188 



The Vertebrate Organ Systems 



The outer cortex contains the thousands of individual kidney tubules; 

 the medulla contains the collecting tubules which receive the wastes 

 from the tubules of the cortex. The medulla is divided into cones, 

 the renal pyramids, which have their flattened bases against the cortex 

 and their apices projecting into a cavity, the sinus. The apices of the 

 pyramids contain the microscopic openings of the collecting tubules, 

 and are known as papillae. In cats and rats there is but a single papilla 

 while in man there are approximately twelve. 



The sinus is partially surrounded by the expanded anterior end 

 of the ureter, the pelvis. The sinus is nearly filled with the projecting 

 papillae and blood vessels which enter and leave at the hilus. 



.DISTAL 



CONVOIUTED 



TUBULE 

 _PROXIMAL 



CONVOLUTED 



TUBULE 

 .BOWMAN'S 



CAPSULE 

 .GLOMERULUS 



.AFFERENT 

 ARTERIOLE 



.EFFERENT 

 ARTERIOLE 



.ASCENDING 

 TUBULE 



Fig. 56. — Diagram of Icidney tubule and associated blood vessels. 



The Kidney Tubule. — The nephrons or kidney tubules are the 

 structures which remove materials from the blood and initiate the whole 

 process of urine secretion. Each nephron consists of two distinct por- 

 tions : the coiled capillaries or glomerulus and the tubule itself. Each 

 tubule's blind end is expanded to surround partially the glomerulus. 

 This blind end is the Bowman's capsule, and is composed of thin epi- 

 thelial cells. From the Bowman's capsule, the tubule becomes much 

 convoluted and is known as the proximal convoluted portion. Beyond 

 this, the tubule descends toward the medulla as the descending tubule, 

 and then makes a sudden turn, the loop of Henle, before ascending as 

 the ascending tubule. A short distal convoluted portion is present be- 

 fore the tubule joins with others, forming a collecting tubule. The 



