Substance freely filtered by kidney

Ans: b (Inulin) Ref: Ganong 22nd ed/ p.706, 21st ed/ 709The substance which is freely filtered and neither absorbed nor secreted in the tubules is inulin.Creatinine is practically used to measure GFR, because it is easy to measure.Creatinine is secreted by the tubules and some maybe reabsorbed.Clearance of a substance is equal to the concentration of that substance in urine multiplied by urine flow rate divided by arterial plasma level, i.e.Clearance = UxV/PxUx = concentration of substance in urineV - urine flow ratePx = concentration of the substance in plasmaNote:PAHA is used to measure renal plasma flow i.e.Clearance of PAHA is equal to effective renal plasma flow.From the renal plasma flow, the renal blood flow can be calculated by:Renal blood flow = RPF x 1/ (1-Hematocrit)Renal blood flow = 1273ml/min which account for about 25% of cardiac output.