Renal clearance Clearance value Measure of volume of

Renal clearance

Clearance value • Measure of volume of plasma completely cleared of the substance per minute by the kidneys. • Renal excretion rate of the substance / concentration of the substance in arterial plasma • UV/P

Clearance value • Eg : Urea clearance 20 mg/ml X 1 ml / min 0. 3 mg/ ml • 67 ml/min

Applications • • To measure GFR Estimate tubular secretory capacity Measure renal plasma flow Measure osmotic and free water clearance

To measure GFR • • Freely filtered Not reabsorbed or secreted Non toxic Not metabolized into other substances Should not alter GFR Not stored in the kidney Easy to measure

To measure GFR Eg: • Inulin • Creatinine • Sodium ferrocyanides • Sorbitol • Radioactive cobalt labeled Vit B 12 • Radio iodine labelled hypaque

To measure GFR • Inulin clearance • 127 ml/min • Significance • Creatinine clearance • 80 – 110 ml/ min • ? ?

Estimate tubular secretory capacity • PAH

Measure renal plasma flow • Ficks principle • Amount of substance taken / min = (A-V) difference of the substance X Blood flow • Therefore : Blood flow / min = Amount of substance taken/min (A-V) difference of the substance • In kidneys? ?

Measure renal plasma flow • Completely extracted from blood each passage • Actively secreted by the tubules from blood into the lumen • • • Non toxic Should not alter RBF Not metabolized into other substances Not stored in the kidney Easy to measure

Measure renal plasma flow • Ficks principal in kidneys? ? Blood flow / min = UV/P

Measure renal plasma flow Eg: • Diodrast • PAH

Measure osmotic and free water clearance • Amount of water necessary to excrete the osmotic load in urine that is isotonic to plasma • Cosm = Uosm X V / P osm • Free water clearance • CH 2 O = V – Cosm.

Endocrine functions of KIDNEY • RENIN • ERYTHROPOIETIN • Active form of VIT D 3