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 cells and the so-called cover 

 or border cells (Fig. 269). The third type, the cardiac glands, is found 

 around the cardia, but its area of distribution varies in different 

 animals, and its histological characteristics are not very definite.* 

 There seems to be a general agreement that the chief cells furnish 

 the digestive enzymes of the stomach pepsin and rennin and the 

 cover cells the hydrochloric acid. From a physiological standpoint 

 it is important to remember that the cover 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 impregnated first with pepsin; then, as it is slowly moved 

 into the prepyloric 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 substance which is capable of acting as a chemical excitant 



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

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



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