PHYSIOLOGY OF ABSORPTION. 



STRUCTURE OF THE ORGANS OF ABSORPTION. 



The mucous membrane of the entire intestinal tract, so far as it is 

 lined by a single layer of cylindrical epithelium, that is, from the cardiac 

 orifice to the anus, is capable of absorption. The buccal cavity and the 

 esophagus can take part in this process only to an exceedingly limited 

 extent, on account of their thick, many-layered squamous epithelium. 

 Nevertheless, poisoning, as, for example, with potassium cyanid, may 

 take place by absorption from the mouth alone. The capillary blood- 

 vessels, as well as the chyle- vessels, of the mucous membrane act as the 

 absorbing channels of the intestinal tract. The former convey the 

 materials absorbed almost wholly through the portal vein to the liver, 

 while the latter, uniting in their further course with lymph- vessels, dis- 

 charge the absorbed chyle or milky juice through the thoracic duct into 

 the blood at the junction of the subclavian and internal jugular veins. 



From the stomach are absorbed aqueous salt-solutions (within six 

 minutes), sugar (namely, grape-sugar, milk-sugar, cane-sugar and mal- 

 tose) in aqueous solution in moderate amount, in alcoholic solution in 

 somewhat larger amount; dextrin and peptone, chiefly in concentrated 

 solutions, in lesser amount; and poisons, especially when dissolved in 

 alcohol. Klemperer and Scheurlen observed that, in the dog, neither 

 fat nor the fatty acids were absorbed. The empty stomach absorbs 

 more rapidly than that filled with food. Diseases of the stomach and 

 fever cause delayed absorption. 



In addition to absorption, an active secretion of water into the stomach, 

 takes place, in general, in greater degree in proportion as the amount of absorbed 

 substances is greater. 



The small intestine constitutes the principal field of absorption, pre- 

 senting, especially in its upper half, through its many folds of mucous 

 membrane and through the innumerable cone-shaped villi projecting from 

 them, an extraordinary expanse of surface for absorption. The villi are 

 close together at their bases, so that the entire surface of the mucous 

 membrane appears to be covered with them. In the spaces between 

 their bases the numerous simple tubules of Lieberkiihn's glands empty. 

 Each villus is to be regarded as a projection of the entire mucous mem- 

 brane, for it contains all of the elements comprised within it. 



The cloak-like covering of the villi consists of a single layer of cylin- 

 drical epithelium with intervening isolated mucous goblet-cells. The 

 surface of the cells directed toward the lumen of the intestine is poly- 

 gonal (Fig. 127, D) and, viewed from the side (C), exhibits a broad 

 seam-like outline, which was formerly considered the thickened wall of 

 the cell-membrane and was designated by the term "lid-membrane." 

 This seam exhibits a delicate longitudinal striation, which was inter- 

 preted in part as the expression of the constitution of the lid, of rods 



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