EXCRETION 



207 



glands and kidneys are usually regarded as the excretory 

 organs of man. These organs remove from the blood the 



wastes which have been excreted by the cells of the body. 

 The excretion from the living cells is one of tin* funda- 

 mental life processes of all plants and animals. This form 

 of excretion should not 

 be confused with the in- 

 digestible part of the 

 food which is not taken 

 up by the blood and 

 which passes out through 

 the large intestine as 

 fseces. 



The kidneys are two 

 bean-shaped organs lo- 

 cated in the abdominal 

 cavity, one on each side 

 of the "small" of the 

 back. Each is about 

 four inches long, two 

 and a half inches wide, 

 and half an inch thick. 

 The color is a dark red. 

 The kidney is made up of two' layers, the outside or 

 cortical, and the inside or medullar jf. Each layer is com- 

 posed of many small tubes (tubules') which open into an 

 area called the pelvis} the space within the kidney. The 

 pelvis continues into a duct (ureter), and from each 

 kidney the ureter passes into the bladder. A small duct 

 (urethra) connects the bladder with the exterior of the 

 body. 



Each tubule in the kidney is in dose relation with the 



Figure 220. — Section of Kidney. 



i The word pelvis is also used in referring t«> the hip bones, and it Is better 



to call the latter structure the bony pelvis. 



