310 ANATOMY FOR NURSES [Chap. XVI 



system, but the enzymes contained in the Hver and the internal 

 secretion of the pancreas, and some of the ductless glands play a 

 very important part. 



Function of carbohydrates. — The oxidation of glucose serves 

 the following purposes: (1) It furnishes the main if not the only 

 source of energy for muscular work, and for all the nutritive 

 processes of the body. (2) It furnishes an important part of 

 the heat needed to maintain the body temperature. (3) It pre- 

 vents oxidation of the body tissues, because it constitutes a re- 

 serve fund that is the first to be drawn upon in time of need. 

 (4) An excess of carbohydrates over and above what can be 

 stored as glycogen in the liver and tissues is converted into adipose 

 tissue. 



Waste products of carbohydrate metabolism. — The waste 

 products resulting from the oxidation of glucose are carbon 

 dioxide (CO2) and water (H2O). This process is thought to be 

 comparable to the fermentation of sugar outside the body, and 

 the same substances are formed, viz. alcohol, acids, carbon 

 dioxide, and water. 



METABOLISM OF PROTEINS 



The substances resulting from the digestion of proteins, i.e. 

 peptones, polypeptids, and amino-acids are not found in the 

 blood to any extent, because during the passage of these sub- 

 stances through the intestinal walls they are changed to serum- 

 albumin and serum-globulin. The tissues take these substances 

 from the blood and, by a process that is not well understood, 

 convert them into protein material of the kind found in any 

 particular tissue. In this way broken-down tissue is replaced 

 and new tissue is formed. The protein substances absorbed are 

 usually in excess of what is needed for repair and tissue building. 

 This excess is acted upon by the liver, and the protein molecule 

 is split up into two parts. One part is known as the ammonia 

 molecule, and contains hydrogen and nitrogen. This is subse- 

 quently converted into urea and similar substances, which are 

 carried by the blood to the kidneys and excreted in the urine- 

 The second part may be either oxidized directly, or built up into 

 carbohydrates and fats which eventually become oxidized, and in 

 either case heat and energy are liberated. 



