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Old 05-10-2011
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Kidney Peritubular Capillary Pressure

Can anyone explain what this is and how/if it relates to GFR?
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Originally Posted by apx85 View Post
Can anyone explain what this is and how/if it relates to GFR?
Basically, the peritubular capillaries are AFTER efferent arterioles so they help in reabsorption. If the pressure is low, more fluid is reabsorbed. If the pressure is high, more fluid is secreted.

Heres an image -
http://www.elsevierimages.com/images...-0550x0475.jpg

Heres a detailed explanation from a source -

"Renal circulation is unique in that it has two capillary beds; the glomerular and peri-tubular capillaries which are arranged in series and separated by efferent arterioles that help regulate the hydrostatic pressures in both sets of capillaries. High hydrostatic pressure in glomerular capillaries (about 60 mm of Hg) causes rapid fluid filtration, lower hydrostatic pressure in peritubular capillaries (about 13 mm of Hg) permits rapid fluid reabsorption. By adjusting the resistances of afferent and efferent arterioles, kidneys regulate the hydrostatic pressures in both glomerular and peritubular capillaries, thereby changing rate of glomerular filtration or tubular reabsorption in response to body homoeostatic demands."

http://www.similima.com/phy16.html
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Old 05-10-2011
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Quote:
Originally Posted by Hope2Pass View Post
Basically, the peritubular capillaries are AFTER efferent arterioles so they help in reabsorption. If the pressure is low, more fluid is reabsorbed. If the pressure is high, more fluid is secreted.

Heres an image -
http://www.elsevierimages.com/images...-0550x0475.jpg

Heres a detailed explanation from a source -

"Renal circulation is unique in that it has two capillary beds; the glomerular and peri-tubular capillaries which are arranged in series and separated by efferent arterioles that help regulate the hydrostatic pressures in both sets of capillaries. High hydrostatic pressure in glomerular capillaries (about 60 mm of Hg) causes rapid fluid filtration, lower hydrostatic pressure in peritubular capillaries (about 13 mm of Hg) permits rapid fluid reabsorption. By adjusting the resistances of afferent and efferent arterioles, kidneys regulate the hydrostatic pressures in both glomerular and peritubular capillaries, thereby changing rate of glomerular filtration or tubular reabsorption in response to body homoeostatic demands."

http://www.similima.com/phy16.html
Let me simplify a bit... when you constrict the efferent arteriole, there is increase blood in the glomerullar capillary bed, so there will be more filteration into bowman's capsule. I believe Angiotensin II works on the Efferent arteriole, there by causing constriction, and increasing the GFR, and thereby increasing Na reabsorption (different topic)
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Originally Posted by patelMD View Post
Let me simplify a bit... when you constrict the efferent arteriole, there is increase blood in the glomerullar capillary bed, so there will be more filteration into bowman's capsule. I believe Angiotensin II works on the Efferent arteriole, there by causing constriction, and increasing the GFR, and thereby increasing Na reabsorption (different topic)
Let me add to this: When the efferent arteriole is going to constrict, pressure proximal to it will build up while pressure will decrease distal to it. That means hydrostatic pressure in the glomerulus increases, favouring filtration of fluid in the bowmans capsule. Similarly a decrease in pressure in peritubular capillaries favours reabsorption of fluid from tubules.
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Thanks guys!
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