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Old 04-23-2012
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Kidney Why not the kidney autoregulate GFR?

Hello all,

I had a question regarding renal blood flow (RBF). In BRS physiology it mentions that there is autoregulation of RBF, accomplished through changing renal vascular resistance. It says that RBF can remain constant over arterial pressures of 80 to 200 mm HG, and it is done through myogenic mechanisms (where the renal afferents contract in response to stretch), and through tubuloglomerular feedback (where increased renal arterial pressure causes increased fluid delivery to the macula densa, and a responsive contraction of nearby afferent arterioles).

My question is that if the kidney can autoregulate RBF, and keep it constantly over different arterial pressures, how come things that increase increase or decrease blood volume or blood pressure change GFR? For example, congestive heart failure, reduces blood pressure, reduces renal perfusion, and sources say that it causes a decrease in GFR. How come the kidneys don't autoregulate and maintain constant GFR? Similarly, an increase in blood volume (i.e., from pregnancy), causes an increase in GFR... again why doesn't don't the kidney's autoregulate to maintain constant GFR?

Maybe I am just missing something obvious, but I am a little confused.

Thanks for your help in understanding this.
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Old 04-23-2012
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Actually it does regulate GFR too.. But in cases of heart failure, the reduction in flow is way beyond this capacity to regulate GFR..
And also if its a chronic failure, this regulation well lead to thickning and damage to the capillaries that will lead to renal failure and impaired renal function that will lead to decreasing GFR..
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Old 04-23-2012
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The autoregulation is limited and it's generally meant for acute situations. If you maintain a chronically high GFR by secreting more renin/angiotensin, you'll also raise your blood pressure via angiotensin/aldosterone. It's a reasonable response to acute stress, but not to chronic disease.
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Physiology-, Renal-

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