30 Physiology of the Kidney 



tubule, by virtue of ischemia or local intracellular damage, is 

 incapable of function. This category would include only 

 patent nephrons which are connected with the collecting 

 ducts and which therefore serve as passive conduits to drain 

 glomerular filtrate out of the body. 



5. In the category of inert scarred tissue we would in- 

 clude not only fibrotic glomeruli and fragmented or necrotic 

 tubular tissue, but also anatomically intact nephrons which 

 are obstructed by casts of epithelium, albumin, etc., or which 

 are disconnected from the collecting ducts, so that function 

 is at least temporarily impossible. 



In the above schema the nephron is viewed as a unitary 

 structure with but a single function. This is of course not 

 true; the proximal tubule is probably concerned with the 

 reabsorption of sodium, chloride, glucose, vitamin C and 

 possibly other constituents of the glomerular filtrate, and 

 with the excretion of creatinine, phenol red, diodrast and 

 possibly other substances. The thin segment is perhaps 

 chiefly concerned with the hypertonic reabsorption of water, 

 the distal segment with the final adjustment of the urine in 

 respect to chloride, pH, HCOs, etc. But obviously we cannot 

 appraise all these functional activities at this time. Our 

 methods limit our examination to glomerular function, on 

 the one hand, and on the other to two functions of the proxi- 

 mal tubule: the excretion of diodrast and the reabsorption 

 of glucose. 



A priori it may be supposed that even in the healthy kid- 

 ney the number of normal active nephrons may be variable, 

 giving way to either inactive nephrons or aglomerular neph- 

 rons; and with greater confidence we can expect to discover 

 such transitions to occur in consequence of disease. 



Utilizing the methods I have discussed above, we can 



