Your Hormones?

Last Updated: May 1, 2003

The ovaries contain structures called follicles that hold the egg cells. A baby girl is born with about 2 million egg cells and by puberty there are about 300,000 left. Only about 400 to 500 ever mature fully to be released during the menstrual cycle.

The rest degenerate over the years. During the reproductive years, the pituitary gland in the brain generates hormones that cause a new egg to be released from its follicle each month. The follicle also increases production of 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 following conception. If fertilization does not occur, estrogen and progesterone levels drop, the lining of the uterus breaks down and menstruation occurs.

The ovaries begin to decline in hormone production when a woman is in her mid-30s. In the late 40s, the process accelerates and hormones fluctuate more, causing irregular menstrual cycles and unpredictable episodes of heavy bleeding. By the early to mid-50s, 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, another form of estrogen is produced in fat tissue with help from the adrenal glands (near the kidney). Although this form of estrogen is weaker than that produced by the ovaries, it increases with age and with the amount of fat tissue.

Progesterone, the other female hormone, works during the second half of the menstrual cycle. It creates a lining in the uterus as a viable home for an egg, and sheds the lining if the egg is not fertilized. If you skip a period, your body may not be making enough progesterone to break down the uterine lining. However, your estrogen levels may remain high even though you are not menstruating.

At menopause, hormone levels don’t always decline uniformly. They alternately rise and fall again. These changing ovarian hormone levels affect the other glands in the body, which together make up the endocrine system. The endocrine system controls growth, metabolism and reproduction. This system must constantly readjust itself to work effectively. Ovarian hormones also affect all other tissues, including the breasts, vagina, bones, blood vessels, gastrointestinal tract, urinary tract and skin.

Hormones and change
A woman’s body changes throughout her lifetime. Many of those changes are due to varying hormone levels that happen at different stages in life.

Puberty often starts when a girl is about 12 years old. Her body changes—breasts and pubic hair develop, monthly periods begin.

Menopausal transition, commonly called perimenopause, is the time when a woman’s body is closer to menopause. At this time, a woman’s periods may become less regular, and she may start to feel menopause symptoms, such as hot flashes and night sweats. Perimenopause usually begins about two to four years before the last menstrual period. It lasts for about one year after your last period.

Menopause is marked by a woman’s last menstrual period. You cannot know for sure what is your last period until you have been period-free for one full year.

Postmenopause follows menopause and lasts the rest of your life. Pregnancy is no longer possible. There may be some symptoms, such as vaginal dryness, which may continue long after you have passed through menopause.



Source: The National Institutes of Health

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