298 



THE MAINTENANCE OF THE INDIVIDUAL 



the intestine are like tiny chemical laboratories. Carbohydrates in 

 the form of monosaccharides, or glucose (dextrose), are absorbed 

 through the epithelial cells lining the villi and reach the capillaries of 

 the circulatory system. Proteins in the form of amino acids likewise 

 reach the blood stream in this way. Glycerin and fatty acids are 

 absorbed by the epithelial cells, resynthesized in these minute chemical 

 laboratories into more complex fats, and are then passed on to the 

 lymph channels, ladeals, of the lymphatic system in the villi. This 



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Cells of 

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intestm-al 

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Diagram of intestinal villi and glands. Can you explain the part played by 

 the villi in absorbing digested " foods " ? 



fluid or lymph then passes into the other lymphatics, eventually reach- 

 ing the blood through the thoracic duct which enters the jugular vein 

 in the neck. On the other hand, simple sugars and amino acids pass 

 directly into the blood and reach the blood vessels which carry them 

 to the liver, where, as we have seen, sugar is taken from the blood 

 and stored as glycogen. From the liver the food within the blood is 

 carried to the heart and is then pumped to the tissues of the body. 

 A large amount of water and some salts are also absorbed through 

 the walls of the stomach and intestines. The greatest loss of water, 

 however, occurs in the large intestine. 



