Phases of the Female Reproductive Cycle - Hormonal regulation

FSH, LH and estrogen • FSH travels through the bloodstream from the anterior pituitary to the ovaries. • FSH promotes follicular growth. Increased follicular growth promotes estrogen production. • Small increases in blood estrogen levels inhibit the release of FSH and LH into the blood but promote their accumulation in the anterior pituitary. Estrogen and LH • High estrogen levels exert a positive feedback effect on both the hypothalamus and anterior pituitary. • A rush Of LH and FSH is secreted. • The LH surge initiates ovulation (release of the secondary oocyte) and triggers a decline in estroger production by the follicle. LH also transforms the ruptured follicle into a corpus luteum. Estrogen, progesterone and inhibin • The corpus luteum secretes both estrogen and progesterone, increasing their blood levels. • Increased ovarian hormones inhibit the release of LH and FSH. • The release of inhibin from the corpus luteum enhances this inhibitory effect. • As gonadotropin (FSH and LH) levels decline, the corpus luteum begins to degenerate, reducing estrogen and progesterone production. • The sharp decline in ovarian hormones triggers the release of GnRH, LH and FSH and the begins again.

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