DIGESTION OF FOOD: THE (ESOPHAGUS 



95 



the gastric juice. It takes some time, however, for the 

 swallowed food to become thoroughly mixed with the 

 gastric juice and therefore, for perhaps an hour after 

 reaching the stomach, the conversion of starch into sugar 

 continues. 



For a long time it was held that fat undergoes only melt- 

 ing and emulsification in the stomach; but more recent 

 studies show the presence, in a limited way, of a third fer- 

 ment, gastro-lipase, which changes fats into glycerin and 

 j fatty acids. Absorption of fats is now possible, but prob- 

 ; ably this does not occur till they have gone on into the in- 

 testinal division of the 

 '. alimentary canal. 



The Flow of the Gastric 

 Juice i Between meals, 

 when the stomach is 

 practically empty, its 

 walls are of a pale pink 

 color, and the lining is 

 merely moist; very little 

 secreting work is done by 

 the glands. But, on the 

 entrance of food, the 

 blood vessels in the 

 stomach walls expand, 

 and more blood flows 

 around the glands, the 

 cells of which begin a 

 copious secretion. Like 

 the case of the salivary 

 secretions, this response 

 of the blood vessels and 



glands is a reflex action, controlled by the central ner- 

 vous system. The actual contact of the mouth or stomach 



Spinai 

 'Cord 



FIG. 51. DIAGRAM 



Showing the method by which the stomach 

 receives its nerves from the brain and cord. 

 The nerves from the cord actually come 

 through the sympathetic system, not shown 

 in the figure. (Modified from Openchowski; 



