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Hepatic Portal System
Before you can understand the importance of hepatic portal circulation, you need to know how the hepatic portal system works. This system consists of the heart, liver, hepatic portal vein, small intestine, stomach, and large intestine. Most capillaries (tiny blood vessels) empty into veins that carry blood back to the heart. The digestive system, however, has capillaries that empty into capillaries located in the liver.
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Hepatic Portal Circulation and Digestion
The digestive system breaks down foods and delivers nutrients to other parts of the body. Digestion begins in the mouth, where saliva starts to break down solid foods as you chew. Once you swallow your food, it travels through the esophagus. The lower esophageal sphincter, a muscle at the junction of the esophagus and stomach, closes once food has passed. This prevents food from backing up into the esophagus and causing heartburn or gastroesophageal reflux. The stomach stores swallowed food, mixes it with digestive juices, and empties the food into the small intestine.
Liver, pancreas, and intestinal enzymes help to break the food down for easier absorption in the large intestine. Fiber, old intestinal cells, and materials that you can’t digest remain in the colon you eliminate them as feces. During the process of digestion, capillaries in the liver perform several important functions.
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Hepatic Portal Circulation Process
The capillaries in the liver remove some of the substances absorbed in the intestines. They remove glucose for its conversion to glycogen, allow for the conversion of monosaccharides (simple sugars) into glucose, convert amino acids into urea, and remove drugs from the circulatory system for later excretion.
This process allows the liver to serve as a screen for the blood. After the liver carries out is circulatory functions, the concentrations of substances in the blood should be close to normal. The liver also carries out important functions between meals. This organ releases more glucose by performing glycogenolysis (conversion of glycogen to glucose) and converting amino acids to glucose. This allows the body to use glucose properly between meals.
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Liver dysfunction affects this circulatory process, allowing levels of many substances in the blood to increase or decrease outside of normal ranges. When liver dysfunction occurs, the liver secretes high levels of liver enzymes ALT and AST, along with bilirubin, total protein, albumin, and ALP. As levels of bilirubin in the blood increase, the skin takes on a yellow appearance. This condition, known as jaundice, often occurs in newborns with high bilirubin levels.
The hepatic function panel tests helps doctors determine if levels of these substances have increased beyond normal levels. This simple blood tests alerts doctors to the possibility of liver damage caused by alcoholism, hepatitis, and other infections. Early detection of liver damage helps doctors treat liver problems more effectively and prevent more serious complications.