DIGESTION AND ABSORPTION 



309 



vessels, while inside of these, occupying the core of the villus, are 

 found spaces which, because of their white appearance after 

 absorption of fats, have been called lacteals. (See figure, page 207.) 

 Absorption of Foods. - Let us now attempt to find out exactly 

 how foods are passed from the intestines into the blood. Food 

 substances in solution may be soaked up as a sponge would take up 

 water, or they may pass by osmosis into the cells lining the villus. 

 These cells break down the peptones into 

 a substance that will pass into and be- 

 come part of the blood. Once within the 

 villus, the sugars and digested proteins 

 pass through tiny blood vessels into the 

 larger vessels comprising the portal cir- 

 culation. These pass through 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 sent to the heart, from there is pumped 

 to the lungs, from there returns to the 

 heart, and is 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 intestine as the 

 food passes on its course. The fats in 

 the form of soaps and fatty acids pass 

 into the space in the center of the villus. 

 Later they are changed into fats again, 

 probably in certain groups of gland cells 

 known as mesenteric glands, and eventually reach the blood by 

 way of the thoracic duct without passing through the liver. 



Large Intestine. The large intestine has somewhat the same struc- 

 ture as the small intestine, except that it lacks the villi and has a greater 

 diameter. Considerable absorption, however, takes place through its 

 walls as the mass of food and refuse material is slowly pushed along by 

 the muscles within its walls. 



Vermiform Appendix. - - At the point where the small intestine widens 

 to form the large intestine, a baglike pouch is formed. From one side of 



Diagram to show how the 

 nutrients reach the blood. 



