CHAPTER XX 

 METABOLISM 



Exercise promotes 



good metabolism. 



What is metabolism f How are the food nutrients used in the body? 



Metabolism is the term usually applied to all the processes which 

 are concerned in the building up and breaking down of the proto- 

 plasm in an organism. In short, it is the sum total of all the physi- 

 cal and chemical changes by which the protoplasm utilizes food, 

 releases .energy, and eliminates waste products in order to maintain, 

 repair, and produce more protoplasm. The processes of absorp- 

 tion, assimilation, respiration, and excretion are phases of metab- 

 olism, while digestion may be called a secondary process which 

 makes possible the primary activity of absorption. If the process 

 of metabolism is that of synthesis or building up, it is called an- 

 abolism, but if the process is one of tearing down, it is katabolism. 

 When the building up of protoplasm is greater than the breaking 

 down, growth takes place. 



No one function of the body can be discussed without referring 

 to one or all of the others because many of the functions take place 

 at the same time. During the anabolic process of assimilation, the 

 katabolic process of oxidation is also being carried on in order to 

 release enough energy for the assimilation and growth processes. 

 Before oxidation is possible, the digestion of the food must take 

 place. In fact, the process of metabolism involves all the physi- 

 ological functions of the body as well as the special activities that 



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