SECTION VI 

 THE LIVER AND BILE 



THE liver, the largest gland in the body, is, like the other glands associated 

 with the alimentary tract, formed in the embryo by an outgrowth of the 

 hypoblast lining the alimentary canal. At first it resembles in structure 

 other secreting glands, such as the pancreas, being composed of branch 

 tubules which pour their secretion into a common duct. In the adult, 

 however, the relation of the liver cells to the ducts is entirely subordinated 

 to their relation to the blood-vessels of the liver, and it requires special 

 histological methods to make out the relations between the liver cells and 

 the bile- ducts. The liver, on section, is seen to be divided off into lobules 

 composed of columns of polygonal cells, radiating from the centre like the 

 spokes of a cart-wheel. The portal vein, which drains the blood from the 

 alimentary canal, breaks up into branches which lie at the periphery of the 

 lobules, forming the interlobular veins, and send off numberless capillaries 

 which pass inwards between the columns of cells to join the intralobular vein 

 lying at the centre of the lobule. From the intralobular the blood passes 

 by the large sublobular vein into the hepatic veins and inferior vena cava. 

 In an injected specimen it is easy to see that every liver cell is connected 

 with at least one blood capillary, and the liver thus forms a blood gland, 

 lying as it does at the gate of entrance of blood from the alimentary canal 

 into the general circulation. The portal vein conveys only venous blood to 

 the liver. In order to supply oxygen to the working liver cells, this organ 

 receives a second supply of arterial blood by the hepatic artery derived from 

 the cceliac branch of the aorta. The branch of the hepatic artery runs with 

 the branches of the portal vein in the connective tissue of Glisson's capsule 

 surrounding the lobules, and breaks up into capillaries which are in free 

 communication with the capillaries derived from the portal system and pour 

 their blood finally into the hepatic vein. 



As might be expected from its structure, the secretory functions of the 

 liver represent but a small proportion of its activities in the body. The liver 

 is, in fact, the greatest chemical factory of the body, receiving by the portal 

 vein the products of digestion as they are absorbed from the alimentary 

 canal. It converts these into other substances, breaking them down or 

 building them up according to the needs of the body as a whole. Thus, when 

 carbohydrates are being absorbed in quantity it converts the glucose 

 contained in the portal blood into glycogen which it stores up, reconverting 



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