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Glomerular Filtration

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Biological Sciences

Intro to Renal Physiology & GLomerular Filtration I. Formation of the Ultrafiltrate a. Filtration Barrier—(3) fenestrae of endothelial cells, basement membrane, & slit membranes on podocyte foot processes i. 3 parameters determine whether solute will cross barrier: 1. size: <5200 A filter freely; > 34000 daltons not filtered *radius & MW are important!* 2. charge: (-) charge is retarded from crossing 3. shape: rod-shaped pass more easily than globular ii. concentration ratio—gives measure of how well solute crosses filtration barrier ([plasma solute]/[urine solute]) b. Physical Factors i. SNGFR = K(ΔP -fΔπ) = single nephron GFR 1. ΔP = change in hydraulic pressure between glomerulus (P ) & GC bowman’s capsule (P ) BC a. Normally, P GC = 45mmHg & P BC = 10mmHg 2. K =ffiltration coefficient = (hydraulic permeability of filtration barrier) x (filtration surface area) a. K ffr kidney is > 2x any other capillary network in body 3. Δπ = oncotic pressure difference across membrane = colloid osmotic pressure a. Rises from 20mmHg to 35 mmHg from afferent to efferent ends b/c plasma proteins are becoming more concentrated b. Since π of bowman’s space ~ 0 (no lg – proteins), Δπ = π GC c. Tends to pull H2O back into capillaries ii. Because glomerular capillaries lie between 2 arteries, hydraulic pressure is relatively constant throughout! iii. Very small net driving force, but large K fllows for high fluid flow rate c. Filtration Profiles
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