Overview Glomerular Filtration Rate (GFR) GFR is an important clinical tool used to assess patients with kidney disease this is an index of functional renal mass therefore, this data point can be used to determine the severity and course of renal disease Fluid movement across the glomerulus follows Starling's law GFR = Kf [(PGC - PBS) - (πGC - πBS)] Kf is filtration coefficient login to view 1 more bullet PGC is hydrostatic pressure in glomerular capillaries login to view 2 more bullets PBS is hydrostatic pressure in Bowman's space login to view 1 more bullet πGC is oncotic pressure in glomerular capillaries login to view 2 more bullets πBS is oncotic pressure in Bowman's space login to view 1 more bullet Glomerular filtration rate and arteriolar resistance the glomerular capillaries are between the afferent (precapillary) and efferent (postcapillary) arteriole e.g., a drop in renal perfusion pressure (e.g., hypotension) stimulates the activation of the renin-angiotensin system which produces angiotensin II login to view 3 more bullets Measurement of Glomerular Filtration Rate (GFR) GFR measurement (inulin) C(inulin) = GFR inulin is freely filtered across glomerular capillaries and is neither reabsorbed nor secreted inulin is a glomerular marker C(inulin) = [U(inulin) x V] / P(inulin) = GFR C(inulin) is clearance of inulin (mL/min) U(inulin) is urine concentration of inulin (mg/mL) V is urine flow rate (mL/min) P(inulin) is plasma concentration of inulin (mg/mL) normally, GFR ≈ 100 mL/min GFR measurement (creatinine) C(creatinine) ≈ GFR creatinine is freely filtered across glomerular capillaries and is moderately secreted by peritubular capillaries into tubular lumen login to view 2 more bullets