Renal Physio Q Discrepancy

[MoscowAbe]

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This is one of those up down arrow questions where there is a discrepancy between FA and UW.

What happens to GFR in efferent arteriole constriction?

FA says increase

UW says decrease

 

[metalmd06]

Constriction of the efferent arteriole definately increases GFR (it increases glomerular capillary hydrostatic pressure, which is the main driving force for filtration)

 

[MoscowAbe]

Constriction of the efferent arteriole definately increases GFR (it increases glomerular capillary hydrostatic pressure, which is the main driving force for filtration)

Thats how I thought of it, but than got confused after seeing two variant answers.

Thanks 👍

 

[Doc176]

Thats how I thought of it, but than got confused after seeing two variant answers.

Thanks 👍

Well I think i came accross such a question.There were two questions
one was asking about angiotensin II's effect and the other was asking for just simple efferent arteriole constriction

answer to the first one is Decreased GFR and the answer to the second one is increased GFR. What question r u referring to

 

[knuckles]

Wouldn't angiotensin 2 cause increased TPR overall, but constrict efferent arteriole constriction, maintaining GFR constant (or something like that)

 

[eddie13231]

Wouldn't angiotensin 2 cause increased TPR overall, but constrict efferent arteriole constriction, maintaining GFR constant (or something like that)

Yes to both. Thats why pts taking an ACE can have increasted creatine when beginning the drug.

They can also get hyperkalemia, hyponatremia, acidosis (aldosterone decreased).

 

[match2011]

angiotensin II constricts efferent arteriole, increase GFP

dose-dependent constrict efferent and afferent arterioles, then decrease GFP

 

[username456789]

The way we were taught, efferent constriction definitely increases FF; however, due to possible changes in oncotic pressures or something (I forget) its effects on GFR are much less predictable, despite everyone's knee jerk reaction to say "it increases GFR."

it's ****ty of anyone to ask that question on Step I.

 

[Doc176]

The way we were taught, efferent constriction definitely increases FF; however, due to possible changes in oncotic pressures or something (I forget) its effects on GFR are much less predictable, despite everyone's knee jerk reaction to say "it increases GFR."

it's ****ty of anyone to ask that question on Step I.

Yeah that may be the point here.Increased FF leads to increased oncotic pressure in the peritubular capillaries causing much of the filtered fluid to be reabsorbed along the length of the tubule.
in the question I was referring to the patient had secondary increase in angio II due to edema and hypotension keeping this in mind his GFR was already low to begin with.

Still I have come across such question in Kaplan Q bank in one of that they gave angio II to an animal in experiment and asked about the GFR
they said it decreases although the decrease is very small compared to the fall in RPF.

But if I think about it as angio II will also cause some constriction of afferent arteriole so either GFR should remain the same or decrease slightly

 

[IMGUSMLEStep1]

Efferent constriction: ++ GFR

ATII constricts efferent > afferent, so it "preserves glomerular capillary pressure as renal plasma flow decreases. Thus, GFR may show only a minimal decrease under these conditions." (quoted from Kaplan)

 

[MoscowAbe]

Ok so I looked up the question its # 1016,

Its a situation were a person is hypovolemic and they're asking what physiological changes occur.

I answered

RPF - GFR + FF+

The correct answer is

RPF -- GFR - FF+

So I guess what they're saying is GFR is still decreased but much less so due to compensatory mechanisms. Its really a confusing way to ask this question.