CHAPTER XL 

 ABSORPTION. 



Absorption is a process by which nutritive material from the tissue 

 spaces, from the serous cavities, from the interior of the lungs and from the 

 mucous surfaces of the body, and waste materials from the tissues are trans- 

 ferred into the blood. 



The absorption of nutritive materials from the tissue spaces and from the 

 serous cavities may be regarded as an act of resorption or a return to the 

 blood of nutritive material which has passed through the walls of the capil- 

 lary blood-vessels in excess of that needed for purposes of nutrition, and 

 which if not returned would lead to an accumulation and the development of 

 edematous conditions; the absorption of oxygen from the lungs is essential 

 to the maintenance of nutritive activity, to the oxidation of foods and the 

 liberation of the energy; the absorption of new nutritive materials from the 

 mucous surfaces of the entire alimentary canal, but more especially from 

 that of the small intestine, materials that have been produced out of the 

 foods by the digestive process, is essential to the maintenance of the 

 quantity and quality of the blood. 



The absorption of the products of metabolism, of carbon dioxid, urea and 

 other nitrogen -holding compounds from the tissues into the blood is essential 

 to the continuance of their activities as well as a necessary preliminary to 

 their elimination from the body. 



The anatomic mechanisms involved in the absorptive process are, pri- 

 marily, the tissue or lymph-spaces, the lymph- and blood-capillaries; second- 

 arily, the lymph-vessels and the veins. 



Tissue or Lymph-spaces ; Lymph-capillaries. Everywhere through- 

 out the body, in the connective-tissue system and in the interstices of the 

 several structures of which an organ is composed, are found spaces or clefts 

 of irregular shape and size, determined largely by the structure of the organ 

 in which they are found, which have been termed tissue or lymph-spaces, 

 from the fact that they contain a clear fluid, the lymph. These spaces are 

 devoid for the most part of any endothelial lining, but as they communicate 

 more or less freely one with another, there is a circulation of lymph through 

 them and around the islets of tissue (Fig. 86) . In addition to the connective- 

 tissue lymph-spaces, different observers have described special spaces or 

 clefts in organs such as the kidney, liver, spleen, testicle, and in all secreting 

 glands between their basement membrane and the surrounding blood- 

 vessels, all of which contain a greater or less quantity of lymph. Within the 

 brain, spinal cord, bone, and other tissues it has been shown that the smallest 

 blood-vessels and capillaries are bounded and limited by a cylindrical sheath 

 containing lymph, which is known as a perivascular lymph-space. A 

 similar sheath surrounds the smallest nerve-bundles and fibers, enclosing a 

 perineural lymph-space. The large serous cavities of the body, pleural, 



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