CHAPTER 43 



The renal circulation 



EWALD E. SELKURT 



Department of Physiology, Indiana University 

 School of Medicine, Indianapolis, Indiana 



CHAPTER CONTENTS 



Functional Architecture of the Renal Circulation 



Arterial System 



Venous System 



Glomerular Circulation 



Juxtaglomerular Complex 



Blood Supply to the Medullary Zones 



Renal Lymphatic System 

 Nerve Supply to the Kidney : Anatomical Aspects 



Extrinsic Nerves 



Intrinsic Innervation 

 Distribution of Osmotic Constituents in the Kidney: The 



Countercurrent Hypothesis 

 Renal Blood Volume: The Intrarenal Hematocrit 

 Metabolic Aspects 



Oxygen Utilization 



Heat Production 

 Pressure Gradients in the Renal Vascular Circuit 



Pressure Gradients 



Critical Closure; Yield Pressure 



Intrarenal Pressure 

 Measurement of Renal Blood Flow 



Methods 



Critique of the Clearance Method 



Renal Blood Flow Values 

 Extrinsic Regulation of Renal Blood Flow 



Neurogenic Control 



Humoral Control; Pharmacologic Agents 

 Anatomy of the Renal Circulation 



History 



Mechanism of Autoregulation 

 Present Status of the Trueta Juxtamedullary Shunt 



Morphological Evidence 



Functional Evidence; Interpretations Based on Clearance 

 Rate 



Role of the Medullary Circulation in Diuresis and Anti- 

 diuresis 

 Response of Renal Blood Flow in Physiological Stress 



Exercise 



Posture and Orthostatic Hypotension 



Renal Hypoxia and Ischemia 



Hypercapnia and Acidosis 

 Hemorrhagic Hypotension and Shock 

 Concluding Remarks 



the introduction of the concept of the counter- 

 current osmotic multiplier system to the kidney by 

 Wirz el al. (345-349) as a means of explaining 

 urinary concentration and dilution has apparently 

 initiated a phase of re-evaluation of classical renal 

 functional concepts which promises to be far reaching 

 in scope. Recent critical reviews, while pointing out 

 gaps in our knowledge, have nevertheless opened up 

 exciting vistas and new pathways for research (169, 

 171, 289, 314)- The countercurrent concept rests 

 rather firmly on findings in the rat and hamster; 

 however, significant anatomical differences in the 

 kidneys of the dog and man require that this hypoth- 

 esis be intensively tested in these and other species. 

 Only about one-eighth of the nephrons of the human 

 kidney appear to have the long medullary loops of 

 Henle requisite for the mechanism (245). Most lie in 

 the cortex, and have straight, short, thin segments, or 

 indeed, none at all (fig. 1). The dog, however, has 

 long loops and long, thin medullary segments, yet 

 its kidneys are not remarkably different from those of 

 the human in concentrating power. 



The renal circulation has been found to play a 

 unique and important role in the composite picture of 

 the countercurrent mechanism. Knowledge of the 

 distribution of blood to the cortex and medulla has 

 assumed pre-eminent importance. Older ideas have 

 had to be revised. The vasa recta, considered originally 

 as a medullary shunt by Trueta et al. (311), assume 



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