IB Biology-Menstrual Cycle

Stage 1 of follicular phase

FSH secreted from the anterior pituitary stimulates the growth of ovarian follicles

Stage 2 of follicular phase

The dominant follicle produces estrogen which inhibits the secretion of FSH (neg feedback) so that no new follicles can form.

Stage 3 of the follicular phase

estrogen acts on the uterus to stimulate the thickening of the endometrial layer

Stage 1 of ovulation

halfway through the cycle, estrogen stimulates the anterior pituitary to secrete other hormones (pos feedback)

Stage 2 of ovulation

this positive feedback causes: LH is stimulated in large surges and FSH is stimulated in lesser surges

Stage 3 of ovulation

LH causes the dominant follicle to rupture and release an egg (secondary oocyte). This is ovulation

Stage 1 of the luteal phase

the ruptured follicle develops into a slowly degenerating corpus luteum

Stage 2 of the luteal phase

the corpus luteum secretes high levels of progesterone and lesser levels of estrogen

Stage 3 of the luteal phase

estrogen and progesterone act on the uterus to thicken the endometrial lining (prep for pregnancy)

Stage 4 of the luteal phase

estrogen and progesterone also inhibit secretion of FSH and LH, preventing any follicles from developing.

Stage 1 of menstruation

if fertilization occurs, the developing embryo will implant into the endometrium and release hormones to sustain the corpus luteum.

Stage 2 of menstruation

if fertilization doesn't occur, the corpus luteum eventually degenerates

Stage 3 of menstruation

when the corpus luteum degenerates, estrogen and progesterone levels drop and the endometrium can no longer be maintained

Stage 4 of menstruation

endometrial layer is sloughed away and released as menstrual blood

Stage 5 of menstruation

estrogen and progesterone levels are too low to inhibit anterior pituitary, so the cycle restarts.