Introduction to the Functions of the Liver
The liver is a vital organ that performs a variety of important functions. It is unique among the internal organs for its ability to regenerate following tissue loss. Glucose homeostasis is maintained by the liver by way of glucose storage (as glycogen), glycogenolysis, and gluconeogenesis. In addition to glycogen, the liver is an important site for iron, copper, triglyceride, and lipid-soluble vitamin storage. A large number of serum proteins, such as albumin, clotting factors, and complement, are synthesized in the liver. Proper liver function is crucial for the catabolism of serum proteins and hormones and for the detoxification of exogenous substances, including many drugs. The liver is also the source of bile production, which is important for fat absorption within the small bowel.
Normal Anatomy and Histology of the Liver
The liver is located in the right upper quadrant of the abdomen, immediately beneath the diaphragm. Two hepatic lobes are recognized: a larger right lobe and a smaller left lobe. The hepatic artery and portal vein provide the liver with a dual blood supply. The hepatic artery originates from the celiac axis and is the liver’s source of more highly oxygenated blood. The portal vein is formed primarily by the convergence of the splenic vein and superior mesenteric vein. Because of its unique circulation, the portal vein provides the liver with metabolic substrates from the gut and provides a mechanism for ingested substances to be processed before entering the systemic circulation. The hepatic veins empty into the inferior vena cava and carry blood away from the liver and into the systemic circulation. The bile carrying ducts of the liver are called hepatic ducts. The right and left hepatic ducts empty into a common hepatic duct that merges with the cystic duct of the gallbladder to form the common bile duct (Figure 11-1).
Anatomy of the liver. (A) Anterior and (B) posteroinferior view. Source: Reproduced, with permission, from McKinley M, O’Loughlin VD. Human Anatomy. 2nd ed. New York, NY: McGraw-Hill; 2008.
From a microanatomical perspective, the liver is composed of structural units called hepatic lobules. It is easiest to think of the hepatic lobule as a two-dimensional hexagon arranged around a terminal hepatic venule (a.k.a., central vein). Portal tracts (a.k.a., portal triads) are located at the peripheral angles of the hexagon. Portal tracts contain branches of hepatic artery, portal vein, and hepatic duct and are supported by stroma. Surrounding the portal tract is a layer of hepatocytes called the limiting plate. The majority of the hepatic lobule is made up of plates of hepatocytes measuring 1–2 cells thick that radiate from the terminal hepatic venule to the periphery of the lobule. These hepatic plates are surrounded by hepatic sinusoids (Figures 11-2 and 11-3)...