GFR Physiology
Lecture given:
Table of Contents
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Objectives
Describe glomerular filtration and the glomerular filtration rate
- GFR: volume of fluid filtered from the renal glomerular capillaries into the Bowman's capsule per unit time (corrected for body surface area)
- Glomerular filtration: bulk flow of protein free plasma from the glomerulus into Bowman's space
- Same salt composition as plasma at the beginning
- Filtrate composition changes in its passage down the nephron
Describe how Starling Forces influence fluid movement a) between capillaries and interstitial fluid and b) between capillaries and Bowman's capsule
- Starling forces: (out of capillary is +)
- Capillary hydrostatic pressure (+)
- Interstitial fluid colloidal oncotic pressure (+)
- Capillary fluid colloidal oncotic pressure (-)
- Interstitial fluid hydrostatic pressure (-)
- Usually 0
- Movement to Bowman's capsule
- Size: small molecules (~5000) has easier time moving than larger molecules (Hgb ~68K, Albumin ~69k)
- Charge: Glomerular basement membrane is negatively charged, so will repel negatively charged molecules
- Autoregulation
- GFR maintained over a wide gradient of blood pressure
- Through dilation/constriction of A/Efferent arterials controlled by feedback loops, myogenic stretch responses and neurohormonal influences
- Aff art dilatation: prostaglandin, kinine, dopamin (low dose), ANP, NO
- Eff art constriction: Angiotensin II
- Aff art constriction: norepinephrine, endothelin, ADH, prostaglandin blockade
- Eff art dilatation: Angiotensin II blockade
- Juxtamedullary apparatus
- macula densa senses the ionic content of tubular fluid at the thick ascending limb/DCT
- stretch receptors cause renin release, which is involved in formation of angiotensin II and release of aldosterone
- In case of reduction in GFR:
- In case of increase in GFR:
- Macula densa sense increase in delivery and reabsorption of chloride
- vasocontrict afferent arterial
- Tubulo-glomerular Feedback
- inhibited by loop diuretics
Given the necessary information, calculate net filtration pressure
- Filtration = Kf (ΔP - Δπ)
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page revision: 7, last edited: 14 Apr 2012 21:30