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To my current understanding, stenosis or narrowing of the arteries would mean higher blood pressure, similar to atherosclerosis. So the Renin system should be suppressed to counter the high blood pressure. But..

I have read in a textbook that renal artery stenosis means lower blood flow in the kidney due to the narrowing of the artery. Thus the Renin system is activated to increase blood pressure.

So why does narrowing of the renal artery cause a decrease in blood pressure, and not increase?

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  • $\begingroup$ Read your own question closely; the answer is right there. What purpose does the renin-angiotensin system serve normally? How is blood pressure determined at different places in the body? Why would a reduced blood pressure in the kidney elicit activation of renin-angiotensin system? How would that affect the rest of the body? $\endgroup$ – anongoodnurse Jan 2 '15 at 3:49
  • $\begingroup$ I understand how the renin-angiotensin system works. What I do not understand is why a stenosis in the renal artery leads to a decrease in blood pressure whereas atherosclerosis in other blood vessels leads to a increase in blood pressure. Aren't both narrowing of the blood vessels? So why the different outcomes? $\endgroup$ – Bob Jan 2 '15 at 4:54
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So why does narrowing of the renal artery cause a decrease in blood pressure, and not increase?

It doesn't. It causes an increase.

If the blood flow to the kidney is decreased for any reason (for example, hemorrhage or dehydration), the kidney is one of the organs that will protect it's perfusion by causing an increase in BP through the renin-angiotensin-aldosterone system (RAAS).

Very briefly: decr. blood flow -> renin secretion by juxtaglomerular cells -> conversion of serum Angiotensinogen into Angiotensin I (+ ACE) -> Angiotensin II => elevated BP (by a host of mechanisms).

If there is renal artery stenosis, the kidney will try to compensate for this (locally) reduced blood flow by activating the RAAS. The kidney doesn't 'know' that the blood flow/pressure is only locally reduced. It will cause systemic hypertension as a way to increase it's blood flow.

Atherosclerosis is a whole different ball of wax.

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