A little help with a renal question?

[majik1213]

I don't seem to understand very well renal physiology because I cannot for the life of me understand why constriction of the ureter does nothing to RPF? My understanding is that RPF = (U*V)/(A-v), where U = urine solute concentration, A = renal artery plasma concentration, v = renal vein plasma solute concentration, and V = urine flow rate. But if you constrict the ureter, V drops to 0 because urine doesn't flow. How does RPF not fall with it?

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[Captopril]

I don't seem to understand very well renal physiology because I cannot for the life of me understand why constriction of the ureter does nothing to RPF? My understanding is that RPF = (U*V)/(A-v), where U = urine solute concentration, A = renal artery plasma concentration, v = renal vein plasma solute concentration, and V = urine flow rate. But if you constrict the ureter, V drops to 0 because urine doesn't flow. How does RPF not fall with it?

I hate math so I didn't even bother reading anything after that crazy formula. All you need to know is ureter constriction=backed up pee in kidney=back pressure at glomerulus=less filtration. Nowhere in that is RPF affected. So overall you get a low GFR and FF, RPF is still cool.

 

[Igor4sugry]

Renal plasma flow (RPF) tells us at what rate plasma is flowing through the renal capilary bed (peritubular bed). RPF will increase if: A. Increase systemic blood pressure B. Dilate afferent arteriole.

Filtration fraction (FF) tells you what % of plasma goes through glomerulus into the tubule.

In the case of tubular constriction you will have less plasma going through the glomerulus (decreased GFR). Your RPF should be unafected. But your FF will decrease.

 

[Captopril]

Renal plasma flow (RPF) tells us at what rate plasma is flowing through the renal capilary bed (peritubular bed). RPF will increase if: A. Increase systemic blood pressure B. Dilate afferent arteriole.

Filtration fraction (FF) tells you what % of plasma goes through glomerulus into the tubule.

In the case of tubular constriction you will have less plasma going through the glomerulus (decreased GFR). Your RPF should be unafected. But your FF will decrease.

that's the pointdexter version of what i said

 

[vicinihil]

I don't seem to understand very well renal physiology because I cannot for the life of me understand why constriction of the ureter does nothing to RPF? My understanding is that RPF = (U*V)/(A-v), where U = urine solute concentration, A = renal artery plasma concentration, v = renal vein plasma solute concentration, and V = urine flow rate. But if you constrict the ureter, V drops to 0 because urine doesn't flow. How does RPF not fall with it?

I think this is where logic prevails and math fails. Oh snap, I went there.

The original equation is....Input = output

RPF(a)*P(a) = RPF(v)*P(v) + UxV

If you make V = 0, the equation will still give you a value for RPF.