102 HUMAN PHYSIOLOGY. 



GASTRIC DIGESTION. 



The Stomach. Immediately beyond the termination of the esopha- 

 gus the alimentary canal expands and forms a receptacle for the 

 temporary retention of the food. To this dilatation the term stomach 

 has been applied. This organ is somewhat pyriform in outline, and 

 occupies the upper part of the abdominal cavity. It is about 13 

 inches long, 5 deep, and 3^ wide, and has a capacity of about five 

 pints. It presents two orifices, the cardiac or esophageal, and the 

 pyloric ; two curvatures, the lesser and the greater. 



The left or cardiac end of the stomach is enlarged, and forms the 

 fundus ; the right end is much narrower, and forms the pylorus. The 

 stomach possesses three coats : 



1. The serous, or reflection of the peritoneum. 



2. The muscular, the fibers of which are arranged in a longitudinal, 

 a circular, and an oblique direction. At the pyloric end the 

 circular fibers increase in number and form a thick ring or band, 

 which is known as the sphincter of the pylorus. 



3. The mucous, which is somewhat larger than the muscular coat, and 

 in consequence is thrown into folds or rugae. The surface of the 

 mucous coat is covered by tall, narrow, columnar epithelium. 



Gastric Juice. During the period of time the food remains in the 

 stomach it is subjected to the disintegrating action of an acid fluid, 

 the gastric juice. This fluid, secreted from glands in the mucous 

 membrane, is thoroughly incorporated with the food in consequence 

 of the contractions of the muscular coat. The food is gradually 

 liquefied and reduced to a form which partly fits it for passage into 

 the small intestine and for absorption into the blood. Gastric juice, 

 when obtained in a pure state, is a clear, colorless fluid, decidedly acid 

 in reaction, with a specific gravity of 1005. It is composed of the 

 following ingredients : 



COMPOSITION OF GASTRIC JUICE. 



Water 994.404 



Hydrochloric acid 0.200 



Organic matter 3-195 



Inorganic salts 2.201 



