Progesterone

Progesterone is one of two main hormones, the other being estrogen, made by the ovaries of menstruating women. Smaller amounts are secreted by the adrenals. It is the major female reproductive hormone during the latter two weeks of the menstrual cycle. Progesterone is necessary for the survival of the fertilized ovum, the resulting embryo, and the fetus throughout gestation, when production of progesterone is taken over by the placenta.

In the ovaries, progesterone is the precursor of estrogen. Progesterone is also made in smaller amounts by the adrenal glands in both sexes and by the testes in males. It is a precursor of testosterone and of all the important adrenal cortical hormones. Progesterone is made from the sterol pregnenolone, which is in turn made from cholesterol, which is made from acetate, a product of the breakdown of sugar and fat in the body. From progesterone are derived not only the other sex hormones, including the estrogens, but also the corticosteroids, which are essential for stress response, sugar and electrolyte balance, and blood pressure and survival. Because of the role played by progesterone in so many hormones, a deficiency of progesterone can cause a wide range of problems.

The primary task of this hormone is to perform tasks necessary for reproduction. For example, it stimulates the growth of a cushiony endometrial lining that serves as a nest for the fertilized egg, prepares breast tissue for the secretion of breast milk, and generally maintains the advancement of pregnancy. Although progesterone receptors are found mostly in reproductive organs, researchers have also found them in bone and in certain areas of the brain, where their function is still unclear.

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