CHAPTER XXVII 

 METABOLISM 



Metabolism is a part of that complex series of processes grouped 

 together under the head of Nutrition. It embraces a consideration 

 of those changes taking place in the body other than those customarily 

 classified as secretion, digestion, excretion, etc. Metabolism may be de- 

 fined as all chemical and physical changes which occur in living matter 

 and which constitute the basis of the material phenomena of life. This 

 conception of metabolism holds for the simple individual cell of the 

 amoeba as well as for the complex mechanism of the human body. There 

 are two types of metabolism, one constructive, the other destructive. 

 The constructive metabolism is termed anabolism; the destructive 

 metabolism is termed catabolism. 

 Thus: 



1/r , , j. \ Anabolism (constructive metabolism). 

 Metabohsm , . 



[ Catabolism (destructive metabolism). 



In general we may say that the main bulk of the food-stuffs of the diet, 

 i.e., protein, fat and carbohydrate, is transformed in the gastro-in- 

 testinal tract and that the end-products of this transformation are 

 carried to the cells of the body and there built up by anabolic (synthetic) 

 processes into cell structure or stored as a reserve to be used as required. 

 All living cells undergo wear and tear in the course of their life cycle. 

 By catabolic (cleavage) processes therefore a portion of the living cell 

 substance or of the stored material is reduced to simpler fragments and 

 these are eliminated from the body after having yielded the bulk of 

 their energy in the form of heat or mechanical work. It is apparent, 

 therefore, that the chemical side of metabolism is closely associated 

 with the physical side. Each of the three types of food-stuffs (protein, 

 fat and carbohydrate) is concerned with the upkeep of the tissues and 

 with the liberation of energy. It is true, however, that the main 

 burden of the upkeep falls upon the proteins whereas the combustion of 

 fats and carbohydrates yields the major portion of the required energy. 

 The above facts are embraced in the following scheme: 



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