Gfr

[Untitled121]

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.GFR may be maintained by afferent arteriole dilation and efferent arteriole constriction

How does this happen? I thought by dilating the afferent arteriole = BP drop = Less blood would be pushed to go through the glomeruli (i.e. the "potential difference" would decrease)?

Thanks to all
.

 

[eightball]

.GFR may be maintained by afferent arteriole dilation and efferent arteriole constriction

How does this happen? I thought by dilating the afferent arteriole = BP drop = Less blood would be pushed to go through the glomeruli (i.e. the "potential difference" would decrease)?

Thanks to all
.

pure physics...think garden hose.

Constrict the distal end of the garden hose, what happens the the pressure within the hose?

 

[Untitled121]

pure physics...think garden hose.

Constrict the distal end of the garden hose, what happens the the pressure within the hose?

Pressure within the hose will increase.

But that is akin to afferent rather than efferent, right?

 

[Milly12]

The afferent arteriole takes blood to the glomerulus. The efferent arteriole takes blood away from the glomerulus.

If you dilate the afferent, while keeping the efferent the same, more blood gets the glomerulus, thus more blood is filtered.

Think if you dilated the proximal part of the garden hose. The distal part stays the same. So where it's dilated, more water flows there and the same amount is exiting the efferent arteriole. So it's like pinching off the end of the efferent (distal or end of the hose). More water will be flowing around the afferent or proximal part of the hose and would be forced toward the glomerulus of there were a glomerulus.

Hope that helped or at least didn't confuse you.

 

[Untitled121]

Quote: If you dilate the afferent, while keeping the efferent the same, more blood gets the glomerulus, thus more blood is filtered.

If the proximal part of the garden hose is dilated, the pressure would drop and more water would come out BUT at a slower rate?

 

[pharmwannebe2]

"How does this happen? I thought by dilating the afferent arteriole = BP drop = Less blood would be pushed to go through the glomeruli (i.e. the "potential difference" would decrease)?"

Like you said before at the top, the book says that if you dilate afferent arterioles that will lead to constriction of efferent arterioles...remember body tries to maintain homeostasis. So when you get too much fluid, the kidneys will constrict efferent arterioles to help get fluid filtered into glomerulus. This constriction of efferent arterioles will cause BP to become elevated.

if you still don't get it: youtube video: http://www.youtube.com/watch?v=puM5WCvOBdU&feature=related

 

[Untitled121]

I referred to Poiseuille's Law and I have now got the concept sorted. --> http://en.wikipedia.org/wiki/Hagen–Poiseuille_equation#Electrical_circuits_analogy

The resistance is inversely proportional to radius. When the radius increases (i.e. in the case of afferent dilatation), the resistance decreases. Therefore, blood is able to flow at a quicker rate into glomeruli, thus maintaining GFR (and vice versa for efferent).