Anatomy And Physiology

How the liver functions



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The liver in humans is located in the right side of the abdomen immediately below the diaphragm.  The liver has vital roles in the body that pertain to metabolism as well as other functions such as protein synthesis. The liver has dual blood supply from the hepatic artery which is a branch of the abdominal aorta artery and from the hepatic portal vein coming from the gastrointestinal tract.

The hepatic artery supplies the liver with oxygenated blood and returns blood via the hepatic vein to the vena cava. The portal vein carries blood from the various organs in the digestive system, which is full of nutrients that are absorbed in the intestine into the circulation. This blood also contains other materials that can be toxic such as microbes that succeeded to enter the circulation by passing through the intestinal barrier. These bacteria are then trapped in the liver sinuses where they are acted upon by liver macrohpages that neutralize them. Toxic compounds that were also able to penetrate the intestinal barrier are mostly deactivated in the liver.  An example is the detoxification of the molecule ammonia which is a  product of amino acid metabolism in the liver.  It is detoxified to the molecule urea by enzymatic process, which leads to the excretion of urea in the urine. 

The liver has versatile functions that are related to metabolism as well as other functions.  On the metabolic pathway the liver is important for example in the glucose metabolism which generates energy for the body.  In addition, fatty acids metabolism is also done in the liver and generates energy for the body in the form of ATP molecules. 

The liver is also the site of protein synthesis from amino acids.  In the case of liver failure, the liver' ability to synthesize proteins is impaired.   Especially notable is the protein albumin in which its deficient synthesis leads to hypoalbuminemia.  Albumin is a very important protein that has clinical significance. In normal blood concentration, albumin maintains the colloid osmotic pressure inside the arteries.  Its deficiency leads to low oncotic blood pressure which can lead to escape of fluids to the extracellular space causing edema in the skin, in addition to causing ascites in the peritoneum, which is an accumulation of fluid in the body cavities.

Some of the proteins that its synthesis is impaired in liver failure are part of the clotting factors, which contribute to blood clotting or hemostasis.  Its deficiency can lead to prolonged prothrombin time.  Clinically speaking, the deficiency of these proteins can lead to bleeding disorders.  A person with liver failure can bleed easily due to the deficiency of the clotting factors, which are also proteins.

The liver also has an excretory function in which many compounds that are either synthesized in the liver or are carried by the liver to bile are excreted into the biliary canal such as bilirubin which is a pigment that has clinical significance in the medical condition of jaundice.  In addition, cholesterol and urobilinogen are also secreted by the liver cells to the gallbladder. 

The liver is also the site of detoxifying toxic chemicals such as the base ammonia.  In a condition, which is called hepatic encephalopathy, which is sort of liver failure in which toxic compounds including ammonia are accumulated in the blood to toxic levels.  These compounds then cross the blood-brain barrier and enter the brain tissue causing toxicity to the brain tissue which is called hepatic encephalopathy. 

Another medical condition and which involves the liver and the brain is called Wilson disease.  This disorder is manifested by storage problems of the metal copper in the liver causing its excess in the blood.  This metal can then be carried in the blood to the brain.  Especially vulnerable is the part of the brain which is called the basal ganglia, which its damage can lead to several symptoms such as muscular incoordination.

Liver enlargement occurs in most liver diseases.  In addition, in liver disease usually the liver enzymes concentration in the blood is elevated as occurs for example with alkaline phosphatase which is a marker for the existence of bile stones in the gallbladder.

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