PART V 



DIGESTION 



CHAPTER XLVIII 

 GENERAL PHYSIOLOGY OF THE DIGESTIVE GLANDS 



The function of digestion is to bring the food into such a condition 

 that it can be absorbed through the intestinal epithelium into the blood 

 and lymph. Carbohydrates are broken down as far as monosaccharides ; 

 neutral fats are split into fatty acids and glycerine; and proteins are 

 broken down into the amino acids. The agencies which effect these 

 decompositions are the digestive enzymes, or ferments, contained in the 

 various digestive fluids or juices. The digestive juices are produced by 

 glands, which are most numerous in the upper levels of the gastro- 

 intestinal tract, the lower levels having as their main function that of 

 absorption of the digested products. In order that the masses of food 

 may be kept in a state of proper consistency, and that they may move 

 readily along the digestive canal, numerous mucous glands are also 

 scattered along the whole extent of the canal. Some of the digestive 

 glands, such as the main salivary glands, the pancreas, and the liver, 

 discharge their secretions into the digestive canal by special ducts, 

 whereas others, such as the isolated salivary gland follicles in the mouth, 

 the gastric glands and the crypts of Lieberkuhn in the intestine, do not 

 have an anatomically distinct duct, but discharge their secretions directly 

 into the digestive tube. 



It will be convenienl to consider, first of all, certain properties that are 

 common to the digestive glands, and then, the conditions under which 

 each gland functionates during digestion. 



MICROSCOPIC CHANGES DURING ACTIVITY 



Structurally the active part of the glands, represented by the acinus 

 or tubule, is composed of a basement membrane lined internally with the 

 secreting epithelium. Outside the basal membrane are the lymph spaces 

 and blood capillaries. Alter the gland has been ;i1 rest, the cells become 



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