Physiology - An Illustrated Review (Thieme's Illustrated Review Series) by TannerThies Roger

Author:TannerThies, Roger [TannerThies, Roger]
Language: eng
Format: epub
Publisher: Thieme Medical Pub
Published: 2011-10-06T00:00:00+00:00

16.3 Limitations of Tubular Transport

The capacity of the tubules to secrete and reabsorb is not infinite. Rates reach an upper limit either because the transporters saturate (Tm-limited transport processes) or because the substance leaks back across leaky tight junctions (gradient-limited transport processes).

Saturation of Transporters: Tm-limited Transport Processes

Maximum tubular transport capacity (Tm) is the highest attainable rate of tubular transport of any given solute. Tm is reached due to saturation of the transport carriers and/or saturation of transport sites for a particular substance along the renal tubules.

– Substances with a reabsorptive Tm include glucose, phosphate, and sulfate ions, many amino acids, and Krebs cycle intermediates.

– Substances with a secretory Tm include PAH, uric acid, creatinine, histamine, and drugs (e.g., penicillin and morphine).

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