INTESTINAL DIGESTION l6l 



Intestinal juice (succus entericus] completes the digestion of 

 proteins and sugar, also of starch. It is an alkaline fluid 

 secreted by the small glands of the intestine, namely the glands 

 of Brunner and the follicles of Lieberkuhn or intestinal glands. It 

 contains several enzymes, erepsin, maltase, invertase and others. 



By erepsin the continuation of protein digestion is carried on, 

 by maltase and invertase the maltose formed in the mouth from 

 starch is converted into dextrose. 



Pancreatic juice is an alkaline fluid secreted by the pancreas. 

 Its enzymes are several in number, the most important being 

 trypsin, amylopsin and steapsin. Trypsin completes the digestion 

 of proteins already begun in the stomach, carrying it still further 

 by splitting those peptones which were not absorbed, into amino- 

 acids. (Trypsin digestion is important.) 



Amylopsin (pancreatic diastase) acts like ptyalin (or salivary 

 diastase) converting starch into dextrose. The principal digestion 

 of starch is accomplished here. 



Steapsin is the fat-splitting enzyme. Fats are probably 

 freed from their connective tissue envelopes before reaching the 

 intestine, and the steapsin splits them up into fatty acids and 

 glycerine. These fatty acids combine with the alkali of the 

 intestinal fluids to form soaps, which in solution are absorbable. 

 (Also soaps can emulsify the fats which continue to arrive, that is, 

 divide them into fine particles which will be suspended in the 

 alkaline solution.) 



What becomes of the soaps? Some are absorbed as such, 

 some form an emulsion with other fats. An emulsion was long 

 believed to be the only form in which fat was absorbed, and this 

 is not yet disproven. At all events, fat still appears as a white 

 emulsion called chyle in the absorbing vessels of the small intestine. 



The third important constituent of intestinal fluid is bile. 

 This is an alkaline fluid which enters the duodenum with the 

 pancreatic juice by the opening at the bile papilla. 



When the chyme enters the duodenum, the acid which it contains causes 

 the opening of the valve of the common duct, and the bile flows into the 

 duodenum. As soon as the chyme is made alkaline (by bile and intestinal 

 fluid) the valve closes not to be again opened until another portion of acid 

 chyme is received from the stomach. 



The bile contains no digestive enzymes. 



