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NBME 22 Answers

nbme22/Block 1/Question#4

A 48-year-old man begins furosemide therapy for ...

Decreases the luminal permeability to Na+ in the collecting duct

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I got that it needed to be a potassium sparing diuretic. Is there a reason it cannot be an aldosterone antagonist? I chose blocks basolateral K+ channels as these decrease the basolateral K+/Na+/ATPase because the wording of the correct answer did not make sense to me -- assuming they were going for an ENaC blocker (and that decreased luminal permeability indicates that Na+ would be remaining in the lumen, not remaining in the principal cell as I originally thought).

luckeroo  I think the reason it’s a potassium-sparing diuretic rather than an aldosterone antagonist has less to do with why the aldosterone antagonist cannot be used and more to do with the fact that a potassium-sparing diuretic would be more of a “first-line” adjunctive diuretic treatment. +1  
luckeroo  As for the answer choice, potassium sparing diuretics achieve their overall anti-aldosterone effect by competitively inhibiting aldosterone receptors on the interstitial side (decreasing the Na/K-ATPase effect of shunting Na into the blood), thereby decreasing the gradient for sodium to enter the cell from the luminal aspect, blocking ENaC. +2  
yotsubato  There is no such thing as "Basolateral K Channel" there is only basolateral Sodium Potassium Pumps which are controlled by aldosterone. FA pg 573 +6  
nwinkelmann  @yotsubato LOL.... why didn't I think of it that what?! (by the way, that LOL is for me). The only basolateral K channel is the nephron (based on the first aid picture) is in the thick ascending limb of the loop of henle. +  
hello  Spironolactone and eplerenone are potassium-sparing diurectics that inhibit the Na/K ATPase, so I'm not sure what @luckeroo is referring to. Spironolactone and aplerenone are both ALDO antagonists. Na/K ATPase is found on the basolateral membrane. None of the answer choices fit with this. Amiloride and triamterene are also potassium-sparing diuretics; their mechanism is to block ENaC channels on the luminal membrane, this is choice "B." +1  




 +1  upvote downvote
submitted by hello(79),

Spironolactone and eplerenone are potassium-sparing diurectics that inhibit the Na/K ATPase. Na/K ATPase is on the basolateral membrane. None of the answer choices fit with this.

Amiloride and triamterene are also potassium-sparing diuretics. The mechanism is to block ENaC channels on the luminal membrane, this is choice "B."





Should use a potassium-sparing diuretic (FA 591). Triamterene and amiloride work by blocking ENaC channels.





 +0  upvote downvote
submitted by usmle11a(14),

spironolactone acts as an aldosterone antagonist which means decreasing Na+ permeability