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NBME 21 Answers

nbme21/Block 2/Question#8

A 55-year-old man is diagnosed with renal artery ...

Cortex

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submitted by hayayah(413),

Renal artery stenosis is going to decrease blood flow to the kidney. JG cells sense the decrease in perfusion pressure and secrete renin.

Renin is produced by the JG cells, JG cells are in the cortex (they are modified smooth muscle of the afferent arteriole).





I think this one is literally just asking what part of the kidney will be the most poorly perfused. That part would have the most renin. Also, the medulla doesn’t have JG cells so I guess that’s another reason why it couldn’t have the most renin.

sklawpirt  Exactly, it has to do with where in the kidney renin is released and requires a bit of knowledge of the artery branches that give rise to the afferent arteriole in the first place and where this branch point is located. http://anatomyforme.blogspot.com/2008/05/histology-of-kidney-lot-to-process.html Where renin production occurs in JGA cells, EPO production occurs in the renal peritubular interstitium (especially the proximal renal tubule, corext and some of the outer medulla.) Thus with the same questions stem it might ask where is concentration of EPO the highest? [And it would still be the cortex, with lower concentrations in the outer medulla, lowest concentration in the inner medulla, and none found in the papilla or renal pelvis. +6  
hayayah  Actually, the renal medulla receives significantly less blood flow than renal cortex. So the medulla is the one that's very sensitive to hypoxia and vulnerable to ischemic damage. I don't think this question is related to "what area is the most poorly perfused." It's just knowing that renal artery stenosis is going to decrease blood flow to the kidney. JG cells sense the decrease in perfusion pressure and secrete renin. Knowing that renin is produced by the JG cells and that JG cells are in the cortex should be enough to answer this question. +2  
cry2mucheveryday  I thought all the renin would collect in the pelvis where the arteries whould drain into a common vein and changed my answer to pelvis ._. +1