Q17

[cyt5015]

Is E wrong because of Vasopressin not being a mechanism for diluting plasma osmolality?

[rinagoldfield]

hi cyt! Thanks for your post.

The author discusses vasopressin in the second paragraph. We discover there that vasopressin is a peptide hormone that helps regulate the level of solutes in extracellular fluid. When we’ve got too much water, vasopressin is suppressed and thirst is shut down. This allows the solute/fluid ratio to increase. On the flip side, when we don’t have enough water, vasopressin is released and thirst is spiked. This allows the solute/fluid ratio to decrease.

(B) is supported; vasopressin is important for maintaining homeostatis in cases of increased osmolality (not enough water!) and decreased osmolality (too much water!). Lines 36-52 detail these processes.

(E) is tempting! I see why you liked this answer choice. BUT we know that "thirst is stimulated ONLY AFTER vasopressin has been released" (lines 52-54, emphasis added). (E) flips this order around.

(A), (C), and (D) bring in steroid hormones, which are irrelevant here.

Hope that helps, cheers.