CHAPTER XLIII. 

 DIGESTION AND ABSORPTION IN THE INTESTINES. 



The food undergoes its most profound digestive changes in the 

 intestines, and here also the products of digestion are mainly ab- 

 sorbed. The intestinal digestion begins in the duodenum, and is largely 

 completed by the time that the food arrives at the ileocecal valve. 

 It is effected through the combined action of three secretions, the 

 pancreatic juice, the secretion from the intestinal glands (succus 

 entericus), and the bile. These secretions are mixed with the food 

 from the duodenum on, so that their action proceeds simultaneously. 

 For purposes of description it is necessary to speak of each more or 

 less separately. 



The Pancreas. The pancreas forms a long, narrow gland reach- 

 ing from the spleen to the curvature of the duodenum. Its main 

 duct in man (duct of Wirsung) opens into the duodenum, together 

 with the common bile-duct, about 8 to 10 cms. beyond the pylorus. 

 The points at which the duct or ducts of the pancreas enter the 

 intestine vary somewhat in different mammals. In the dog there are 

 two chief ducts, one opening, together with the bile-duct, about 3 to 

 5 cm. below the pylorus, while a second enters the duodenum some 

 3 to 5 cms. farther down. In rabbits the principal pancreatic duct 

 opens separately into the duodenum about 35 cms. below the opening 

 of the bile-duct. The pancreas is a compound tubular gland like 

 the salivary glands.' The cells lining the secreting portion of the 

 tubules, the alveoli, belong to the serous or albuminous type. They 

 are characterized by the fact that the outer portion of each cell is 

 composed of a clear, non-granular material which stains readily, 

 while the inner portion, the portion facing the lumen, contains 

 numerous granules. Histological study of the gland after active 

 secretion, as compared with the resting state, has shown very con- 

 clusively that these granules represent a preparatory material for 

 secretion. As the secretion proceeds the granules are dissolved 

 and discharged into the lumen, while during the periods of rest new 

 granules are formed by metabolic processes at the expense, appar- 

 ently, of the non-granular material in the basal portion of the cell. 

 (Heidenhain, Kiihne, Lea). The histological picture of secretion 

 is in general the same in this as in the salivary and gastric glands, 

 only somewhat more distinctly shown. On the supposition that the 

 granules constitute an antecedent material from which the enzymes 



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