The Principles Of Liver Function Tests Biology Essay

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The liver is located in the upper right section of the abdomen. It is the largest glandular organ in the body. The average weight of the liver for adults is between 1.3-1.5 kg, it contains over 300 billions specialised cells. The liver consists of four lobes of unequal size, it receives two blood supplies, the two different supplies of blood are from the hepatic arteries and the portal vein. 20% of the blood supplied is from the hepatic artery and 80% of the blood supplied is from the portal vein [i] . The main functions of the liver are the storage of glycogen, the production of proteins and bile acids. A special feature of the liver is its ability to regenerate over and over, allowing it to repair itself. . The causes of liver disease are hepatitis, cirrhosis, obstruction, gallstones, liver cancer and a fatty liver. In a recent survey which included 59 nations, the United Kingdom was the 14th highest nation for liver disease, Mexico had the most liver disease cases and Kuwait had the lowest. Twice as many people die from liver disease compared from 1991. (http://www.britishlivertrust.org.uk/home/media-centre/facts-about-liver-disease.aspx)

Now I will discuss in further depth the normal physiology and functions. Apart from the function discussed in previously, the liver also removes toxins from the blood, an exam of this is when the liver converts ammonia to urea which is then released in urine. Ammonia is toxic but urea isn't, allowing urea to be stored for longer periods of time then ammonia. Also it produces bile. The liver also stores glucose in the form of glycogen and then converts glycogen back to glucose when it's required. As well as storing glucose, the liver also stores fat soluble vitamins which are then distributed around the body when they are required through the blood stream. Bile is a digestive fluid which helps break down fats to fatty acids. Bile consists of bilirubin, cholesterol and bile acids. The liver also produces cholesterol which is used in bile. During liver disease, one of the signs of liver disease is the level of bilirubin. Bilirubin is released by the spleen to destroy old red blood cells. Bilirubin is produced by the liver along with many other proteins. The liver plays an important part in drug absorption, when drugs enter the body before they are absorbed by the gut and taken into the blood system; the liver modifies the drugs, according to how much is required by the body, also the liver breaks down some of the drugs that enter the body.

When liver disease occurs it can be either acute or chronic, acute is rapid damage to the liver and chronic is over a period of time, when liver disease occurs liver function tests are carried out in order to the diagnose the patient. These liver tests include the following: Bilirubin levels, this is pigment mainly in bile, it is formed from haemoglobin. This causes bile to have a yellow colour, this is used in the diagnoses of jaundice, and the bilirubin will build up in the body causing the skin and eyes to have a yellow colour. This indicates the liver is not correctly functioning and the extra bilirubin is not being removed from the body. Albumin levels, this is the main protein produced by the liver. Albumin regulates the oncotic pressure in the vascular system; it transports fatty acids in the body which helps regulate the pressure. A low level of albumin is the sign of liver dysfunction. Aspartate aminotransferase is an enzyme produced by the liver; its function is to convert aspartate and ketoglurate to oxaloacetate and glutamate. This test is used to identify whether jaundice is caused by liver disease or a blood disorder. If the levels of AST are low it shows that the jaundice is caused by a liver disease.

Also another liver test is measuring the level of alkaline phosphatase; its function is to remove phosphate groups. ALP is present in the liver, bone and placenta. ALP is released by the liver when the bile ducts a generally blocked; this is sign of liver dysfunction. Apart from the forming of jaundice, hepatitis can also be another symptom of liver disease. Another liver function test is to measure the levels of alanine aminotransferase, this is another enzyme in the liver, this is one of the most specific tests but the levels of ALT don't necessarily correspond to the amount of damage to the liver. When liver damage occurs, ALT is released into the blood stream when a person is suffering from acute liver disease, thus increasing the levels ALT in the blood. The amount of ALT in the blood is normally low, when liver damage occurs other enzymes are released into the blood stream like ALT, this is why it's a more specific indicator for liver damage. One other way of seeing if the liver is damaged is to study clotting of the blood from the patient. When a patient has a damaged liver the blood becomes thinner. Blood normally clots; when a liver is functioning correctly it has a major role in this process.

When checking for liver damage, up to 5 of the tests above are used at once; this then gives more accurate and reliable results. When liver disease occurs and there are more than one possible symptoms like jaundice and hepatitis, using one than tests allows us to understand which of the two is present. One test will not enable a diagnose to be possible, each disease causes different effects and each test will test for those different effects. This also makes the diagnosis easier, ruling out any other possibilities. When looking for liver disease there are a few physicals sign which can be seen:

When cirrhosis of the liver occurs, it becomes more visibly damaged than when other diseases occur, the liver changes shape and begins to break down from the outside as well as from the inside. This is due to the excess alcohol becoming a toxin and breaking down the liver tissue, this liver will no longer function correctly. This liver is now unable to repair itself.

http://audiolivres.org/wp-content/uploads/2009/11/liver-disease1.jpg Last accessed on 6/3/2010

From the current research done on liver disease, the number of liver disease cases has greatly increased; liver disease is the only major cause of death increasing year after year. A liver is considered to have a disease if over 75% of it affected. The UK has a high rate of liver disease compared to other nations; this is mainly due to alcohol consumption. Men have a greater risk to getting liver disease compared with women because men are known to consume more alcohol then women on a regular basis. The liver is a vital organ; it has a wide variety of functions which include storage, modification and production along with other functions which are also need for organs and processes in the body. These methods of analysing liver disease are helpful but don't give clear idea to which disease is causing the liver damage, even when combinations of tests are used. Also the normal values for each level of enzymes, bilirubin and albumin will vary from person to person and the normal values considered also vary from laboratory to laboratory. From the research i have seen and done I am able to conclude that liver disease is going to keep increasing year after year and will only decrease if people change their life styles, liver function tests have increased ability to find a disease within a liver but not always accurately.

Total Words- 1,272

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