III: Renal Filtration & Blood Flow Flashcards
What is the Net Filtration Pressure (NFP)?
the algebraic sum of the Starling forces that favor and oppose glomerular filtration
Why is the filtration coefficient (Kf) so large in glomerular capillaries?
the capillaries are fenestrated (high permeability) and loop around (high surface area)
What would happen with an increased oncotic pressure in the glomerular capillaries?
more filtrate would be pulled out of Bowman’s space and back into the blood
Why is oncotic pressure in Bowman’s space negligible?
this is because any proteins that do make it through into the filtrate are rapidly taken up by pinocytosis and therefore do not contribute to the oncotic pressure
What is the equation for GFR?
GFR=Kf x NFP
What happens to Starling forces as arterial blood flows through glomerular capillaries from afferent to efferent sides?
- hydrostatic pressure in capillaries decreases only slightly (can consider it constant)
- oncotic pressure in the capillaries increases greatly due to concentration of proteins that cannot filter out
- hydrostatic and oncotic pressures in Bowmans space remain the same
How does pressure in the glomerular capillaries compare to systemic pressures?
mean pressure is higher in glomerular capillaries compared to peripheral capillaries and skeletal muscle capillary beds
List some renal diseases and how they affect GFR.
- prerenal (ex: heart failure)- decrease in circulating volume = decrease in GFR
- intrarenal (ex: glomerulonephritis, proteinuria)- immune complex deposition in glomerulus = decrease in GFR
- leaky glomerular capillaries- increase in Kf = increase in GFR
- postrenal (ex: hydronephrosis, kidney stones)- increase in BS hydrostatic pressure = decrease in GFR
Why can proteinuria cause an increase OR a decrease in GFR?
- protein in the urine increases oncotic pressure in the BS, thereby increasing GFR
- protein deposition in the glomerulus may clog up fenestrations, thereby decreasing GFR
What are urinary casts typically seen with?
low urine flow, acidic conditions, and proteinuria
What is glomerulonephritis?
It refers to a group of diseases that injure the basement membrane of glomerular capillaries, causing inflammation. Loss of glomerular integrity results in RBCs and casts in the urine.
How do changes in afferent and efferent arteriolar resistances affect RBF?
- constriction of afferent or efferent = decreased RBF
- dilation of afferent or efferent = increased RBF
What is the equation for renal blood flow (RBF)?
(Press. renal artery - Press. renal vein) / Resis. renal vasculature
In which part of the glomerulus is the highest RBF?
renal cortex due to high vascularization (cortex gets 90% of RBF)
Where do the highest decreases (largest drop-offs) in pressure occur?
in afferent and efferent arterioles
