DIGESTION IN THE INTESTINES 



357 



occurring in disease of those parts. The efferent impulses are carried by the 

 phrenics and other spinal nerves and by the vagus. 



DIGESTION IN THE INTESTINES. 



The food that enters the small intestine has already been subjected to two 

 digestive enzymes. The ptyalin of the saliva and the pepsin of the gastric 

 juice together with the mechanical processes involved have reduced the food 

 to a pulpy mass, the chyme. This peptonized/00d contains most of the total 

 quantity of food eaten, little having been absorbed, as we shall see later, but 

 much of the starch has been changed to soluble maltose and dextrose and 

 the protein to albumoses and peptones. The discharge from the stomach 

 through the pyloric valve to the duodenum has been going on through three 



FIG. 264. FIG. 265. 



FIG. 264. Piece of Small Intestine (previously distended and hardened by alcohol), 

 Laid open to Show the Normal Position of the Valvulae Conniventes. 



FIG. 265. Section of the Pancreas of a Dog During Digestion, a, Alveoli lined with 

 cells, the outer zone of which is well stained with hematoxylin; d, intermediary duct lined 

 with squamous epithelium. X 350. (Klein and Noble Smith.) 



or four hours on an average for each full meal. This stream of food passing 

 down the small intestine, slowly because of the valvulae conniventes, meets 

 a number of secretions which contain enzymes which act on each of the three 

 great food principles, proteins, fats, and carbohydrates. These secretions 

 are the pancreatic fluid, the succus entericus, and the bile. 



The Pancreas. The pancreas is situated within the curve formed 

 by the duodenum, and its main duct opens into that part of the small intes- 

 tine through a duct common to it and to the liver and about two and a half 

 inches from the pylorus. 



The pancreas bears some resemblance in structure to the salivary glands. 

 Its capsule and septa, as well as the blood vessels and lymphatics, are simi- 



