1066 



EXCRETION 



and these in turn into larger ones until about a dozen conical bundles have been 

 formed, each of which constitutes what is known as a pyramid. The pointed ex- 

 tremity or apex of each pyramid projects well into the pelvic cavity, subdividing 

 the latter into a number of recesses. The pelvis is in free communication with the 

 ureter of which it really forms its funnel-shaped upper expanse. 



The flattened epithelium of Bowman's 

 capsule is reflected over the tuft of capil- 

 laries. In the distal convoluted tube, 

 however, the lining consists of high and 

 markedly granular cells which exhibit a 

 peculiar brush-like outer margin and vesic- 

 ular formations. In the descending limb 

 of the loop of Henle, the cells are flat and 

 clear, while those of the ascending limb 

 are again higher and striated. These 

 changes in the character of this epithe- 

 lium are responsible for the relative nar- 

 rowness of the lumen of the ascending 

 limb. The cells of the proximal con- 

 voluted tubule again present a decided 

 fibrillated appearance. Those of the 

 collecting channels are cuboidal or colum- 

 nar in shape and quite clear. 



The arterial supply of the kidney is 

 derived from the renal artery. Its two 

 terminal branches break up into smaller 

 ones which pass at first directly outward 

 but bend at almost right angles as soon as 

 they have reached the junction between 

 the medulla and cortex. From these 

 arched transverse vessels arise the inter- 

 lobular arteries which are directed straight 

 toward the surface of the organ and give 

 off here and there transverse branches 

 which finally form the tufts of capillaries, 

 previously described as the Malpighian 

 corpuscles. Each glomerulus, therefore, 

 consists of an afferent vessel representing 

 one of these branches, and a much nar- 

 rower efferent vessel which, after leav- 

 ing this structure, ramifies extensively 

 between the different convoluted tubules. 

 This capillary network then gives rise to 

 the interlobular veins and these in turn to 

 the renal vein. The medulla derives its 

 blood-supply from straight arterioles 

 which arise from the transverse arterial 

 arches. These constitute the arterial 

 rectae. 



The nerves innervating the kidney are 

 derived from the suprarenal plexus and 

 follow the highway of the artery around 

 which they form a rather close network. This plexus is known as the renal 

 plexus. It contains afferent and efferent fibers which are chiefly concerned with 

 the activity of the blood-vessels, although it has been claimed that they are also 

 secretomotor in their function. Preganglionically these fibers are contained in 

 the greater and lesser splanchnic nerves. 



FIG. 524. DIAGRAMMATIC REPRESEN- 

 TATION OF THE BLOOD-SUPPLY AND COURSE 

 OF THE URINIFEROUS TUBULE. 



J, Interlobular blood-vessels derived 

 from arches between cortex and medulla; 

 G, glomemli; C, distal convoluted tubule; 

 D and A, descending and ascending 

 limbs of the loop of Henle; CT, collect- 

 ing tubule; P. papilla and pelvis of the 

 kidney. 



