Inc plasma conc. does not change Renal Plasma Flow. Why not?

[BlondeCookie]

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I have a question about renal physiology from confusion after reading a table 6-6 in Costanzo's Physiology text.

Apparently, increased plasma protein concentration does not change RPF (Renal Plasma Flow). Why not? I thought that the increased plasma proteins would lead to less GFR (Glomerular Filtration Rate) and thus, a higher amount of fluid staying in the renal blood. So, wouldn't you have an increase in RPF?

 

[MikeyK]

Plasma protein concentration has nothing to do with renal plasma flow. RPF is only changed by afferent/efferent arteriole constriction/dilatation. However increased plasma protein increases plasma oncotic pressure, leading to a decreased filtration fraction whaen you calculate the starling forces. Thus GFR is decreased but RPF is constant, which leads to a decrease overall Filtration Fraction (GFR/RPF).

 

[BlondeCookie]

Plasma protein concentration has nothing to do with renal plasma flow. RPF is only changed by afferent/efferent arteriole constriction/dilatation. However increased plasma protein increases plasma oncotic pressure, leading to a decreased filtration fraction whaen you calculate the starling forces. Thus GFR is decreased but RPF is constant, which leads to a decrease overall Filtration Fraction (GFR/RPF).

Thanks for the superb explanation. It's a simple concept and I was complicating things a bit. Thanks again for clearing that up.