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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



CORTEX 



fig. 17. Distribution of osmotic con- 

 stituents in tubules and vasa recta sys- 

 tem of rats, indicating sites of active 

 and passive sodium, urea, and water 

 transport. The numbers represent hypo- 

 thetical osmolarity values. No quanti- 

 tative significance is to be attached to 

 the number of arrows and only net 

 movements are indicated. [After 

 Gottschalk & Mylle (113).] 



OUTER ZONE 

 OF MEDULLA 



fig. 18. Role of ADH in urine concentra- 

 tion and dilution in the countercurrent system. 

 In the concentrating kidney, ADH acts in a 

 permissive manner to facilitate water removal 

 from the distal convoluted tubule and collect- 

 ing tubule (white arrows) into the zone of hyper- 

 osmolarity. (Active sodium transport indicated 

 by heavy black arrows.) Water and sodium ex- 

 changes in the vasa recta system are indicated 

 as passive processes. The question mark at the 

 descending limb of the loop of Henle indicates 

 uncertainty as to the mechanism which initiates 

 the countercurrent exchange. [After Wirz 

 (349)-] 



renal blood flow (240), because plasma stripping in 

 the interlobular arteries should lead to progressive 

 hemoconcentration. The hemoglobin content of the 

 cortical capillaries was found to be below that of the 

 arterial blood hemoglobin, as measured by oximeter 

 techniques (165). Emery et al. stoutly support the 

 hypothesis by attributing the low hematocrit to axial 

 streaming of cells in the many small vessels of the 

 outer cortex. How this would fit into a concept of 

 autoregulation by changes created in blood viscosity, 

 and thus changes in vascular resistance (240), be- 

 comes difficult to envision. The somewhat higher 



values in the inner cortex and outer medulla may 

 reflect the hematocrit of larger vessels in this region. 



Although Emery et al. believe that the low medul- 

 lary hematocrit is further evidence of plasma strip- 

 ping, it could be equally well explained by escape of 

 labeled protein from the vasa recta into the inter- 

 stitial spaces, a view supported by Swann et al. (303). 



In dogs, autoradiographs appear to show a higher 

 concentration of I 131 -labeled albumin in the renal 

 papilla than in other regions of the kidney (174). 

 If a mechanism were to operate here to concentrate 

 plasma albumin above normal levels, this could lead 



