Q20

[romanmuffin]

Tough passage. It was hard to wade through the scientific terms, etc.
Let me take a stab at it.

Line 35 introduces what happens when physiological and behavioral responses restore plasma osmolality to normal. Decrease in plasma osmolality > inhibits secretion of vasopressin > thirst is inhibited to prevent further dilution of bodily fluids.

Is this correct?

[rsmorale]

I'd like more insight on Q 20 as well. Thanks!

[timmydoeslsat]

For #20, the question stem is asking us what the withholding of vasopressin accomplishes which function as it relates to the restoration of plasma osmolality to normal levels.

First, we know that Lines 40 and 41 tell us that vasopressin is a peptide hormone that promotes water conservation in the kidneys, and that the withholding of vasopression is used when consumption of water is in excess of need.

So think of vasopressin as an object that is waiting on guard to release or secrete something that will promote water conservation.

As you might imagine, the body does not want vasopressin releasing its stuff when it is TRYING to get rid of excess water. That would be counterproductive.

So lets go to the answer choices:

A) Passage states on Line 43 that thirst is inhibited.

B) Looks good. It is mentioned on Lines 43-44. And is in the context of inhibiting vasopressin.

C) Vasopressin does this, but not the withholding of it.

D) No support for this. I think this is tempting you on information derived from the beginning of the second paragraph. This part was just telling us that when fluid moves around, obviously the levels of water and solutes will be different, but the body allows for a tolerance level of 1-2% between the two.

This does not involve vasopressin.

E) We know that vasopressin is a peptide hormone. When it is being withheld, we have no idea of what steroid hormones do. In fact, we are not told of one specific steroid hormone. Just that they exist.