376 HOW FOOD IS PREPARED FOR BODY USE 



glycogen. 1 Glycogen is stored in the liver until such a time as a 

 food is needed that can be quickly oxidized ; then it is changed 

 to sugar and carried off by the blood to the tissue which requires 

 it, and there used for this purpose. Glycogen is also stored in 

 the muscles, where • it is oxidized to release energy when the 

 muscles are exercised. 



Self-Testing Exercise 



The liver stores (1), which is later changed into (2) 



when the tissues need it. The bile is secreted by the (3). 



It is a (4) (5) from the blood and it probably 



(6) in the absorption of (7) . The liver contains 



about (8) (9) of all the blood in the body. The 



bile (10) the -(H) movements of the intestine. 



PROBLEM vH. HOW ARE FOODS ABSORBED AND HOW DO 

 THEY GET INTO THE BLOOD? 



Laboratory Exercise. How is the surface of the digestive tube 

 increased ? 



Study the structure of tripe (stomach wall of a ruminant) and the 

 microscopic slide of a cross section of the small intestine. Remember 

 that the chief function of the small intestine is to get food into the 

 blood. 



Make a tube of paper having a diameter of one inch. Then try to 

 make a tube having the same diameter but having a fluted wall. 

 Which takes more paper? Which would present more surface? 

 Study the diagram of a villus. How is it fitted to be an absorbing 

 organ? 



Structure of the small intestine. The small intestine in man 

 is a slender tube nearly twenty feet in length and about one inch 

 in diameter. As one of the chief functions of the small intestine 

 is that of absorption, we must look for adaptations which increase 

 the absorbing surface of the tube. This end is gained in part 

 by the inner surface of the tube being thrown into transverse 

 folds which not only retard the rapidity with which food passes 

 down the intestine, but also give more absorbing surface. 



1 It is known that glycogen may also be formed in the body from protein, and 

 possibly from fatty foods. 



