Mechanism behind the LH Surge

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So we all know that low levels of estrogen induces negative feedback on the hypothalamus pituitary axis for gonadotrophin production and that after a certain critical level, positive feedback occurs which leads to the LH surge.

Im just curious on how this switch can occur. I cant really think of a way in which the signal cascade can entirely change based on the ligand concentration. Maybe im missing something.

 

[AndyRSC]

I've read two takes on this. The first, supported by FA and Ross Histology states that during ovulation estrogen upregulates GnRH receptors on the anterior pituitary, which causes more LH/FSH, which cause more estrogen, completing the positive feed back circuit. A different take, supported by physio text and contemporary research, is that high levels of estrogen in the late follicular phase cause a GnRH surge from the hypothalamus itself. How that happens is fairly complex and not fully understood, and is almost certainly beyond the scope of Step I. You can find out more here.

 

[alternatego]

pretty cool post dude, thanks