Ok so i REALLY REALLY need help on the menstraul cycle and the stages I finally get the follicular phase, ovulation, and corpus luteum but i dont understand how the hormones play into the whole scheme. Can someone PLEASE like list each phase with the hormone and what happens pleas please please....this crap kills me
during the ovarian follicular phase (days 5-14), there are low levels of FSH and LH. During this time, LH, from the anterior pituitary causes the release of estradiol from the ovarian follicle. pretty much this whole time, estradiol, which i will abbreviate E2, works to inhibit LH secretion by negative feedback on the hypothalamus and the pituitary. regardless, ideal levels of E2 are secreted.
Like a day or 2 before day 14, there is a dramatic change in the menstrual cycle. E2 no longer works to negatively inhibit LH -- instead, it works in a positive feedback fashion to stimulate LH secretion exponentially. So, in a matter of a day or so, you get a quick spike of LH due to the positive feedback effect of E2 on LH secretion. This is the critical, climactic point in the whole cycle.
At day 14 the follicle turns into the corpus luteum, which now secretes E2, and also lots of progesterone, to get the uterus ready for implantation.
(Here's a technical fact that's good to know, but you won't need to know on the DAT: the newly formed corpus luteum at this point is secreting E2 and progesterone in response to LH. But it only responds to LH because it was E2's job (one of E2's many jobs) prior to the surge to increase LH recpetors on the granulosa cells in the ovarian follicle. Now since the follicle has ruptured, the corpus luteum now can normally, and effectively secrete E2 by responding to LH effectively.)
Days 14-23 or 23, progesterone goes up, and if at day 22 or 23 no implantation occurs, progesterone levels go skyrocketing down and you get menstruation (menses). E2 levels would also plummet.
If at day 22 or 23 you have fertilization, the zygote can get implanted into the uterus, and progesterone and E2 levels stay high.
Days 14-28 is also called the ovarian luteal phase. This is when the corpus luteum is active, hence the name, luteal phase.
Take a look at this chart, it should give a nice summary of what I said:
Now what happens if you go into pregnancy? HCG from the placenta, instead of LH stimulate E2 and progesterone secretion by the corpus luteum. At about day 70 of gestation. HCG levels plummet to rock bottom. However from days 70 to about 280 of gestation, HCS (human chorionic sommatomammotropin) pregnanediol, and estriol levels steadily rise. But after HCG levels fall, then what is there to stimulate estrogen release from the corpus luteum? In other words, where are we going to be getting estrogen from?
It is at day 70 (around 2 months during gestation), that estrogens are no longer coming from the corpus luteum. Now, they are coming directly from the PLACENTA.
cheers
