ANATOMY OF THE LIVER

 

Anatomy

The liver is the largest organ in the abdominal cavity and the most complex. It consists of a myriad of individual microscopic functional units call lobules. The liver performs a variety of functions including the removal of endogenous and exogenous materials from the blood, complex metabolic processes including bile production, carbohydrate homeostasis , lipid metabolism, urea formation, and immune functions. 

The liver arises from the ventral mesogastrium and only the upper posterior surface is outside of that structure. The ligamentum teres and falciform ligament connect the liver to the anterior body wall. The lesser omentum connects it to the stomach and the coronary and triangular ligaments to the diaphragm. The liver is smooth and featureless on the diaphragmatic surface and presents with a series of indentations on the visceral surface where it meets the right kidney, adrenal gland, inferior vena cava, hepatoduodenal ligament and stomach (Figure 4).

Figure . A, Normal gross anatomy of a liver; B, histological slide; B’, histological view.

The liver can be considered in terms of blood supply hepatocytes, Kupffer cells and biliary passages. The liver receives its blood supply from the portal vein and hepatic artery, the former providing about 75% of the total 1500 ml/min flow. Small branches from each vessel—the terminal portal venule and the terminal hepatic arteriole—enter each acinus at the portal triad. Pooled blood then flows through sinusoids between plates and hepatocytes in order to exchange nutrients. The hepatic vein carries efferent blood into the inferior vena cava and a supply of lymphatic vessels drains the liver. 

Parenchymal cells or hepatocytes comprise the bulk of the organ and carry out complex metabolic processes. Hepatocytes are responsible for the liver’s central role in metabolism (Figure 4B'). These cells are responsible for the formation and excretion of bile ; regulation of carbohydrate homeostasis ; lipid synthesis and secretion of plasma lipoproteins; control of cholesterol metabolism; and formation of urea, serum albumin, clotting factors, enzymes, and numerous proteins. The liver also aids in the metabolism and detoxification of drugs and other foreign substances. 

Kupffer cells line the hepatic sinusoids and are part of the reticuloendothelial system, filtering out minute foreign particles, bacteria, and gut-derived toxins. They also play a role in immune processes that involve the liver. 

Biliary passages begin as tiny bile canaliculi formed by hepatocytes. These microvilli -lined structures progress into ductules, interlobular bile ducts, and larger hepatic ducts. Outside the porta hepatis, the main hepatic duct joins the cystic duct from the gallbladder to form the common bile duct, which drains into the duodenum.