V 



CHAPTER XLIV. 

 PHYSIOLOGY OF THE LIVER AND THE SPLEEN. 



The liver plays an important part in the general nutrition of the 

 body. Its functions are manifold, but in the long run they depend 

 upon the properties of the liver cell, which constitutes the anatomical 

 and physiological unit of the organ. These cells are seemingly 

 uniform in structure throughout the whole substance of the liver, but 

 to understand clearly the different functions they fulfill one must 

 have a clear idea of their anatomical relations to one another and 

 to the blood-vessels, the lymphatics, and the bile-ducts. The histol- 

 ogy of the liver lobule, and the relationship of the portal vein, the 

 hepatic artery, and the bile-duct to the lobule, must be obtained from 

 the text-books upon histology and anatomy. It is sufficient here to 

 recall the fact that each lobule is supplied with blood coming in part 

 from the portal vein and in part from the hepatic artery. The blood 

 from the former source contains the soluble products absorbed from 

 the alimentary canal, such as sugar and proteid, and these absorbed 

 products are submitted to the metabolic activity of the liver cells 

 before reaching the general circulation. The hepatic artery brings to 

 the liver cells the arterialized blood sent out to the systemic circu- 

 lation from the left ventricle. In addition, each lobule gives origin 

 to the bile capillaries which arise between the separate cells and which 

 carry off the bile formed within the cells. In accordance with these 

 facts, the physiology of the liver cell falls naturally into two parts, 

 one treating of the formation, composition, and physiological signifi- 

 cance of bile, and the other dealing with the metabolic changes pro- 

 duced in the mixed blood of the portal vein and the hepatic artery 

 as it flows through the lobules. In this latter division the main 

 phenomena to be studied are the formation of urea and the formation 

 and significance of glycogen. 



Bile. From a physiological standpoint, bile is partly an excre- 

 tion carrying off certain waste products, and partly a digestive secre- 

 tion playing an important role in the absorption of fats, and possibly 

 in other ways. Bile is a continuous secretion, but in animals possess- 

 ing a gall-bladder its ejection into the duodenum is intermittent. 

 Bile is easily obtained from living animals by establishing a fistula 

 of the bile-duct or, as seems preferable, of the gall-bladder. The 

 latter operation has been performed a number of times on human 

 beings. In some cases the entire supply of bile has been diverted in 



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