CHAPTER IX 

 DIGESTION IN THE INTESTINE 



General. Digestion in the mouth and stomach, although val- 

 uable in beginning the breaking down of the foodstuffs, does not 

 fit the greater part of the food for utilization by the body. The 

 final, and by far the most extensive portion of the task falls to 

 the intestine. 



When the acid chyme passes into the duodenum, or upper part 

 of the small intestine it becomes mixed with alkaline digestive 

 juices. Since pepsin is very sensitive to alkali, when this occurs 

 the peptic digestion stops. We now know, however, that the 

 contents of the small intestine may remain acid or neutral for 

 some time. The digestive activity of pepsin may thus continue 

 for a time after the chyme has left the stomach. 



There are three important digestive juices secreted into the 

 intestine, the pancreatic juice, the bile, and the succus entericus 

 or intestinal juice. The methods employed in studying digestion 

 in the intestine are in the main similar to those used for gastric 

 digestion, such as the preparation of fistulas or openings into 

 the intestine, removal of duodenal contents by means of a tube 

 passed down the esophagus and through the stomach, and 

 various other devices. 



Pancreatic Juice 



General. The pancreatic juice, or "external secretion" of 

 the pancreas, is produced by this gland, which lies along the 

 duodenum or close to it, and empties its secretion by two 

 main ducts and sometimes also smaller ones. The opening 

 of the pancreatic duct in man lies 9-10 cm. below the 

 pylorus. The amount of juice secreted varies with the 

 nature of the food. It has been estimated to average 500-800 



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