78 



HUMAN PHYSIOLOGY. 



FIG. 10. 



of. small orifices which are the beginnings of the uriniferous tubules. 



From this point the tubules pass outward in a straight but somewhat 

 diverging manner toward the cortex, giving off at 

 acute angles a number of branches (Fig. 10). From 

 the apex to the base of the pyramids they are 

 known as the tubules of Bellini. In the cortical 

 portion of the kidney each tubule becomes en- 

 larged and twisted, and after pursuing an extremely 

 convoluted course, turns backward into the medul- 

 lary portion for some distance, forming the descend- 

 ing limb of Henle's loop; it then turns upon itself, 

 forming the ascending limb of the loop, reenters 

 the cortex, again expands, and finally terminates in 

 a spherical enlargement known as Mailer's or Bow- 

 man's capsule. Within this capsule is contained a 

 small tuft of blood vessels constituting the glomerulus 

 or Malpighian corpuscle. 



Structure of the Tubules. Each tubule consists 

 of a basement membrane lined by epithelial cells 

 throughout its entire exetnt. The tubule and its 

 contained epithelium vary in shape and size in different 

 parts of its course. The termination of the convoluted 



. tube consists of a little sac or capsule, which is ovoidal 

 Diagrammatic exposi- 

 tion of the method in shape and measures about ^^ of an inch in size. 



rouft'ilbes^unufro" This capsule is lined by a layer of flattened epithelial 



form primitive cones ce u s w hich is also reflected over the surface of the 



lyson.) after L,ud- 



ivig. glomerulus. During the periods of secretory activity, 



the blood vessels of the glomerulus become filled with 

 blood, so that the cavity of the sac is almost obliterated; after secretory 

 activity the blood vessels contract and the sac cavity becomes enlarged. 

 In that portion of the tubule lying between the capsule and Henle's loop 

 the epithelial cells are cuboidal in shape ; in Henle's loop they are flattened, 

 while in the remainder of the tubule they are cuboidal and columnar. 



Blood vessels of the Kidney. The renal artery is of large size and 

 enters the organ at the hilum; it divides into several large branches, which 

 penetrate the substance of the kidney, between the pyramids, at the base 

 of which they form an anastomosing plexus, which completely surrounds 

 them. From this plexus vessels follow the straight tubes toward the apex, 

 while others, entering the cortical portion, divide into small twigs which 



