Updated: 9/4/2020

Filtration

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Introduction
  • Filtration fraction (FF) represents the ratio between glomerular filtration rate (GFR) and renal plasma flow (RPF)
    • this in turn represents which fraction of RPF becomes filtered via the glomerular capillaries
      • the normal filtration fraction is ~20% and thus implies that 80% of the RPF is not filtered
        • the unfiltered RPF will then be part of the peritubular capillary blood flow after entering the efferent arteriole
    • Filtration fraction (FF) = GFR / RPF
    • Filtered load = GFR x plasma concentration
  • Renal plasma flow (RPF)
    • can be determined by using clearance of para-aminohippuric acid (PAH)
      • RPF = [U(PAH) x V] / [RA(PAH) - RV (PAH)]
        • U(PAH) = urine concentration of PAH (mg/mL)
        • V = urine flow rate (mL/min)
        • RA(PAH) = renal artery concentration of PAH (mg/mL)
        • RV(PAH) = renal vein concentration of PAH (mg/mL)
    • determining the RPF will allow you to determine the renal blood flow (RBF)
      • RBF = RPF / (1 - hematocrit)
 
Changes in Starling Force and Its Effect On RPF, GFR, and FF
Condition
RPF
GFR FF (GFR/RPF)
Afferent arteriole constriction
  • Unchanged
Efferent arteriole constriction

↑ plasma protein concentration
  • Unchanged
↓ plasma protein concentration
  • Unchanged
Ureter constriction
  • Unchanged

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