Bio Questions V1 Passage 8

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Bio Questions V1 Passage 8

Post by vgp1993 » Wed Apr 25, 2018 12:37 pm

This passage made me wonder about whether or not I'm thinking about SNS and PNS responses incorrectly. The passage explains how acetylcholine dilates blood vessels and how they used norepi to constrict blood vessels in the experiment done. I thought that epi and norepi would dilate vessels everywhere except for in the digestive tract in order to get glucose to where it's needed for immediate energy, but the experiment seems to suggest that any broad application of norepi has vasoconstrictive effects.

Could someone help clarify?

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Re: Bio Questions V1 Passage 8

Post by NS_Tutor_Andrew » Thu Apr 26, 2018 1:51 pm

Hi vpg1993,

That's an excellent question. Basically, norepinephrine can act on alpha-receptors to cause vasoconstriction and on beta-receptors to cause vasodilation, so whether it causes vasoconstriction or vasodilation in a given tissue depends on the distribution of receptors (here's a good review). That said, these details probably go beyond what the MCAT usually tests, and if I'm reading the questions associated with that passage correctly, no question actually relies on that knowledge. On one hand, this is a preview of coming attractions in medical school, but on the other hand, it's a useful lesson about how to approach unfamiliar content that shows up in passages -- it's better to have a reaction along the lines of "oh, huh, I guess this is one of those things where there are additional complications if you look super-carefully, as is often the case w/ biology, so I'm going to just roll with it" than "oh no! everything I learned must be wrong!" :).

Hope this helps, & thanks for the excellent question!
Andrew D.
Content Manager, Next Step Test Prep.
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