The liver is directly inferior to the diaphragm and is divided into a larger right and smaller left lobe (figure 1), plus two smaller lobes (the caudate and quadrate lobes) which are best viewed from below. Each lobe is further divided into lobules (figure 2), which are the basic functional units of the liver. The liver, and so its lobules, receive blood from the hepatic portal vein and, to a lesser degree, from the hepatic artery. These vessels eventually divide into terminal portal venules and terminal hepatic arterioles which enter the hepatic lobules. Hepatic lobules are approximately hexagonal in shape. At the centre of each lobule is a central vein. At the outer corners of the lobules are portal triads consisting of terminal portal venules, terminal hepatic arterioles and bile ductules (figure 3). Blood from the hepatic arterioles and venules flows through sinusoids between plates of hepatocytes (parenchymal cells). The hepatocytes (figure 4) extract nutrients and toxins from the blood. The sinusoids also contain Kupffer cells which entrap foreign particles and bacteria. The blood, thus filtered, drains into the central veins and is returned to the general circulation through the hepatic vein and inferior vena cava. While blood drains from the outside of the hepatic lobules to the central veins, bile moves in the opposite direction. From the canaliculi between adjacent hepatocytes, the bile moves through ductules to the interlobular bile ducts at the periphery of the lobules, then into larger hepatic ducts which eventually unite to form the left and right hepatic ducts which leave the lobes of the liver. Normally, bile formed in the liver moves from the left and right hepatic ducts into the common hepatic duct and then through the cystic duct to be stored in the gall bladder (also written as one word: gallbaldder).

The gall bladder (figure 5) is a small saccular organ located inferior to the right lobe of the liver. The gall bladder stores bile produced by the liver. When stimulated by the presence of fatty food in the duodenum, the gall bladder contracts. Bile is forced out of the gall bladder, through the cystic duct and into the common bile duct. The common bile duct unites with the pancreatic duct and enters the duodenum through the ampulla of Vater.

The pancreas (figure 6) is located inferior to the stomach. It consists of three portions: a head, body and tail. The pancreas produces secretions, including enzymes, which are important to the digestive process. These secretions drain through the pancreatic duct to enter the duodenum. The head of the pancreas is also drained by a second accessory pancreatic duct. The reason that humans have two pancreatic ducts is that as fetuses we have two separate pancreases (figure 7). Normally, these fuse into one pancreas prior to birth. Besides its digestive secretions, the pancreas produces hormones which are involved in growth and energy metabolism. These hormones are produced in clusters of cells called the islets of Langerhans. The islets of Langerhans contain three principal types of cells: beta cells which produce insulin, alpha cells which produce glucagon and delta cells which produce somatostatin.

English - Japanese Glossary