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Renal Clearance: II

RENAL PHYSIOLOGY

PRINCIPIE OF TUBULAR SECRETION LIMITATION (Tm) USINC PARA-AMINOHIPPURATE (PAH) AS EXAMPLE

At Tm

Conceniration of PAH in plasma is just sufficient to saturate secretory capacity of tubule

Below Tm

Conceniration of PAH in plasma is less than secretory capatily of tubule; plasma passing through functional kidney lissue is entirely deared of PAH

Abovc Tm

*l Conceniration of PAH in plasnu exceed$ secretory capacity of tubule; plasma passing through functional kidney lissue is not entirely cJcared of PAH

120- 100-
-- 80		Secreted
|f 60-	//
X	/;
£ 40-
20-
	10	20 30

Amount _ Amount , Amount excreted filtered secreted

Plasma PAH (mg/dL)

Figurę 6.7 Renal Handung of para-Amino Hippurate (PAH) .

PAH approximates the renal plasma flow. As the plasma concer tion PAH is increased, the secretory capacity of the proximal te-is exceeded and the renal clearance of PAH decreases.

PAH is filtered at the glomerulus and secreted into the tubular fluid by the proximal tubule. At Iow plasma PAH concentrations, virtually all the PAII is excreled into the urine. At this point the c learance of