Weird Renal Q on NBME 7 (the newest NBME)

[Captopril]

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So I just took NBME 7 last night...pretty fair questions, but I think the grading is a bit more stringent than the previous ones (or I got stupider). In any case I came across a weird situation in one of the Renal questions ***IF YOU PLAN ON TAKING NBME 7, DON'T READ ON***





So the question describes a dog or something which is given Angiotensin II. Then it asks which of the following changes will take place and lists a bunch. The weird part is, these were both options:

-The Filtration Fraction will increase
-The Renal Blood Flow will decrease (I understand RBF depends on Hct, but they specifically showed that Hct was constant so I assume that wouldn't be a factor)

Doesn't the latter preclude the former? To my understanding, both are taking place when you give angiotensin II b/c of it's vasoconstrictive affects on the efferent arteriole. Any takers?

 

[Sol Rosenberg]

.

 

[McGillGrad]

Wow, there's a NBME 7? The wonders never cease.

 

[DrTacoElf]

http://missinglink.ucsf.edu/lm/Renal_physio_modules/Final/WalkthroughTubule8_Efferent.gif

 

[Vergie]

On page 159 of BRS physio there's a table that shows constriction of efferent (it even uses angiotensin II as the example) as causing an increase in filtration fraction.

I remember that if you give too much angio II it can cause afferent constriction too which could cause no change in filtration fraction. So I dunno. Just throwing that out there. Maybe the question had another clue that would have narrowed it down.

 

[Captopril]

On page 159 of BRS physio there's a table that shows constriction of efferent (it even uses angiotensin II as the example) as causing an increase in filtration fraction.

I remember that if you give too much angio II it can cause afferent constriction too which could cause no change in filtration fraction. So I dunno. Just throwing that out there. Maybe the question had another clue that would have narrowed it down.

Yeah I probably did miss something in the stem, since there was a paragraph of erroneous BS preceeding the stem

 

[IceColdPenguin]

actually i was wondering this too, i put increase FF(cuz u KNOW rpf is decreasing and GFR is increasing) and that was right, but just seemed more right to me.. i dont know exactly why but im thinking maybe autoregulation? or increased volume of blood (aldo effect, but that would take a while methinks)

 

[xx216xx]

i think you might has missed something when reading it because i kind of remember that question and i had to re-read it a couple times because i remember thinking there were two answers at first but i eventually figured out that i read the answer choice wrong and so I went with the increased FF one. I'm pretty sure i was debating between the same two answer choices you're describing but there was a catch to the wrong choice, i just can't remember what it was though

 

[IceColdPenguin]

i have it screenshotted, i just went over my test, looked at it again i mean

unless the fact that the animal is anesthesized or the fact that they just give u the RBF = 200ml/min...

idunno?

 

[Sol Rosenberg]

Yeah, I agree with xxx216xxx -- I remember trying to choose between to the two, but then seeing something when I looked at it again, like "for the same renal blood flow," or something like that that made FF the definite answer.