370 



EXCRETIOIT 



The entire length of the tube, its branches and capsules, 

 is lined with epithelial gland cells. The relation of these 

 parts is shown in Figure 172. Into each capsule enters a 

 tiny branch of the renal artery and there brealcs up into 

 a twisted knot of capillaries called a glomerulus which 



Fig. 171 — A Malpigbian capsule; 

 V. a, small branch of renal 

 artery breaking up in the glom- 

 erulus (f/./) into capillaries, 

 which in turn unite into the 

 renal vein (I'.e); -:, tubule; «, 

 epithelium over the glomeru- 

 lus ; &, epithelium lining the 

 capsule. 



Fig. 172 — Relation of parts in kid- 

 ney; a, artery; v, vein; c, capil- 

 laries about the tubule; g, glom- 

 erulus; t, tubule. 



nearly fills the capsule. These capillaries pour their con- 

 tents into a tiny vein, which, after leaving the capsule, 

 breaks up again in a network about the walls of the urinif- 

 erous tubules. This network fuses again into a single tube 

 which connects with the renal vein. 



Excretory action of the kidney. — The cells which line 

 the capsules and upper parts of the tubules are true gland 

 or secreting cells. Those in the lower part of the tubule 

 are purely for protection. The cells of the capsule secrete 

 only water and inorganic salts which they receive from the 



