THE FUNCTION OF THE V1LLI 287 



Structure of the Villi. The mucous membrane of 

 the small intestine is covered by tiny conical processes 

 which extend from the end of the pylorus of the stomach 

 to the end of the ileum. These, when examined under 

 the microscope, show a conical process covered with 

 columnar epithelial cells, each cell containing a nucleus, 

 and here and there goblet cells which secrete mucus. 

 The epithelial cells rest upon a basement membrane. 

 In the body of the villus that portion within the 

 mucous membrane contains a net-work of connective 

 tissue supporting arterioles, capillaries, venules, and 

 lymphatic vessels. In the centre of the villus is a 

 lymph capillary, usually single, with epithelial cells in 

 its wall. 



The Function of the Villi. The action of the cells 

 of the villi during digestion is to absorb the nutritive 

 products of digestion. These products are taken 

 from the intestinal canal and transferred into the 

 lymph spaces within the body of the villi, from which 

 they are finally taken up by the blood capillaries and 

 lymphatics. There are two routes by which the nutri- 

 tive material passes into the general blood stream. 

 The capillaries which enter the villi and are in inti- 

 mate relation with the lymph space give up their 

 nutritive materials (blood plasma) by a transudation 

 through their walls, which forms the lymph; mean- 

 time the nutritive material absorbed from the intes- 

 tines by the cells of the villi undergoes metabolic 

 changes and enters the arterial capillaries from the 

 lymph spaces. This fenourished blood in the arterial 

 capillaries passes into the venules and then into the 

 larger veins of the intestines, to be conveyed to the 

 liver, which uses it to maintain its functions. The 

 lymph contained in the lymph spaces within the villi 

 is called chyle (a milk-white fluid), which is absorbed 

 by the lymphatic vessels called lacteals, and these 

 empty into the large mesenteric lymphatics to drain 



