Reproductive hormones in females

▪ FSH stimulates development of egg cells, called ova, which develop in structures called follicles. Follicle cells produce the hormone inhibin, which inhibits FSH production. Follicles also produce estradiol and progesterone.

▪ LH also plays a role in the development of ova, induction of ovulation, and stimulation of estradiol (a form of estrogen) and progesterone production by the ovaries.

▪ Estrogens (such as estradiol) and progesterone are released from the developing follicles. Estrogen is the reproductive hormone in females that assists in endometrial regrowth, ovulation, and calcium absorption; it is also responsible for the secondary sexual characteristics of females such as breast development, flaring of the hips, and a shorter period necessary for bone maturation. Progesterone assists in endometrial re-growth and inhibition of FSH and LH release.

▪  These hormones together regulate the ovarian and estral cycles. The ovarian cycle governs the preparation of endocrine tissues and release of eggs, while the estral cycle governs the preparation and maintenance of the uterine lining. These cycles occur concurrently and are coordinated over a 21-24 (bovine) day cycle.

▪  Slowly rising levels of FSH and LH cause the growth of follicles on the surface of the ovary. This process prepares the egg for ovulation.

▪ As the follicles grow, they begin releasing estrogens and a low level of progesterone.

▪  Progesterone maintains the endometrium to help ensure pregnancy if the egg is fertilized. The trip through the fallopian tube takes about seven days.

▪ If pregnancy implantation does not occur, the lining is sloughed off. After about five days, estrogen levels rise and the estral cycle enters the proliferative phase.

▪ The endometrium begins to regrow, replacing the blood vessels and glands that deteriorated during the end of the last cycle.