310 



THE ANIMALS AND MAN 



the peritoneal membrane and lined by a mucous membrane. 

 A submucous membrane lies between the muscular coats 

 and the mucous coat or epithehum. The large blood 

 vessels of the stomach lie in the peritoneum and send capil- 

 laries into the submucous coat. The mucous coat is smooth 

 when the walls of the stomach are distended, but wrinkled 

 when the stomach is empty and its walls collapsed. 



The stomach narrows at its lower or pyloric end and opens 

 into the small intestine (fig. 156). 



Glands. — The mucous lining 

 is covered with minute shallow 

 pits, the openings of the 

 gastric glands. The glands fur- 

 nish certain enzymes, pepsin 

 and rennin, all of which aid 

 in digestion. The -pyloric glands 

 (fig. 160), which furnish pepsin 

 only, lie in the pyloric end of 

 the stomach. The fundus 

 glands in the cardiac part of 

 the stomach, are formed of sev- 

 eral kinds of cells, and furnish 

 pepsin, rennin and hydrochloric 

 acid. 



The gastric juice containing 

 these enzymes acts in an acid 

 medium upon proteid food, while the ptyalin of the 

 salivary juice acts in an alkaline medium and upon carbo- 

 hydrates. 



The presence of food or food accessories in the stomach 

 stimulates the flow of gastric juice. 



Pepsin. — This enzyme changes proteid into a soluble form 

 called peptone. It acts at a rather high temperature. 



Rennin. — ^This enzyme acts upon milk, causing it to coagu- 

 late or separate into curds (the proteid part) and whey (mostly 



Fig. 160. Section of pyloric 

 glands from human stomach. 

 a, mouth of gland leading into 

 a long wide duct (6), into 

 which open the terminal divi- 

 sions; c, connective tissue of 

 mucosa. (After Piersoe.) 



