Sorry if this is a stupid question guys...im just failing to understand how OCPs prevent the estrogen surge thereby preventing LH surge and ovulation? Isin't there estrogen in the OCPs themselves?

I was thinking it can be because there is discrimination between the body's natural estrogen and the synthetic estrogen and so the synthetic estrogen blocks estrogen receptors which increases feedback inhibition on gonadotropins and decreasing the body's natural estrogen and therefore prevents the estrogen surge. I haven't read this anyhwere, its just my reasoning..but if someone knows a definite answer, please post! Thanks for all your help!

anyone?

Actually I think it's more simple than that - OCP gives a staedy low level of oestrogen which is enough to act as neg feedback on LH but not enough to cause the surge -

remember the system has a negative feedback most of the time but just b4 midcylce the increase in oestrogen levels -> switch to positive feedback and hence -> the LH surge and ovulation.

PCO works by a similar mechanism.

Does this help???

maybe this explanation will help you....let's go first with the normal hormone effects: day 1 of menstrual cycle=bleeding; at this point LH will stimulate estrogen production; estrogen is keep increasing in concentration until let's say a concentration X; all the way up until concentration X, estrogen has a negative feedback to LH; when estrogen reaches concentration X, this negative feedbaack 'switch' to a positive feedback and stimulate LH secretion which will give LH surge.....very high levels of LH will give ovulation(breaking of ovarian follicle) and formation of egg and corpus luteum.....from this point corpus luteum starts to secretes progesterone plus some estrogen; from here things get's different if egg will be fecundated or not by a sperm; now, the OCP are most of the time 28 pills....firts 14 pills contain estrogen only to mimic the physiological effect of a normal body but this concentration in blood of estrogen will NEVER reach that concentration X.....as a result LH surge does not happen and ovulation does not occure; the next 14 pills contain mainly progesterone to induce myometrial thickness and to produce menses(i believe the last 3-4 pills have no estrogen or progesterone just like corpus luteum which at the end of lutheal phase stops in production of progesterone because there is no beta hCG from syncitiothrophoblast);

bottom line: OCP mimic normal estrogen and progesterone concentrations seen in a female monthly hormonal cycle EXCEPT the OCP estrogen concentration will NEVER reach that concentration X which could give LH surge=no ovulation....

hopefully it helps.....

thank you Anan and SAAM!! I guess i was looking too much into it, but now this concept is crystal clear! Once again thank you and good luck to you both!

I used to be confused with this too....but i think the simplest explanation is this:
Ovulation happens due to LH surge (not so much as due to estrogen surge)...but giving steady estrogen we inhibit LH by negative feedback. Low LH=no ovulation.
Remember, in the menstrual cycle, the estrogen switches from being negative feedback to positive feedback (by an unknown mechanism) around ovulation. But give steady estrogen externally, u inhibit the process, thereby preventing ovulation.