THE URIXARY SYSTEM 



331 



Medullary ray in cor 

 tex 



Location in kidney Portion of tubule Epithelium 



Arched (passing from Rather clear cuboidal cells, 

 labyrinth to ray) 

 Part of ascending Cuboidal, granular, regular, 

 arm of Henle's 

 loop 

 Collecting tubule... Cuboidal or columnar, clear; 



varying in height with diameter 

 of tubule. 



Descending arni of Clear flat cells with bulging 

 Henle's loop nuclei. 



Henle's loop Usually like descending, rarely 



like ascending arm. 

 \ Part of ascending Cuboidal, granular, 

 arm of Henle's loop 

 Collecting tubule. . . Cuboidal or columnar, clear; 



varying in height with di- 

 ameter of tubule. 



Papilla Ducts of Bellini Clear, cuboidal or columnar 



cells according to diameter of 

 tubule. 



Medulla. 



The epithelium of the uriniferous tubule rests upon an apparently 

 structureless basement membrane. Rlihle describes the basement 

 membrane as consisting of delicate longitudinal and circular connec- 

 tive-tissue fibrils. He regards the fibrils as merely a more regular 

 arrangement of the interstitial connective tissue. According to 

 Riihle the epithelium simply rests upon the basement membrane, 

 being in no way connected with it. In the cortex the tubules are 

 closely packed and the amount of interstitial connective tissue is 

 extremely small. In the medulla the connective tissue is more 

 abundant. 



Of the function of the different parts of the uriniferous tubule our 

 knowledge is extremely limited. The water of the urine is secreted 

 in the ]\Ialpighian body, some specific action of the cells covering the 

 glomerulus, allowing the water, normally free from albumen, to pass 

 from the capillaries into the lumen of the tubule. The urinary solids 

 are secreted mainly or wholly by the cells of the convoluted tubules 

 and of the ascending arm of Henle's loop. 



Blood-vessels (diagram, Fig. 230). — The blood supply to the 

 kidney is rich and the blood-vessels come into intimate relations with 

 the tubules. The renal artery enters the kidney at the hilum, and 



