DIGESTION AND ABSORPTION 



3" 



water). This separation prepares it for the action of pepsin. 

 Hydrochloric acid. — This secretion establishes the acid 

 medium necessary for the action of pepsin and may dissolve 

 some of the mineral salts. 



The cardiac or fundic end of the stomach (fig. 156) acts 

 as a reservoir for the food as it leaves the oesophagus. Here 

 the food may remain for sometime while the starchy matter 



is further acted upon by 

 the salivary juice. 



In the pre-pyloric and 

 pyloric end digestion of 

 proteid is begun by the 

 gastric juice. This is the 

 second stage in digestion. 

 It results in a milky mass 

 called chyme, which in 

 part is ready for absorp- 

 tion and in part needs 

 further treatment. This 

 passes in small amounts 

 into the small intestine. 

 The small intestine and 

 the intestinal juices. — The 

 intestine is a very long 

 coiled tube held in place by a fold of the peritoneum 

 called the mesentery. The mesentery is fastened at the 

 back to the spinal column. 



The coats of the small intestine are similar to those of the 

 stomach. The inner surface of the small intestine is covered 

 with minute papillae or projections called villi (fig. 161). 

 These are filled with blood vessels and lymphatic vessels. 

 Between the villi are numerous minute pores. These are 

 openings of tiny glands that secrete intestinal juices. Other 

 digestive secretions found in the small intestine are the bile 

 and the pancreatic juice. 



Fig. 161. Mucous membrane of the 

 small intestine of the dog. A, artery; 

 B, vein; C, capillaries; D, lacteals; 

 E, glands of Lieberkuhn; Ep., epi- 

 thelial tissue. (After Cadiat.) 



