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glomerular filtration rate ( GFR) estimates

how much blood passes through the glomeruli each minute


GFR calculation

GFR = inulin clearance = (Urine concentration of inuline x urine flow rate ) / plasma concentration of inulin = Starling equation


Normal GFR -=

100 ml / min


Starling equation GFR

GFR = Kf ( ( Pgc - Pbs ) - ( π gc - πbs))
gc : glomerular capillary
bs : bowman space
Kf : filtration constant
πbs = 0


creatine clearance - clinical relevance

it is an aprroximate measure of GFR -- > slighlty overestimates GFR because creatinine is moderaterly secreted by rena tubules


chronic kidney disease - GFR measure

incremental reductions in GFR define the stafesof chronic kidney disease


creatinine serume concentration

0.6 -1.2 mg/ dl or 53-106 μmol/L


• What is the unit of measurement for the glomerular filtration rate (GFR)?

Volume over time; usually measured in milliliters per minute (mL/min), similar to clearance


• Exogenous ____ (inulin/creatinine) or endogenous ____ (inulin/creatinine) is used to calculate GFR, which is normally about ____ mL/min.

Inulin (freely filtered, neither reabsorbed nor secreted); creatinine (yields slight overestimate, is secreted in tubules); 100 mL/min


• Inulin is infused into a patient to assess renal function. What can it be used to measure, and how?

Inulin clearance (GFR = urine inulin concentration times urine flow rate divided by plasma inulin concentration [Uinulin × V/Pinulin])


• Creatinine clearance ____ (overestimates/underestimates) glomerular filtration rate as creatinine is ____ (secreted/reabsorbed) by tubules.

Overestimates; secreted (the plasma concentration of creatinine is slightly lower than it would be from filtration alone)


• Which formula calculates the glomerular filtration rate (GFR) by relating the glomerular capillary (GC) and Bowman space (BS) pressures?

GFR = Kf [(PGC - PBS) - (ΠGC - ΠBS)], where Kf = filtration constant; P = hydrostatic pressure difference; Π = oncotic pressure difference


• Incremental ____ (reductions/elevations) in GFR define the stages of chronic kidney disease.


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