GASTRIC DIGESTION 277 



esopahgus, which continues this muscular wave 

 (peristaltic wave). Some physiologists say that the 

 food passes through the pharynx and esophagus due 

 to a rise in pressure. Food as it passes into the 

 pharynx would enter the nasal cavities and larynx, 

 but the former cavities are closed by the action of 

 the tensor palate and levator palati muscles which 

 contract and draw upward and backward the palate 

 until it meets the posterior wall of the pharynx. The 

 larynx is closed from the food, for just at the time of 

 or before deglutition there is a temporary suspension 

 of inspiration, and the larynx is drawn up under the 

 base of the tongue and the opening to it closed by 

 the epiglottis falling downward and backward, pre- 

 venting food from entering the larynx. 



Gastric Digestion. The digestion of the food on 

 reaching the stomach is a further step in its gradual 

 preparation into a more liquid or semiliquid form to 

 enable the capillaries and lymph vessels within the 

 villi of the small intestines to absorb it after being 

 acted upon by the intestinal and pancreatic juices in 

 the small intestines. 



The walls of the mucous membrane of the stomach 

 between the periods of active digestion are being 

 bathed with an alkaline secretion derived from the 

 glands in its wall. This secretion of the gastric juice 

 has been produced reflexly by psychic influences, such 

 as the sight of food, and is also due to an irritation 

 of the mucous membrane produced by the presence 

 of food in the stomach. After digestion has com- 

 menced ' this secretion is profuse. The bloodvessels 

 of the mucous membrane become congested and the 

 glands show activity. The perpetual secretion of 

 gastric juice is supposed to be due to some chemic 

 change taking place, the resultant substance acting 

 as a specific stimulant to the cells of the glands. 



When food passes through the cardiac orifice due 

 to the peristaltic waves and pressure within the esoph- 



