62 PHYSIOLOGY FOR NURSES 



lars: It can act in neutral, slightly acid or distinctly 

 alkaline solutions. 



Its effect on proteins is not only more powerful but 

 more rapid than that of pepsin. 



It breaks up the protein molecule more completely. 

 The joint action of trypsin and pepsin changes the com- 

 plex structure of the many kinds of protein into simple 

 bodies of the ammo-acid type more soluble than the 

 original form and prepares them for the action of erep- 

 sin (the protein enzyme of the intestinal juice) which 

 breaks up the products of peptic and tryptic digestion 

 into such simple forms that the human body can use 

 them as building stones out of which its own peculiar 

 form of proteins can be constructed. 



Amylase acts upon starches in the same way as 

 ptyalin, converting them into maltose and achroodex- 

 trin, a preparatory step to their final conversion into 

 dextrose by the maltose of the intestinal juice. This 

 digestion is completed by the time the food gets to the 

 ileocecal valve. 



Lipase or Steapsin is the first of the fat splitting fer- 

 ments. This ferment splits fats into glycerin and a 

 fatty acid and the latter combines with some of the salts 

 present to form a soap which is used to hold the fats in 

 an emulsion, in which form they are more readily acted 

 on by the lipase. This is the only ferment which seems 

 to have the power of acting in either direction; i.e., it 

 can either split fats or it can take the component parts 

 (glycerin and fatty acid) and combine them to form 

 fat. Lipase acts best in the presence of bile. 



Succus entericus, intestinal juice is secreted by the 

 tubular glands, crypts of Lieberkiihn, Avhich line the 

 intestinal canal. It seems to act only on starchy foods ; 

 but there are several enzymes in the juice which can 



