DIGESTION AND ABSORPTION 187 



Intestines. — The acid condition of the food mass (chyme) 

 regulates the passage of the mass through the pylorus, the 

 opening from the stomach to the small intestine, the first twelve 

 inches of which is known as the duodenum. In the duodenum, a 

 few inches from the pylorus, the duct of Wirzung, leading from 

 the pancreas, together with the common bile duct from the 

 gall bladder, unite in a common opening. Due to the action 

 of the free hydrochloric acid of the chyme food mass a hormone, 

 prosecretin, produced by the ceil walls of the small intestine, 

 yields another hormone, secretin, which is then conveyed by the 

 blood to the pancreas. In the pancreas the secretin stimulates 

 the flow of pancreatic juice, which then flows down the duct of 

 Wirzung, unites with the bile from the gall bladder and together 

 they enter the small intestine. The intestinal juice, succus 

 entericus, secreted by the cells of the sm^all intestine, also mixes 

 with the pancreatic juice and the bile, and the three act to- 

 gether in the complete intestinal digestion. These juices are 

 all alkaline and neutralize the acid reaction of the chyme. The 

 amylolytic enzyme, amylopsin, of the pancreatic juice hydrolyzes 

 any undigested starch or dextrin to maltose, and then by the 

 combined action of the three disaccharose-hydrolyzing enzymes, 

 sucrase, maltase and lactase, present in the intestinal juice, 

 all carbohydrate food is hydrolyzed to the final end products 

 viz. glucose, fructose and galactose. In this form the carbo- 

 hydrate food is absorbed through the intestinal wall into the 

 blood capillaries, and enters the portal vein where they may all 

 three be found. Glucose is, however, the chief one of the three. 

 The pancreatic juice contains the zymogen, trypsinogen, which 

 is activated by an enzyme, enterokinase, of the intestinal juice, 

 yielding the active enzyme, tr3'psin. Trypsin is a proteolytic 

 enzyme and hydrolyzes unchanged protein mostly to amino- 

 acids but yielding also polypeptides, peptones and proteoses. 

 Following this in its action on protein food the enzyme, erepsin, 

 of the intestinal juice acts upon the derived proteins (peptones, 

 proteoses and polypeptides) converting them all by hydrolysis 

 into amino-acids. While some absorption of digestion products 



