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Old Saturday, July 14, 2007
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Sureshlasi Sureshlasi is offline
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Default Topic # 12

liver




liver, largest glandular organ of the body, weighing about 3 lb (1.36 kg). It is reddish brown in color and is divided into four lobes of unequal size and shape. The liver lies on the right side of the abdominal cavity beneath the diaphragm. Blood is carried to the liver via two large vessels: the hepatic artery carries oxygen-rich blood from the aorta, and the portal vein carries blood containing digested food from the small intestine. These blood vessels subdivide in the liver repeatedly, terminating in minute capillaries. Each capillary leads to a lobule. Liver tissue is composed of thousands of lobules, and each lobule is made up of hepatic cells, the basic metabolic cells of the liver. One of the liver's major functions is the manufacture and secretion of bile, which is stored in the gall bladder and released in the small intestine. Bile salts emulsify fats, a process that prepares the latter for digestion by the intestinal enzymes. The hepatic cells assimilate carbohydrates, fats, and proteins. They convert glucose to its stored form, glycogen, which is reconverted into glucose as the body requires it for energy. The ability of the liver to maintain the proper level of glucose in the blood is called its glucose buffer function. The end products of fat digestion, fatty acids, are used to synthesize cholesterol and other substances needed by the body. Excess carbohydrates and protein are also converted into fat by the liver. Digested proteins in the form of amino acids are broken down further in the liver by deamination. Part of the amino acid molecule is converted into glycogen and other compounds. Urea, a waste product of protein breakdown, is produced by the liver, a process which removes poisonous ammonia from the body fluids. The liver is also capable of synthesizing certain amino acids (the so-called nonessential amino acids) from other amino acids in a process called transamination. Some essential components of blood are manufactured by the liver, including about 95% of the plasma proteins and the blood-clotting substances (fibrinogen, prothrombin, and other coagulation factors). The liver also filters harmful substances from the blood. Phagocytic cells in the liver, called Kupffer cells, remove large amounts of debris and bacteria. In addition, the liver stores important vitamins and minerals, including vitamins A, D, K, and B12. Several diseases states can affect the liver, such as hepatitis (an inflammation of the liver) and cirrhosis (a chronic inflammation that progresses ultimately to organ failure). Alcohol alters the metabolism of the liver, which can have overall detrimental effects over long periods of abuse. In 1994, a bioartificial liver, part machine, part cloned living liver cells, was used for the first time. Functioning somewhat like a kidney dialysis machine, the bioartificial liver can support patients with acute liver failure until their own livers regenerate, or it can be used by patients while waiting for a liver transplant.


Flow of blood

The splenic vein, joins the inferior mesenteric vein, which then together join with the superior mesenteric vein to form the portal vein, bringing venous blood from the spleen, pancreas, small intestine, and large intestine, so that the liver can process the nutrients and byproducts of food digestion.

The hepatic veins drain directly into the inferior vena cava.

The hepatic artery is generally a branch from the celiac trunk, although occasionally some or all 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 1/4 is from the hepatic artery.



Flow of bile

The bile produced in the liver is collected in bile canaliculi, 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.



Diseases of the liver

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 viral hepatitis, alcoholism or contact with other liver-toxic chemicals.
  • Haemochromatosis, 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.
  • Gilbert's syndrome, a genetic disorder of bilirubin metabolism, found in about 5% of the population.
  • Glycogen storage disease type II,The build-up of glycogen causes progressive muscle weakness (myopathy) throughout the body and affects various body tissues, particularly in the heart, skeletal muscles, liver and nervous system.
  • There are also many pediatric liver disease, including biliary atresia, alpha-1 antitrypsin deficiency, alagille syndrome, and progressive familial intrahepatic cholestasis, to name but a few.

A number of liver function tests are available to test the proper function of the liver. These test for the presence of enzymes in blood that are normally most abundant in liver tissue, metabolites or products.
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Last edited by Sureshlasi; Saturday, September 01, 2007 at 01:04 AM.
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