50 PHYSIOLOGY FOR NURSES 



The fat splitting enzyme, lipase, or steapsin, is formed 

 by the pancreas. 



Proteolytic ferments are pepsin, formed in the glands 

 of the stomach and acting only in the presence of an 

 acid, and trypsin, formed by the pancreas and acting in 

 an alkaline medium. 



Besides these well-known ferments, the glands in the 

 wall of the small intestines furnish various enzymes 

 which act upon the partly digested food poured into the 

 intestinal canal by the stomach. Their action is not so 

 well understood as is that of the secretions of the stom- 

 ach and pancreas. 



Before considering the action of the digestive fer- 

 ments, an account of the mechanics of the alimentary 

 canal will be given. 



The simplest form of feeding and digesting is in an 

 unicellular organ, a single cell of protoplasm, which 

 wraps itself around its food and becomes, in its entirety, 

 a chewing, swallowing, digesting, absorbing and dis- 

 charging organism. In man, and the higher animals, af- 

 ter food has been procured, the successive steps are 

 chewing (mastication), swallowing (deglutition), and di- 

 gestion. The organs concerned are the mouth, contain- 

 ing the teeth, tongue, and salivary gland; the pharynx 

 and esophagus, the swallowing organs ; the stomach and 

 intestines which are the digesting, absorbing and evacu- 

 ating organs. 



Food is held between the grinding teeth by the mus- 

 cles of the cheek (chiefly the buccinator) on the outside 

 and the tongue between the teeth. Here it is not only 

 thoroughly crushed, but is mixed with the saliva which 

 begins the digestion of starchy food. When this proc- 

 ess is completed, the larynx is pressed up under the hyoid 

 bone and the base of the tongue, the top of which organ, 



