renal failure

[MDwannabe7]

If someone has renal failure in which their nephrons cannot actively secrete or reabsorb anything - what will their kidneys still be able to do?

Since they can't actively do anything - the passive processes still function - reabsorption of water and salt, etc... Therefore, since the passive processes are drive by diffusion - basically whatever is filtered into the nephron should be isotonic to the blood - right?

So why do I have that the correct answer is that the kidney will still be ale to produce hypotonic urine?

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[AZFutureDoc]

I don't really see how this would work, since there are so many locations of concentrating urine. I don't get how the bowman's capsule, proximal convulated tubule, ascending loop of Henle, distal convoluted tubule, collecting tubule, and collecting duct would all simultaneously stop functioning.

I think something is getting lost in your paraphrase, because a question like this seems like something that would follow a passage where we describe "complete renal failure" since to me, this is a very vague term.

If I had this as a discrete on my MCAT, I would still say we get hypotonic urine... ADH can still act on the collecting duct, and the look of Henle will still have its concentration gradient remotely intact due to the endeavors of the vasa recta. Furthermore, if there were problems in the functioning of the juxtaglomerular app, more filtrate, with more particles (since we now have cells and proteins) would be allowed in. If the only problem you had was a faulty JgA, then you would have more solutes in any given amount of urine, thus higher tonicity.

So you would make urine that is not quite as concentrated, but still more hypotonic than the blood.