ok i know i probably shouldn't be so panicky right now but i can't seem to grasp the menstrual cycle... i take the test tomorrow so i know i should probably just let it go, but i feel like i need to know it... can someone give me a basic rundown of which hormone comes in and causes what... the TPR book does not explain the process that well...
All the eggs of a human female are arrested at the primary oocyte stage at the time of birth.
After puberty, a month cycle described below begins.
Each cycle takes about 30 days. Ovulation (release of the secondary oocyte from the ovary occurs on about day 14). By this time meiosis I already took place. Ovulation is caused by an LH surge. LH is a hormone released by the anterior pituitary. LH surge is caused by positive feedback of estrogen. An oocyte is surrounded by zona pollucida (spelling?), which in turn is surrounded by granulosa cells, which in turn are surrounded by theca cells. The growing follicle releases more and more estrogen (quite simply beause it's growing), which after some threshold value exerts positive feedback on the anterior pituitary, resulting in luteal surge (LH surge). LH surge causes ovulation.
The portion of the follicile left over in the overy is called corpus luteum (literally means "yellow body"). Corpus luteum secretes estrogen and progesterone. If no pregnancy occurs, corpus luteum degenerates into corpus albicans (literally means "white body") and the monthly cycle is repeated over.
Pregnacy occurs when the secondary oocyte is fertilized by a sperm. After fertilization occurs, meiosis II takes place.
If pregnancy occurs, placenta forms. It secrtes hCG, which stimulates corpus luteum to secrete estrogen and progesterone. Estrogen prepares the uterine lining for the implantation of the embryo. After about 3 months of pregnancy, corupus luteum degenerates and placenta takes over making estrogen and progesterone. Estrogen and progesterone together exert a negative feedback on the hypothalamus and anterior pituitary. This prevents monthly cycles while a woman is pregnant.
HTH
