Studies on Kidney Function

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Abstract
This work is based on the assumption that creatinine is eliminated solely by filtration and is not at all reabsorbed by the tubules. The index of concentration, C, is defined as the ratio of urine creatinine concentration to plasma creatinine concentration; the latter was raised by ingestion of creatinine. The formula Br% = C/C-1 Bp%-1/C-1 Bu% then holds, where Br%, Bp% and Bu% are the concentrations in the reabsorbed fluid, the plasma and the urine, respectively, of the substance B. The urea and chloride concentrations of the reabsorbed fluid are thus calculated. Since the urea concentration of the reabsorbed fluid is found to be always less than that of the plasma, while the chloride concentration of the reabsorbed fluid is greater than that of the plasma when the plasma concentration is below 375 mgm.%, it is concluded that urea reenters the tubules by a mere back diffusion, while chloride is a true threshold substance, being actively reabsorbed. When the plasma chloride content is above 375 mgm. %, chloride is treated as a no-threshold substance. Arguments are presented in favor of the view that chloride and other threshold substances are reabsorbed together with most of the water in the proximal convoluted tubules.

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