Human ovulatory cycle ~28 days in length includes menses ovulation occurs spontaneously cycles occur throughout the year one egg produced / month three phases:

– follicular phase (proliferative, estrogenic)– luteal phase (secretory, progestational)– menstrual phase (destructive)

Menstrual phase

4-5 days in length uterine lining degenerates follicle development continues

– several antral follicles exist– follicles stimulated by LH, FSH pulses– estrogen levels in blood begin to rise

Follicular phase begins on last day of menses phase lasts until ovulation (~day 14) follicles grow, secrete increasing amounts of estrogen during most of this phase, estrogen exerts “negative

feedback” by days 10-12, a few ripe tertiary follicles exist by day 13, 1 Graafian present in uterus, endometrium thickens uterine glands enlarge uterine blood supply increases

Ovulation occurs at end of follicular phase (day 14) triggered by peak in estrogen (days 12-13; “positive

feedback”) estrogen causes GnRH surge, LH surge estrogen also “primes” (sensitizes) pituitary gland to

GnRH FSH surge also occurs LH surge initiates meiosis in oocyte of Graafian follicle

(now a preovulatory follicle) LH also triggers ovulation (9-12 hrs after LH surge peaks) other antral follicles doomed to atresia

Luteal phase last half of menstrual cycle (~14 days) follicle is transformed to corpus luteum (CL) by LH

surge CL secretes progesterone, estradiol high progesterone, estradiol exert negative feedback on

hypothalamus uterine lining becomes thick, spongy LH, FSH levels are negligible > atresia if fertilization takes place and conceptus implants,

placental hCG rescues corpus luteum no hCG > menstrual phase