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 anatom- 

 ical and physiological unit of the organ, although there is histo- 

 logical evidence that some of the endothelial cells of the capillaries 

 of the liver have marked phagocytic properties, and it is possible 

 that their activity may play a contributory part in some of the 

 functions of the liver, for example, in the destruction of the red 

 corpuscles that precedes the formation of bile pigments. The liver 

 cells are seemingly uniform in structure throughout the whole sub- 

 stance of the liver, but to understand clearly the different functions 

 they fulfil 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 histology 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 materials absorbed from the alimentary canal, such as sugar 

 and the split products (amino-acids) of protein, 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 cir- 

 culation 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 physio- 

 logical significance of bile, and the other dealing with the metabolic 

 changes produced in the mixed blood of the portal vein and the 

 hepatic artery as it flows through the lobules. In this latter divi- 

 sion the main phenomena to be studied are the formation of urea 

 and the formation and significance of glycogen, but it cannot be 

 doubted that the liver possesses other important metabolic func- 

 tions which at present are imperfectly understood, such, for 

 example, as its relations to the production of fibrinogen and of 

 antithrombin, which have been referred to in the section on Blood. 



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

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



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