Anatomy of the Liver Synthesis, Storage and Regulation of Biological Compounds Purification, Transformation and Clearance Liver Function Tests Measures of Liver Damage Anatomy of the Liver Aside from the skin, the liver is the largest organ in the body. It is located below the diaphragm in the upper quadrant of the abdominal cavity. The weight of an adult’s liver weighs about three pounds. The liver is separated into right and left lobes by the ligaments; the right lobe is much larger than the left lobe. The cells of the liver are referred as hepatocytes. Synthesis, Storage and Regulation of Essential Biological Compounds Most proteins are synthesized and secreted by the liver. One of the most abundant serum proteins is albumin. Abnormal liver function can results in decreased production of albumin, which may lead to a serious condition called edema, which is the swelling of tissues due to fluid accumulation. The liver also synthesizes blood clotting factors, which prevent excessive bleeding. Hepatocytes produce bile, a greenish fluid that is important for digestion and absorption of dietary fats. Bile is temporarily stored in the gallbladder before it is secreted into the small intestine. Obstruction of bile ducts in the liver can lead to malabsorption of dietary fats, foul-smelling diarrhea caused by fats that were not absorbed, and jaundice, yellowing of eyes and skin. The alkaline phosphatase and the GGT are elevated in a large number of disorders that affect the drainage of bile, such as a gallstone or tumor blocking the common bile duct, or alcoholic liver disease or drug-induced hepatitis, blocking the flow of bile in smaller bile channels within the liver. Liver also manufactures lipids and their derivatives. Cholesterol is found in cell membranes and helps maintain the physical integrity of cells. Lipoproteins transports cholesterol and energy source in the form of fatty acids between the liver and body tissues via the circulatory system. The body utilizes glucose as its main energy source. The liver is designed to storage glucose, in the form of glycogen, and releases the substance to tissues as needed. Deposition and release of fat-soluble vitamins also occur in the liver. By maintaining the appropriate levels of substances in the blood, liver plays an essential role in body homeostasis. Purification, Transformation and Clearance The liver removes harmful substances from blood and transforms them into less harmful compounds via the use of liver enzymes (metobolize). Ammonia is a byproduct of protein digestion; it is toxic in elevated levels, especially to the brain. The liver converts ammonia to urea, a less toxic compound, which is excreted into the urine by the kidneys. The process of old red blood cell destruction in the spleen results in formation of bilirubin, a yellow pigment substance that binds to albumin. The liver absorbs bilirubin and modifies it so it can be excreted into bile. Jaundice is caused by overproduction or under clearance of bilirubin. The liver generally detoxifies toxic chemical agents and poisons. Exposure to chemicals and toxins, especially in a long-term, leads to ineffectiveness of detoxification processes and liver failure. The liver metabolizes (uses enzymes to break down) and inactivates most hormones and ingested drugs. Individuals with significant liver damage can experience hormonal imbalance, with possible symptoms of masculinization or feminization. In addition, nearly all drugs are modified or degraded in the liver before they enter the systemic circulation. Over consumption of alcohol, which is primarily metabolized in the liver, can lead to damage or destruction of hepatocytes. Liver Function Tests The term "liver function tests" and its abbreviated form "LFTs" is a commonly used term that is applied to a variety of blood tests that assess the general state of the liver and biliary system. Routine blood tests can be divided into those tests that are true LFTs, such as serum albumin or prothrombin time, and those tests that are simply markers of liver or biliary tract disease, such as the various liver enzymes. Measures of Liver Damage The ALT and AST are enzymes that are located in liver cells and leak out and make their way into the general circulation when liver cells are injured. The ALT is thought to be a more specific indicator of liver inflammation, since the AST may be elevated in diseases of other organs such as the heart or muscle. In acute liver injury, such as acute viral hepatitis, the ALT and AST may be elevated to the high 100s or over 1,000 IU/L. In chronic hepatitis or cirrhosis, the elevation of these enzymes may be minimal (less than 2-3 times normal) or moderate (100-300 IU/L). Mild or moderate elevations of ALT or AST are nonspecific and may be caused by a wide range of liver diseases. ALT and AST are often used to monitor the course of chronic hepatitis and the response to treatments, such as prednisone and interferon. Pediatric Viral Hepatitis Network. COPYRIGHT © 2003, New York University School of Medicine. All rights reserved.