CHAPTER XLII. 



DIGESTION AND ABSORPTION IN THE STOMACH. 



The muscular mechanisms by means of which the stomach is 

 charged with food and in turn discharged, small portions at a time, 

 into the duodenum have been described. The present chapter deals 

 only with the chemical and mechanical changes in the food during 

 its stay in the stomach and the extent to which the products of 

 digestion are absorbed. 



The Gastric Glands. The tubular glands that permeate the 

 mucous membrane of the stomach throughout its entire extent differ 

 in their histological structure, and therefore doubtless in their secre- 

 tion, in different parts of the stomach. Two, sometimes three, kinds 

 of glands are distinguished, the pyloric, fundic (and cardiac). 

 Those in the pyloric part of the stomach (antrum pylori) are char- 

 acterized chiefly by the fact that in the secreting part of the tubule 

 only one type of gland cell is found, the chief or peptic cell, while in 

 the remainder of the stomach, but particularly in the middle or 

 prepyloric region the glands (fundic glands) are distinguished by the 

 presence of two types of cells, the chief or central cells and the 

 so-called parietal or border cells (Fig. 293). The third type, the 

 cardiac glands, is found around the cardia, but its area of distribu- 

 tion varies in different animals, and its histological characteristics 

 are not very definite.* There seems to be a general agreement that 

 the central cells furnish the digestive enzymes of the stomach 

 pepsin and rennin and the parietal cells the hydrochloric acid. 

 From a physiological standpoint it is important to remember that 

 the parietal cells are massed, as it were, in the glands of the middle 

 or prepyloric region of the stomach, that they are scanty in the 

 fundus, and absent in the pyloric region. This fact is indicated 

 to the eye by the deeper red or brownish color of the mucous 

 membrane in the prepyloric portion. Grutznerf called especial 

 attention to this relation, and in connection with the differences 

 in movements of these two parts of the stomach he suggests that 

 normally the bulk of the food toward the fundus becomes impreg- 

 nated first with pepsin; then, as it is slowly moved into the pre- 

 pyloric region, the acid constituent is added. The pyloric glands 

 are said (Heidenhain) to secrete an alkaline liquid containing 

 pepsin, and, according to Edkins and Starling, they form a sub- 

 stance which is capable of acting as a chemical excitant to the 



* See Haane, "Archiv f. Anatomie," 1905, 1. 



t Griitzner, "Archiv f. die gesammte Physiologic," 106, 463, 1905. 



768 



