Summary of female reproductive cycle days 1-28

■ The first five days of the cycle include the menstrual phase. ■ Progesterone and estrogen levels are low. ■ Menses occurs. ■ GnRH pulses more frequently promoting FSH and LH levels to rise. ■ Primary follicles are stimulated to develop. ■ Days five through thirteen consist of the preovulatory ovarian phase and the proliferative uterine phase. • Simultaneously, the production of estrogen increases, stimulating further follicular maturation. • Endometrial cells proliferate, thereby doubling the thickness of the endometrium. ■ Rising estrogen levels stimulate increased pulsing of GnRH and increased secretion of FSH and LH (positive feedback loop with estrogen). ■ Primary oocyte undergoes meiosis to form secondary oocyte. • Estrogen levels peak causing an LH surge. ■ LH stimulates the mature follicle to rupture and release the secondary oocyte. • Days 15-28 include the postovulatory ovarian phase and the secretory uterine phase. ■ The collapsed follicle becomes the corpus luteum, secreting greater amounts of progesterone, estrogen, and inhibin. ■ increased ovarian hormones, especially progesterone, promote endometrial proliferation and secretion. • Endometrial glands secrete glycogen preparing for implantation of an embryo. • Higher levels of inhibin stop the formation of LH and FSH by the anterior pituitary. • If the secondary oocyte is not fertilized, the corpus luteum degenerates and cycle begins again.

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