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The liver
is an organ in vertebrates including humans. It plays a major role in metabolism and has a number of functions in the body including detoxification, glycogen storage and plasma protein synthesis. It also produces bile which is important for digestion. Medical terms related to the liver often start in hepato- or hepatic from the Greek word hepar for "liver".
The adult human liver normally weighs between 1.0 - 2.5 kilograms, and is a soft, reddish-brown "wedge-shaped" organ. It is the largest organ in the abdomen and sits immediately under the diaphragm on the right side of the upper abdomen. The liver lies anterior to the gallbladder and superior to the right kidney.
The liver is supplied by two major blood vessels: the hepatic artery and the portal vein. The hepatic artery normally comes off the celiac trunk. The portal vein brings venous blood from the digestive tract, so that the liver can process the nutrients and toxins extracted from food. The hepatic veins drain directly into the inferior vena cava.
The bile produced in the liver is collected in bile capillaries 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. The cystic duct (from the gallbladder) joins with the common hepatic duct to form the common bile 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.
It is unique as the only human organ capable of natural regeneration of lost tissue.
Physiology
The various functions of the liver are carried out by the liver cells or hepatocytes.
The liver produces and excretes bile required for food digestion. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder.
The liver performs several roles in carbohydrate metabolism:
Gluconeogenesis (the formation of glucose from certain amino acids, lactate or glycerol)
Glycogenolysis (the formation of glucose from glycogen)
Glycogenesis (the formation of glycogen from glucose)
The breakdown of insulin and other hormones
The liver also performs several roles in lipid metabolism:
Cholesterol synthesis
The production of triglycerides (fats).
The liver produces coagulation factors I (fibrinogen), II (prothrombin), V, VII, IX, and XI, as well as protein C, protein S and antithrombin.
The liver neutralizes toxins, most medicinal products, and hemoglobin.
The liver converts ammonia to urea.
The liver stores of a multitude of substances, including glucose in the form of glycogen, vitamin B12, iron, and copper.
In the first trimester fetus, the liver is the main site of red blood cell production. By the 42nd week of gestation, the bone marrow has almost completely taken over that task.
Producing an artifical organ or device capable of emulating most functions of the liver is outside the reach of science in the foreseeable future.
Role in disease
Many diseases of the liver are accompanied by jaundice caused by increased levels of bilirubin in the system. The bilirubin results from the breakup of the hemoglobin of dead red blood cells; normally, the liver removes bilirubin from the blood and excretes it through bile.
Hepatitis, inflammation of the liver, caused mainly by various viruses but also by some poisons, autoimmunity or hereditary conditions.
Cirrhosis is the formation of fibrous tissue in the liver, replacing dead liver cells. The death of the liver cells can for example be caused by alcoholism or other toxins, or hepatitis
Hemochromatosis, a hereditary disease causing the accumulation of iron in the body, eventually leading to liver damage
Cancer of the liver (primary hepatocellular carcinoma or cholangiocarcinoma and metastatic cancers, usually from other parts of the gastrointestinal tract)
Wilson's disease, a hereditary disease which causes the body to retain copper
Primary sclerosing cholangitis, an inflammatory disease of the bile duct, autoimmune in nature.
Primary biliary cirrhosis, autoimmune disease of small bile ducts
Budd-Chiari syndrome, obstruction of the hepatic vein.
A number of liver function tests are available to test the proper function of the liver. These are enzymes that are most abundant in liver tissue, metabolites or products.
Liver transplantation
Liver transplantation is an option for those with irreversible liver failure. Most transplants are done for chronic liver diseases leading to cirrhosis, such as chronic hepatitis C, alcoholism, autoimmune hepatitis, and many others. Less commonly, liver transplantation is done for fulminant hepatic failure, in which liver failure occurs over days to weeks. Liver allografts for transplant usually come from non-living donors who have died from fatal brain injury. Living donor liver transplantation is a technique in which a portion of a living person's liver is removed and used to replace the entire liver of the recipient. This was first performed in 1989 for pediatric liver transplantation. Only 20% of an adult's liver (Couinaud segments 2 and 3) is needed to serve as a liver allograft for an infant or small child. More recently, adult-to-adult liver transplantation has been done using the donor's right hepatic lobe which amounts to 60% of the liver. Due to the ability of the liver to regenerate, both the donor and recipient end up with normal liver function if all goes well. This procedure is more controversial as it entails performing a much larger operation on the donor, and indeed there have been at least two donor deaths out of the first several hundred cases.
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This article is licensed under the GNU Free Documentation License.
It uses material from the Wikipedia article "Liver"
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