CHAPTER XI 

 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 across 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 their 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 blood- and lymph-capillaries; second- 

 arily, the blood-vessels (veins,) and the lymph-vessels. 



Tissue or Lymph-spaces. Everywhere throughout 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. 84). 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, 

 peritoneal, pericardial, etc., are also to be regarded as lymph-spaces. The 



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