CHAPTER XVII 

 THE REMOVAL OF WASTE PRODUCTS 



As we have seen, the volatile waste products of the 

 body's activity are constantly removed from the blood 

 by the air in the lungs. The non- volatile waste products 

 which are in solution in the blood cannot, however, be 

 got rid of in this way, since they are incapable of pass- 

 ing from the blood to the air. To dispose of them, 

 special organs have been developed, notably the kidneys. 



Kidneys. The kidneys are two rounded bodies, one 

 of which lies on each side of the spine in the upper part 

 of the abdominal cavity just under the lowest ribs. In 

 size, they are nearly five inches long, two and three- 

 quarters inches wide and one and three-quarters inches 

 thick, and weigh about four ounces each. They are red- 

 dish-brown in color, of firm consistency and covered with 

 a smooth membrane. 



Blood supply. Each kidney contains two complete 

 systems of tubes. One is made up of the branching 

 arteries, capillaries and veins, which carry the arterial 

 blood from the aorta into, through and out of the kid- 

 neys. On leaving the kidneys, the blood enters the large 

 abdominal vein which returns it directly to the heart. 

 Thus a part of the arterial blood is constantly passing 

 through them. 



Structure. The other system of tubes consists of a 

 very complex meshwork called renal tubules, which 

 begin as tiny cups surrounding tufts of capillaries. 



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