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NBME 21 Answers

nbme21/Block 2/Question#8 (53.9 difficulty score)
A 55-year-old man is diagnosed with renal ...

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submitted by hayayah(1056),
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nleRa etyrar ossstien is oggni to ecdarees bolod lwfo to eth JG lselc snees eht scraeeed in fosirpneu sesurepr nad csereet ir.nne

ennRi is purddoce yb teh JG l,escl GJ elscl aer in het cetxro e(hyt aer oeidmfid thmoos secmlu fo eht treefnaf ieerl.atr)o

submitted by mambaforstep(22),

Question is asking what part of the kidney secreted renin.

order of thinking:

  1. Renin is made by the JG cells
  2. JG cells are "juxtaglomerular" to the glomeruls aka right next to the glomeruli (furthermore, they actually are modified smooth muscle cells of the AFFERENT arteriole FA pg 577)
  3. Glomerulus is in the renal corpuscle. "renal corpuscle is the blood-filtering component of the nephron of the kidney. It consists of a glomerulus - a tuft of capillaries composed of endothelial cells, and a glomerular capsule known as Bowman's capsule"-wikipedia
  4. Renal cortex "contains the renal corpuscles and the renal tubules except for parts of the loop of Henle which descend into the renal medulla" -wikipedia

TLDR; if renin is secreted by JG cells and JG cells are in the glomeruli which is in the renal corpuscle which is in the renal cortex, then JG cells are in the renal cortex so RENIN WILL BE HIGHEST IN CORTEX

djeffs1  I think I overthought this one. I initially thought all of the above, but then I thought, blood that isnt filtered goes in peritubular capillaries down into the medulla (where it becomes most concentrated -hence papillary necrosis in sickle cell) and therefore renin will be most concentrated there... +  

submitted by demihesmisome(4),

So I must have misunderstood - the arcuate arteries are in the cortex which is why I picked cortex - but we're saying the renin will always be highest in the cortex? - p. 564 FA

schep  This was my thinking, too. I didn't think about JG cells or where renal corpuscles are. I picked which part of the kidney is perfused by arcuate artery. I get jittery when I get these questions right for the wrong reason... +1  

submitted by _pusheen_(6),
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I tnihk stih one is elarillty utjs asgnki hawt tpra of het ekyndi lilw eb the stom poylor eudsferp. Ttah atrp uowld aveh teh msto irnne. l,oAs eth elalmud dnte’os haev JG lelsc so I sgues ast’th ohntaer neasor why it ’dulcont vahe eht msot n.nrie

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. 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. +12  
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. +6  
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 ._. +2