Five hormones regulate a woman’s menstrual cycle gonadotropin releasing hormones GnRH . follicle stimulating hormone FSH., luteinizing hormone LH . estrogens and progesterone. These hormones form a hierarchy of control . GnRH is synthesized in the hypothalamus and controls the release of both fsh and lh from the anterior pituitary gland where they are produced. Fsh causes the ovarian follicle and its egg to mature and the mature follicle synthesizes and releases estrogens LH stimulates conversion of a ruptures follicle into another gland the corpus luteum. Which synthesizes and releases both estrogen and progesterone. The presence of progesterone in the blood inhibits release of GNRH from the hypothalamus. And so inhibits release of both fsh and lh.

After ovulation the anterior pituitary gland stops producing fsh but continue to release lh. Which causes conversion of the ruptured follicle into a corpus luteum. The estrogen and progesterone released from the corpus luteum act together to prepare the reproductive organs for pregnancy and stimulate the endometrium to become soft , moist and thick. Progesterone increased the volume of muscle and blood vessels in the walls of the uterus stimulated activity of mucous glands in the endometrium and causes mild gland to develop the breasts.

In the absence of pregnancy the corpus luteum degenerates as the cycle nears 28 days in length and the estrogen and progesterone levels decreases. Without hormones support to the endometrium the arteries in this area constrict and tissues are deprived of nutrients and flow off. Menstruation occur marking the end of the one menstrual cycle and beginning of another.