LH surge

[mshah]

I am a bit confused on how estrogen during menstruation contributes to an LH surge at the end of the prolif. stage, if LH stimulates androgen to trigger granulosa cells that produce estrogen?

[NS_Tutor_Andrew]

Hi mshah,

Excellent question! So, the shortest answer for our purposes is very simple: don't worry about it for the MCAT. You're not expected to know those molecular mechanisms, although theoretically they could be presented to you in a passage.

The longer answer is that sustained release of estradiol in the follicular phase causes it to start exerting a positive feedback effect on the pituitary gland, resulting in a spike of GnRH that causes the LH surge (a good, and very detailed, source is here). This process seems to also be potentiated by progesterone (see this review]), although that point particularly goes beyond the scope of the MCAT.

A final quick conceptual point to note is that the downstream function of LH doesn't have much direct effect on what causes its release. LH release is triggered by GnRH, so if you're looking for what causes LH release, you have to look 'upstream' to figure out what causes GnRH release.

Hope this helps & best of luck in your study process!