The ovaries are located in the pelvic cavity, one on each side of the uterus. The hormones produced by the ovaries are the steroids estrogen and progesterone, and the protein inhibin.
Estrogen is secreted by the follicle cells of the ovary; secretion is stimulated by FSH from the anterior pitu-itary gland. Estrogen promotes the maturation of the ovum in the ovarian follicle and stimulates the growth of blood vessels in the endometrium (lining) of the uterus in preparation for a possible fertilized egg.
The secondary sex characteristics in women also develop in response to estrogen. These include growth of the duct system of the mammary glands, growth of the uterus, and the deposition of fat subcu-taneously in the hips and thighs. The closure of the epiphyseal discs in long bones is brought about by estrogen, and growth in height stops. Estrogen is also believed to lower blood levels of cholesterol and tri-glycerides. For women before the age of menopause this is beneficial in that it decreases the risk of athero-sclerosis and coronary artery disease.
Research suggests that estrogen no longer be con-sidered only a “female” hormone. Estrogen seems to have effects on many organs, including the brain, the heart, and blood vessels. In the brain, testosterone from the testes or the adrenal cortex can be converted to estrogen, which may be important for memory, especially for older people. Estrogen seems to have non-reproductive functions in both men and women, although we cannot yet be as specific as we can be with the reproductive functions in women, mentioned previously.
When a mature ovarian follicle releases an ovum, the follicle becomes the corpus luteum and begins to secrete progesterone in addition to estrogen. This is stimulated by LH from the anterior pituitary gland.
Progesterone promotes the storage of glycogen and the further growth of blood vessels in the endo-metrium, which thus becomes a potential placenta. The secretory cells of the mammary glands also develop under the influence of progesterone.
Both progesterone and estrogen are secreted by the placenta during pregnancy.
The corpus luteum secretes another hormone, called inhibin. Inhibin helps decrease the secretion of FSH by the anterior pituitary gland, and GnRH by the hypothalamus.