Nothing seems as powerful for good or evil as women’s hormones. We hear that hormones give women that special glow when pregnant (they do!). We also hear that hormones cause the PMSing woman to freak out, the postpartum woman to weep out, and the menopausal woman to witch out (they don’t!). My book, The Hormone Myth debunks this idea of the “hormonal woman.”

Everybody talks about them, but what exactly are hormones? What they do is nothing short of miraculous—they orchestrate a complex symphony of biological mechanisms. In general, hormones are the chemicals produced by the body that send messages to organs to help regulate biological processes. Reproductive hormones in particular work to regulate reproductive functioning like menstruation, pregnancy, and menopause. The primary female reproductive hormones are follicle stimulating hormone (FSH), luteinizing hormone (LH), estrogen, progesterone, and human chorionic gonadotropin (HCG). Here’s a brief lesson on how each of them work:

Follicle Stimulating Hormone (FSH)

FSH is secreted by the pituitary gland in the brain. Each month, it stimulates the growth of a follicle that produces an egg in the ovary.

Luteinizing Hormone (LH)

LH is also secreted by the pituitary gland. It plays a part in the menstrual cycle by causing the production of estrogen in the ovary, and the release of the mature egg from the follicle.

Estrogen

Estrogen is produced by several parts of the body: the ovaries, the adrenal glands, fatty tissue, and the placenta during pregnancy. In puberty, it regulates the development of secondary sex characteristics like breasts and pubic hair. In menstruation, estrogen facilitates the growth of the uterine lining. Estrogen helps to maintain the lining during pregnancy, and plays an important role in the development of the fetus.

Progesterone

Progesterone is secreted by the empty follicle that released the egg. It also helps to build up the lining of the uterus. In the first trimester of pregnancy, this hormone rises dramatically. It keeps the muscles of the uterus relaxed, and is instrumental in keeping the mother’s immune system from rejecting the foreign DNA, also known as: the baby.

Human Chorionic Gonadotropin (HCG)

HCG is the critical hormone produced during pregnancy. It is made by what eventually becomes the placenta and it stops monthly egg production. It also helps to increase levels of estrogen and progesterone in the first ten weeks of pregnancy. At-home pregnancy tests work by detecting the presence of this hormone.

During the month, if no implantation of an egg occurs, the higher levels of progesterone and estrogen cause a decrease in the production of LH and FSH, which in turn decrease progesterone and estrogen. This makes the blood vessels in the uterus constrict, decreasing the supply of nutrients to the lining. Prostaglandins, which are chemicals made by the uterine lining, cause the uterus to contract (here come the cramps!) and the lining is shed in the menstrual flow. In the years leading up to menopause, the levels of estrogen and progesterone start to fluctuate more dramatically during the monthly cycle, and then start to gradually decline, eventually becoming too low to maintain the menstrual cycle.

And there you have it. Hormones keep our reproductive parts humming, and make pregnancy possible until we get to menopause. They can cause physical symptoms like cramps and bloating with menstruation, or hot flashes during menopause. And yes, those symptoms can affect your mood. But not to the degree that your functioning is threatened. And that is the lie of the hormone myth—that fluctuating hormones make women irrational and unreliable. And that’s a bad rap that women (and hormones) don’t deserve.

To learn more about the hormone myth, read my book The Hormone Myth: How Junk Science, Gender Politics, and Lies About PMS Keep Women Down, available at booksellers everywhere.