Liver

Monday, December 22, 2008

Located in the upper abdomen, the liver is the largest organ and one of the most vital one as it does important jobs such as protein synthesis, glycogen storage, and removing waste products and worn out cells from the blood. The liver is necessary for survival, and a human can only last up to 24 hours without liver function. It also produces bile, an alkaline compound which aids in digestion by breaking down fat. It weighs about 3.5 pounds, measures about 8 inches horizontally and 6.5 inches vertically, and is 4.5 inches thick. It is a soft, pinkish-brown, triangular organ. The liver is the only internal human organ capable of natural regeneration of lost tissue. So, as little as 25% of a liver can regenerate into a whole liver. Medical terms related to the liver often start in hepato- or hepatic from the Greek word for liver.

Gross anatomy divides the liver into four lobes based on surface features. The falciform ligament is visible on the front of the liver. This divides the liver into a left anatomical lobe, and a right anatomical lobe. If the liver flipped over, to look at it from behind (the visceral surface), there are two additional lobes between the right and left. These are the caudate lobe (the more superior), and below this the quadrate lobe.

The bile secreted by the liver is collected in the bile canaliculi (tiny canals), which merge to form bile ducts. These eventually drain into the right and left hepatic ducts, which in turn merge to form the common hepatic duct. Bile can either drain directly into the duodenum via the common bile duct or be temporarily stored in the gallbladder via the cystic duct. The common bile duct and the pancreatic duct enter the duodenum together at the ampulla of Vater. The branchings of the bile ducts resemble those of a tree, and indeed the term "biliary tree" is commonly used in this setting.

The splenic vein joins the inferior mesenteric vein, which then together join the superior mesenteric vein to form the hepatic portal vein, bringing venous blood from the spleen, pancreas, stomach, small intestine, and large intestine, so that the liver can process the nutrients and by-products of food digestion. The hepatic veins of the blood can be from other branches such as the superior mesenteric artery. Approximately 60% to 80% of the blood flow to the liver is from the portal venous system, and one fifth of the blood flow is from the hepatic artery.