Hormones in diagram:  follicle stimulating hormone, leutenizing hormone, estrogen, progesterone

A   B                                   C  D                                E                 ?

 

 

A.  Beginning of menstrual bleeding (sloughing uterine lining)

FSH level increases

FSH stimulate follicle development

 

B.  Follicle begins secreting estrogen

Estrogen causes growth of uterine lining (more cells)

Estrogen increasing causes negative feedback to FSH (FSH level decreases)

 

C.  Estrogen level peaks

Estrogen causes positive feedback to LH & FSH

 

D.  FSH & LH spike

FSH spikes causing weakening of follicle wall

LH spikes causes rupture of follicle wall

LH causes follicle to change form into "corpus luteum"

Corpus luteum produces increasing progesterone

Progesterone stimulates vessel fomation & glycogen storage in uterine wall

[Corpus luteum also produces gradually increasing estrogen]

Rising estrogen depresses FSH (so new follicles do not develop)

 

E.  Egg not fertilized; no embryo

Embryo does not send HCG signal

[If embryo implants, then corpus luteum continues producing progesterone and estrogen to maintain tissue and vascularization of uterus to support fetal growth]

Corpus luteum degenerates

Progesterone falls

Estrogen falls

Pituitary no longer inhibited (restrained)

Pituitary LH & FSH escape inhibition and begin increasing

 

E.  if Egg IS fertilized

Embryo produces HCG

HCG signals corpus luteum to continue producing high levels of E & P

Corpus luteum does NOT degenerate

Progesterone level stay high

Estrogen level stays high

Pituitary remains inhibited and LH & FSH level stay very low

 

?.  Beginning of menstrual bleeding...