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nbme24/Block 2/Question#7

A 75-year-old man with a 10-year history of ...

Hydrostatic pressure in Bowman space

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submitted by guillo12(12),

Why there's no increase in Hydrostatic pressure in glomerular capillaries?

rihan  Between the glomerulus and Bowman's space there is a hydrostatic pressure gradient. This gradient is normally the result of a LARGE glomerular hydrostatic pressure and a LOW pressure in Bowman's space which normally favors filtration. Diagram here: http://physiologyplus.com/wp-content/uploads/2017/08/Glomerular-Filtration.png In the case of post-renal obstruction, hydrostatic pressure behind the blockade will rise and urine will reflux into the capsular space and renal tubules (while glomerular hydrostatic pressure is unaffected) effectively decreasing the pressure gradient which reduces the filtration rate. +1  




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submitted by famylife(32),

Not a full answer but it's a start (in the context of an obstruction): "Obstruction of urine flow results in an increase in hydrostatic pressures proximal to the site of obstruction. It is this buildup of pressure that leads to the accompanying pain, the distention of the collecting system in the kidney, and elevated intratubular pressures that initiate tubular dysfunction. In the first days of obstruction, the dilatation of the poorly compliant collecting system may be minimal. As the increased hydrostatic pressure is expressed in the urinary space of the glomeruli, further filtration decreases or stops completely." (Harrison's, 20e, Chapter 313)

trichotillomaniac  the key here is the term hydronephrotic kidney. anytime there is that, there is a post renal obstruction of some sort. The fact that he has progressive renal failure just contributes to the idea that his kidneys have seen damage before and are not able to withstand the pressure from the back up as well. I got tripped up on this. The important thing to note is that Hydronephrosis and dilation = back up = increased in volume pressure (hydrostatic) +1