Physiology of Absorption, 



189. The Organs of Absorption. 



THE mucous membrane of the whole intestinal tract, as far as it is 

 covered by a single layer of columnar epithelium i.e., from the 

 cardiac orifice of the stomach to the anus is adapted for absorption. 

 The mouth and oesophagus, lined as they are by stratified squamous 

 epithelium, are much less adapted for this purpose. Still, poisoning is 

 caused by placing potassium cyanide in the mouth. 



The channels of absorption in the intestinal tract are (1) the 

 capillary Hood-vessels; and (2) the lacteals of the mucous membrane. 

 Almost the whole of the substances absorbed by the former pass into 

 the rootlets of the portal vein, and traverse the liver, while those 

 that enter the lacteals really pass into lymphatics, so that the chyle 

 passes through the thoracic duct, and is poured by it into the blood, 

 where the thoracic duct joins the subclavian vein. 



Watery solutions of salts e.g., potassium iodide (in ^-li hours), 

 grape-sugar, poisons, peptones, and in a still higher degree, alcoholic 

 solutions of poisons are absorbed from the stomach. 



The greatest area of absorption is undoubtedly the small intestine, 

 especially its upper half (Landois and L6pine). 



190. Structure of the Small and Large Intestines. 



[The wall of the small intestine consists of four coats ; which from 

 without inwards are named serous, muscular, sub-mucous, and mucous. 



The serous coat has the same structure as the peritoneum i.e., a thin basis of 

 fibrous tissue covered on its outer surface by endothelium. 



The muscular COat consists of a thin outer longitudinal and an inner thicker 

 circular layer of non-striped muscular fibres. 



The sub-niUCOUS coat consists of loose connective-tissue containing large blood- 

 vessels and nerves, and it connects the muscular with the mucous coat.] 



The mucOUS coat is the most internal coat, and its absorbing surface is largely 

 increased by the presence of the valvulse conniventes and villi. [The valvulce 

 conniventes are permanent folds of the mucous membrane of the small intes- 

 tine, arranged across the long axis of the gut. They pass round a half 

 or more of the inner surface of the gut. They begin a little below the 



