THE METABOLIC MACHINERY OF ANIMALS 295 



local constrictions occurring at points where the food masses lie. 

 Such contractions break up the food into a number of segments 

 enabling the enzymes to reach all parts. 



The Intestinal Glands. The partly digested food in the small 

 intestine comes in contact almost simultaneously with secretions from 

 the liver, pancreas, and intestinal glands. 



The Pancreas. As the acid chyme enters the duodenum it 

 activates some "prohormone," probably -prosecretin, which is first 

 absorbed into the capillaries of the blood vessels and then carried 

 throughout the body. Some secretin ultimately reaches the pancreas, 

 which is then stimulated to further activity causing the chemical 

 secretion of the pancreatic juice. The pancreas is one of the most 

 important digestive glands in the human body. It is anatomically 

 a rather diffuse structure resembling the salivary glands in form. 

 Its duct, joined with the bile duct from the liver, empties into the 

 small intestine a short distance below the pylorus near the juncture 

 of the duodenum and the ileum. 



The secretions of the pancreas or "stomach sweet bread" contain 

 three groups of enzymes, (1) amylopsin, (2) trypsin and some erepsin, 

 and (3) lipase, which act respectively upon carbohydrates, proteins, 

 and fats. The first, amylopsin, breaks down starches by hydrolysis 

 to double sugars, finally yielding the disaccharide maltose, and dextrin. 

 Maltose is further broken down by maltase into a monosaccharide, 

 glucose (dextrose), which may then be absorbed. 



Second, in order for absorption to take place in proteins they must 

 be broken down into their constituent arnino acids by the action of 

 at least trypsin and erepsin. Protein material reaches the first por- 

 tion of the small intestine, or duodenum, in the acid chyme which is 

 generally neutralized somewhat before the proteolytic enzymes do 

 their work. 



Third, fats, thus far unchanged in the process of digestion except to 

 be melted by the heat of the body, are then emulsified by the bile and 

 finally are hydrolyzed in the intestine by the action of lipase into 

 glycerol (glycerin), and also one or more fatty acids. These are 

 absorbed by the epithelial cells of the villi, resynthesized into more 

 complex fats, and passed into the lymph channels, or lacteals. 



Aside from the noteworthy office of "secretor of the pancreatic 

 juice," the pancreas has another important function. One might 

 say that it is one of the "board of directors" governing the li(>altli 

 of the body. When the sugar content of the blood becomes too high 



H. V. H. — 20 



