THE RENAL CIRCULATION 



[465 



Capsule 



Cortex 



Outet zone 

 of medulla 



Inner zone 

 of medulla 



fig. 11. The vasa recta system of the kidney. (Courtesy of 

 A. A. Maximov & VV. Bloom, Textbook of Histology. Philadel- 

 phia: Saunders, 1957.) 



cortical efferents. The impression is definitely gained 

 that the arterioles supplying the medullary zone are 

 not low-resistance vessels as originally suggested by 

 Trueta, but appear to be sites that could offer con- 

 siderable resistance to blood flow, thus resulting in a 

 significant drop in pressure gradient. One would 

 anticipate on this basis that hydrostatic pressure in 

 the vasa recta system would be very low were it not 

 for the relatively high venous pressure found in the 

 arcuate veins. Gottschalk & Mylle (112) and Wirz 

 (347), by direct puncture of cortical peritubular 

 capillaries in the rat, found an average of ca. 1 6 mm 

 Hg (range: 14.0 to 20.0 mm Hg), which is well below 

 the oncotic pressure of the plasma protein when one 

 considers that glomerular filtration concentrates the 

 protein. If this applies to the vasa recta, it would be 

 favorable for optimal operation of the countercurrent 

 system. The water abstracted from the collecting 

 ducts moves into the vasa recta because of the gradient 

 of chemical potential established by the colloid os- 

 motic pressure of the plasma proteins. 



Direct connections from the arcuate arteries into 

 the medullary zone (arteriolae rectae verae) have 

 been found in dog and man (18, 54, 217, 221, 311) 

 but appear to be rare. Likewise, Ludwig's arterioles, 

 branches from the afferent arterioles in the cortico- 

 medullary zone passing directly into the medullary 

 peritubular capillaries, are very infrequent in the 

 dog, cat, and man. They are very rare (295) in the 

 rat kidney. Oliver (236) and More & Duff (217) did 

 not find them in normal human kidneys. 



Renal Lymphatic System 



A greater lymphatic system (cortical) exists, and 

 there is a lesser (medullary) system which follows the 



table I . Averaged Measurements in Microns of Cortical and Medullary Arterioles per Kidney 

 and the Total Volume in cm 3 of the Muscle Composing Their Walls 1 



Arteriole 



Afferent 

 Efferent 



Total Xo. 



I ,000,000 

 820,000 



Length per 

 Arteriole 



277 

 200 



Total Length 

 Cortex 



277,000,000 

 164,000,000 



External Diam. Luminal Diam. 



26 

 16 



13 



12 



Total Muscle 

 Vol. in cm 3 



O.II 



O.OI4 



Medulla 



Efferent 180,000 600 108,000,000 33 18 0.065 



1st brs.-3 540,000 400 216,000,000 24 14 0.064 



2nd brs.-6 1,080,000 300 324,000,000 15 9 0.04 



1 Specimen calculation such as was used to obtain the muscle volume given in the last column of the above table. 

 Afferent arteriole: w X 13 2 X 277,000,000 = 147,087,000,000 ^i 3 = total volume 



7r X 6.5 2 X 277,000,000 = 37,1 18,000,000 m 3 = lumen volume 



Total volume less lumen volume = 109,989,000,000 m 3 = 0.11 cm 3 [After Edwards (79).] 



