H58 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



CORT 



--PAP D 



fig. I. Anatomical distribution of nephron types in the hu- 

 man kidney. CORT.: cortex; O.ST.: outer stripe or band; 

 O.Z.: outer zone of medulla; INST.: inner stripe or band; 

 MED.: medulla; IN.Z. : inner zone of medulla; PAP.D.: pap- 

 illary duct. [After Peter (245).] 



new importance as the vascular counterpart of the 

 countercurrent system of the nephrons. Longley et al. 

 (191) look upon the vasa recta as retia mirabilia 

 conjugata (similar to the retia mirabilia of the swim 

 bladder of fishes), especially endowed to function as a 

 countercurrent multiplier system. Recent studies 

 (166, 309) have shown that the flow of blood through 

 these vessels appears to be significantly slower than 

 through the cortical circulation, apparently a func- 

 tional adaptation to the optimal operation of the 

 countercurrent mechanism. 



The question of the possible role of the phenomenon 

 of the autoregulation of the renal circulation in the 

 countercurrent system has been raised. Speculatively, 

 it would appear undesirable for rapid fluctuations in 

 blood flow to occur through the zone of hypertonicity, 

 and the over-all constancy of renal blood flow may 

 thus be an adaptation to insure stability in this system. 



This article will include largely the developments 

 in renal circulatory physiology since Homer Smith's 

 review in 1940 of The Physiology of Renal Circulation 

 (286). This era has seen the ascendancy of the 

 clearance method for measurement of renal blood 

 flow, the waxing and waning of the Trueta juxta- 

 medullary shunt mechanism, the development of a 

 growing interest in the mechanism of renal circulatory 

 autonomy, and the unfolding of the countercurrent 

 hypothesis of kidney function with important implica- 

 tions for the renal circulation. 



FUNCTIONAL ARCHITECTURE OF THE 

 RENAL CIRCULATION 



Limitation of space precludes the consideration of 

 the anatomy of the renal circulation on the broad 

 comparative basis that it warrants. Rather, major 

 emphasis will be placed on the salient features of 

 circulation in the dog, the species in which a significant 

 proportion of the functional studies have been made, 

 with appropriate references to other species, especially 

 human, when needed for full development of a given 

 topic. 



Arterial System 



Major distribution of the renal artery in the dog is 

 shown in figure 2 [from plastic injection corrosion 

 studies of von Kiigelgen et al. (322)]. Figure 3 shows 

 division of the interlobar artery into primary, 

 secondary, and tertiary arcuate arteries, from which 

 spring the interlobular arteries. The afferent arterioles 

 usually supply only one glomerulus, but rarely may 

 branch to supply 2 to 4 glomeruli with a total of 

 200,000 per kidney. This is compared to estimates 

 ranging from 600,000 to 1,700,000 in each human 

 kidney (213, 216, 318). 



specialized arterial circuits. Spanner (290, 291), 

 Trueta et al. (311), Baker (6), and von Ki'igelen & 

 Passarge (323) have found peculiarly coiled vessels 

 (which arise from the interlobar arteries) in the renal 

 sinus of dog, cat, and human. These spiral vessels, 



