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Postby bklynite » Mon May 15, 2017 11:01 am

Why is the answer A over B? If a person had a deficient LH receptors, wouldn't you want to use NPY to increase the LH levels (similar to how we give insulin to people with type II diabetes)
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Re: AAMC FL2 BB 35

Postby NS_Tutor_Andrew » Mon May 15, 2017 12:47 pm

Hi bklynite,

Excellent question -- I think the key to resolving it would be to pay careful attention to how the specific receptors fit into the causal chain here. GnRH receptors are expressed in the APG cells, and allow APG cells to respond to GnRH and produce LH. LH receptors, in contrast, are found primarily in the cells of the ovary/testis & allow those cells to respond to LH, which is not what the question is interested in. So, to draw out the chain here more carefully:

1. GnRH --> interacts with APG cells via GnRH receptors
2. APG cells --> produce LH
3. LH --> interacts with target cells via LH receptors

Another way of saying this is that GnRH receptors are, in a sense, what allow APG cells to produce LH.

Therefore, if an individual has deficient GnRH receptors, ramping up the amount of GnRH present in the blood via NPY would help overcome that deficiency and allow sufficient LH to be produced. The parallel with diabetes is interesting, but may be more confusing than helpful here. The closer parallel would be with early stages of insulin resistance; at first, as insulin receptors lose sensitivity in cells, the body's response is to produce more insulin. The idea is essentially "OK, if the receptors are less sensitive, let's compensate for it in a brute-force way but ramping up levels of substrate." The progression from insulin resistance to out-and-out type 2 diabetes is what happens when that strategy stops working. (This is a simplified version of the pathogenesis of type 2 DM for sure, but...). Anyway, that's the strategy they're talking about in this question. But that's kind of a digression, I think the key point is recognizing how the receptors fit into this sequence of events.

Hope this is helpful!
Andrew D.
Content Manager, Next Step Test Prep.

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