Page:Structure and functions of the body; a hand-book of anatomy and physiology for nurses and others desiring a practical knowledge of the subject (IA structurefunctio00fiskrich).pdf/156

 into lobules, in the center of each of which is a blood-vessel, the intralobular vein, from which a network of capillaries extends to the edge of the lobule, there being a capillary on either side of each row of cells. Between the cells also are the intercellular biliary passages, roots of the bile ducts which exist in the connective tissue between the lobules and which join to form two main ducts, one from the right and the other from the left lobe. By the union of these two ducts the hepatic duct is formed, which, after a course of one or two inches, joins the cystic duct from the gall-bladder to form the ductus communis or common bile duct.

The liver has a double blood supply, the hepatic artery from the celiac axis bringing nourishment to the connective tissue and the walls of the blood-vessels, while the capillaries between the cells come from the portal vein, which, being formed by the junction of the superior and inferior mesenteric, the splenic and the gastric veins, contains the proteins and carbohydrates absorbed during digestion. After its passage through the liver this blood from the portal vein is collected once more into the hepatic veins, which convey it to the inferior vena cava. During its passage, however, various changes take place, for the liver plays an important part in the metabolic processes of the body.

The liver has two principal functions, the secreting of bile and the storing up of glycogen. The secretion of bile, which is a very important aid to digestion, is probably a reflex act, the presence of peptones in the portal blood after meals acting as a stimulant to the liver cells. For food at once increases the secretion of bile, which is poured from the cells into the small bile ducts and finally passes into the hepatic duct and so to the gall-bladder, where it is stored until needed. Although the flow from the liver is constant, the amount secreted reaches its maximum when the food gets down into the small intestine, that is, four or five hours after eating, there being a lull before that. Apart from the process of secretion,