CHAPTER X 

 ABSORPTION 



General. In the preceding chapters we have followed the 

 disintegration of the various foodstuffs in the different regions 

 of the alimentary canal. By the combined or successive action 

 of the digestive enzymes and other agents the widely varying 

 carbohydrates, fats and proteins of the food are broken down 

 into their simple building stones, monosaccharides, fatty acids 

 and glycerine, and amino acids. Thus from the complex foods 

 a mixture of simple substances is obtained. This mixture may 

 vary from time to time in the relative amounts of the different 

 building stones it contains, but the kinds of material it contains 

 are fairly uniform. In a strict sense the digestion products are 

 not yet in the body however. The alimentary canal is nothing 

 more nor less than a tube or corridor which passes through the 

 body. Through this corridor a great variety of materials is 

 made to pass. These materials are torn to pieces, and from the 

 resulting simpler substances the ever ready cells of the walls of 

 the alimentary canal select and take up certain substances. This 

 process is called absorption. As a matter of fact it has been 

 much debated whether absorption is merely a physical diffusion 

 of material through the walls of the alimentary tract, or whether 

 it involves the activities of the cells making up the intestinal 

 walls. Undoubtedly both of these factors come into play. 



Practically no absorption takes place in the mouth, and but 

 little in the stomach. There is some evidence that salts, mono- 

 saccharides and certain other substances may be absorbed to 

 some extent from the stomach if they are present in high con- 

 centration, but this is of little importance normally. 



The largest part of the absorption takes place in the small 

 intestine. The surface area of the intestine is greatly increased 



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