Renal Question

[juddson]

The equation for Glomerular Filtration Rate (GFR) is:

GFR = Kf x [P(gc) - P(bc) - pi(gc)]

I guess what I'm having trouble with is understanding how GFR could be low in the presence of protein and/or blood in the urine. Prontinurea and/or hematuria suggests a breakdown of the filtration barrier, which effectively raises Kf to extremely high levels (ie., raises the permeability constant to almost infinity). Is it really possible that perfusion pressure across the glomerular capillary beds could be so low as to overwhelm the extremely high Kf and therefore lower GFR? By what mechanism can large solutes like proteins, RBC and WBC's pass the glomerular capillaries into the Bowman's capsule and yet the nephron experience low GFR? Or am I missing something?

Judd

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[bnichols0330]

I believe it has to do with the difference in osmotic pressure. If protein is leaking into the glomerulus, then the osmotic pressure gradient is less. If this is the case then there is less driving force for water to cross the membrane and therefore decreased GFR.

Also, remember that GFR is not simply how much "stuff" passes into the glomerulus, but rather how much volume is filtered by the glomerulus.

I don't know if this helps or not, but good luck.

 

[Skialta]

Also remember that at low flow there is longer relative time for reabsorption.

 

[omarsaleh66]

The equation for Glomerular Filtration Rate (GFR) is:

GFR = Kf x [P(gc) - P(bc) - pi(gc)]

I guess what I'm having trouble with is understanding how GFR could be low in the presence of protein and/or blood in the urine. Prontinurea and/or hematuria suggests a breakdown of the filtration barrier, which effectively raises Kf to extremely high levels (ie., raises the permeability constant to almost infinity). Is it really possible that perfusion pressure across the glomerular capillary beds could be so low as to overwhelm the extremely high Kf and therefore lower GFR? By what mechanism can large solutes like proteins, RBC and WBC's pass the glomerular capillaries into the Bowman's capsule and yet the nephron experience low GFR? Or am I missing something?

Judd

I think the answer is that if your glomerulus process is messed up you wont see as much protein or RBCs in the urine because all this stuff gets clogged in the glomerulus so thats why in hematuria of glomerular processes, u see RBC casts (a bunch of RBCs clumped together that finallly come out in the urine) when there's enough back pressure.

So to answer your question, the GFR is probably low cuz the glomerulus is clogged with RBCs and proteins or immune complexes. Sounds like u are talking about nephritic syndrome (renal failure, can't pee, kidney shuts down so high creatinine and BUN) instead of the nephrotic syndrome (u are peeing out a lot of protein, and u lose oncotic pressure, and get symptoms related to protein loss: hypercoagubility, hyperlipedimia)


later

Omar