What Are the Functions of the Liver in Digestion?
The liver is a large, triangular organ in the upper right quadrant of the abdomen, on top of the stomach. It is the largest organ inside the body and, in a healthy adult, weighs approximately three pounds and extends almost the width of the abdomen. The liver has two lobes that are separated by a ligament. The right lobe is much larger. The liver is a multi-system organ. It has more than 500 functions within the body.
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Primary Functions
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The liver is often associated with filtration, and its primary function is to process and remove toxins from the blood. Most of the drugs we take are processed by the liver and several medications, like acetaminophen, can cause severe liver damage if overdosed upon. But, in addition to filtration, the liver has other functions that affect all systems of the body. As part of the immune system it produces immune factors and removes bacteria from the blood stream. It also stores glycogen as an emergency energy source and iron for red blood cell production. As a digestive organ, the liver serves two purposes--filtration and bile production.
Digestive Function - Filtration
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Not everything we ingest is beneficial to the body. A lot of the stuff we eat may have bacteria (or other pathogens), there may be chemicals that are dangerous to the body or there may simply be an excess of beneficial nutrients (like glucose and amino acids). The liver removes as many of the toxins and unusable materials as it can before allowing the blood to reach the rest of the cells in the body. It also takes some elements from the blood for use in other processes. Dietary iron is taken to form blood cells, some sugars are converted to glucose for use in the cells and some of that glucose is converted to glycogen and stored in the liver. Excess amino acids are processed into urea. The liver also stores some A and B vitamins.
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Digestive Function--Bile and Urea Production
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When the liver filters out toxins, it secretes those toxins into two major substances: urea and bile. Urea is a byproduct of amino acids and is a major component in urine. Bile is made up of cholesterol and waste products and acts both as a digestive and an excretory agent in the intestines. The liver produces bile constantly. It is stored in a pouch called the gall bladder. As a digestive agent, bile breaks down fats into their smallest parts, for easy absorption. As an excretory agent, it deposits toxins, filtered by the liver, into to the intestines for removal during defecation.
The Liver's Digestive Sequence
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The liver's function in the digestive system is a continuous loop. The liver produces bile, which is released into the gall bladder. When we eat fatty foods, the gall bladder releases bile into the intestine to break down fats and remove wastes. The broken down nutrients are then absorbed by the capillaries in the intestines, into the blood stream. That blood collects in the hepatic portal vein and travels back to the liver. The liver processes nutrients and filters toxins then releases the blood into the main arterial system to feed the rest of the body. The filtered toxins and excess blood by-products are turned into urea and bile. The urea goes to the kidneys where it's excreted in urine. The bile goes to the gall bladder where it is secreted into the intestines and the digestive process starts all over again.
Unique Qualities
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One thing that makes the liver unique, among all the organs in the body, is that the liver can actually regenerate. If a portion of the liver is removed that portion will actually grow back. The liver is also one of the few organs that can be donated by a live donor. A portion of the donor's healthy liver can be cut out and the donor's liver will regenerate. This regenerative ability is due, in large part, to the fact that the liver is constantly exposed to toxins and other damaging agents. However, repeated severe damage ( as with alcoholism, disease and drug use), will hinder regeneration and cause the liver to fail.
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