Estrogens are metabolized by the liver and secreted in bile where some is reabsorbed back into the body. Metabolites of estridiol are excreted in the urine. Estrogens in the blood stream inhibit the release of FSH and LH, in some circumstances, via negative feedback. At other times, as in the preovulatory LH surge, estrogens increase the release of LH, via positive feedback. Estrogen also increases the excitability of uterine smooth muscle , myometrial sensitivity to oxytocin and increases the libido in women by a direct action on hypothalamic neurons.
Progesterone has the principal targets of the uterus , breasts and the brain.
It promotes the development of breast tissue, causes changes in the endometrial lining during the luteal phase of the cycle, decreases the excitability of myometrial cells and decreases uterine sensitivity to oxytocin. Cells of the developing follicle also produce the polypeptide hormone inhibin which inhibits FSH secretion by a direct action on the pituitary. The pineal gland can be found deep in the brain at the top of the third ventricle where it is is close communication with the cerebrospinal fluid. In the adult, the pineal gland can often be seen in x-rays of the brain because of the accumulation of radiopaque calcium phosphate and carbonate into small granules called pineal sand. This diurnal variation is controlled by norepinephrine from sympathtic nevous input that is regulated by the light-dark cycle in the environment.