Progesterone, << proh JEHS tuh rohn, >> is a hormone produced mainly by the ovaries and the placenta in female animals during the period when they are able to bear young. Small amounts are also produced by the adrenal glands in both females and males and by the testes in males.
Progesterone plays an important role in preparing a woman’s uterus for pregnancy. About midway through a woman’s monthly menstrual cycle, one of her two ovaries releases an egg. This process, called ovulation, causes changes in the ovary so that it releases high levels of progesterone into the blood for 10 to 12 days. Progesterone stimulates the lining of the uterus so that the egg, if it has been fertilized, may attach to the uterine wall. If pregnancy does not occur, the ovary stops producing high levels of progesterone. The uterine lining then breaks down and passes out of the body during menstruation. See Menstruation .
The monthly increase of progesterone in a woman’s blood after ovulation causes cyclic changes in other body functions. For example, the woman’s body temperature increases, and her breasts may enlarge or become especially sensitive. During pregnancy, the placenta produces large amounts of progesterone. The high progesterone level keeps the uterine muscle relaxed so the baby is not born too soon. See Placenta .
Physicians use progesterone as a drug to treat disorders of the reproductive system. These disorders include premenstrual tension and irregular menstruation. Synthetic forms of progesterone are used alone and in combination with synthetic estrogens in birth control pills.
