Bio (EK lecture #144)

[IlyaR]

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This question seems to have 3 answers to me. I understand why A could be an answer, but I don't get how B and especially C are wrong.

Water diffuses out in the descending loop, which would make the filtrate less voluminous as compared to when it entered. Also, Isn't the very definition of concentrating urine that it gets more concentrated as goes through the loop of Henle?

 

[sps27]

I would have selected B as the ans. The descending thin section of the LOH is permeable to water and urea but not the salts. The ascending thin section is permeable to salts and urea, but not water. So the filtrate is loosing water in the descending thin section because medula is hypertronic than filtrate and then filtrate becomes more dilute in the ascending thin section because it is now loosing salts. The ascending thick section of LOH is permeable to salts but not permeable to water and urea, so once again the filtrate becomes more dilute as it passes through DCT and collecting tubule.

But it seems like the overall effect of the filtrate in the LOH is to make the medulla more hypertronic than filtrate so that water can be reabsorbed. Because there is no water reabsorbtion in DCT and collecting duct. So I guess it makes sense to say that LOH concentrates the medulla.

Let me know I am wrong in my understanding.

 

[gettheleadout]

C is definitely a true statement. EK sucks.