18 



Physiology of the Kidney 



•CRCATrNlNr T^. .|6MGM./MIM 

 INULIN 



"GLUCOSE lOO 

 VITAMIN C 

 CREATININE 

 PHENOL RED 

 DIODRAST IODINE 



CONCENTRATION 



PER CENT 



FIGURE 3 



Figure 3. Diagrammatic summary of excretion of various types of compounds by 

 the human kidney. The quantitative relations are fully described in the text. 



completely filterable from plasma, and their low clearances 

 must be attributed to tubular reabsorption. The urea clear- 

 ance (plasma) averages about 70 cc, inuhn, 125 cc, crea- 

 tinine, 175 cc, phenol red, 400 cc, and diodrast, 737 cc per 

 minute. From what has been said above, we may infer that 

 the various values of these clearances reveal differences in the 

 efficiency with which the respective substances are excreted, 

 these differences being due to differences in the mechanism 

 of excretion. Accepting the presumption that the inulin 

 clearance is equal to the rate of glomerular filtration, it fol- 

 lows that substances, such as Na, K, Cl, amino acids, glucose 

 and vitamin C, the clearances of which are less than the inulin 

 clearance, must be reabsorbed by the tubules (providing of 

 course that they are filterable through the glomeruli), while 

 substances such as creatinine, phenol red, iopax, hippuran and 



