94 Physiology of the Kidney 



If the renal plasma flow were reduced pari passti with the 

 renal parenchyma, as measured by diodrast-Tm, this plasma 

 flow would descend along the upper line. This is roughly the 

 case, but most of the subjects show a plasma flow per unit of 

 residual functional tissue which is markedly below the ex- 

 pected value. These subjects may be said to show a relative 

 or functional ischemia of the residual excretory tissue. The 

 frequency of this functional ischemia suggests that the renal 

 vascular bed is being occluded in advance of the destruction 

 of renal parenchyma, rather than that the progressive de- 

 struction of both vascular bed and parenchyma are proceed- 

 ing simultaneously. 



The interpretation of the course of events in the hyper- 

 tensive kidney presents many complexities and must proceed 

 cautiously; the data in Figure 7 appear at first sight to pre- 

 sent several contradictions, and in any case the measurement 

 of the total plasma flow, total filtration rate and total excre- 

 tory mass does not immediately throw light upon what is 

 going on in individual nephrons. But when we consider these 

 data in terms of the possible courses of events there emerge 

 several impressive consistencies. In the interests of brevity 

 we may attempt a further analysis of the data by hypothesis, 

 and by observing wherein these data are consistent with this 

 hypothesis. 



But first let us note what factors could in principle mod- 

 ify the plasma flow and filtration rate. On the one hand, the 

 plasma flow would tend to be decreased by systemic hypoten- 

 sion, or by constriction of either the afferent or efferent ar- 

 terioles. (Any arterial occlusion on the afferent side of the 

 glomeruli may be included in afferent constriction.) On 

 the other hand, the renal plasma flow would tend to be in- 



