ABSORPTION OF FOOD 



379 



This fluid or lymph then passes into the lacteals and other lym- 

 phatics and eventually reaches the blood. 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, pumped to the lungs, returned 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. 



Large intestine. The large intestine has somewhat the same 

 structure 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 peristaltic movements of the muscles 

 within its walls. At the point where the small intestine widens 

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

 one side of this pouch is given off a small tube, usually from 

 one to eight inches long, closed at the lower end. This tube, the 

 rudiment of what is an important part of the food tube in the 

 lower vertebrates, is called the vermiform appendix. 



Practical Exercise 4. Summarize the different pathways by which food 

 reaches the heart and general circulation by filling in the following table : 



Foods 



Where Absorbed 



Form 



Adaptations for 



Paths to Heart 

































Constipation. In the large intestine live billions of several 

 species of bacteria which, on the whole, may be said to be useful 

 because they break down and decay the indigestible parts of 

 the food we have eaten. But these same bacteria in their life 

 processes make and give off toxins. These substances are easily 



