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What are gallstones? |
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Gallstones are stones that form in the gall (bile). Bile is a watery liquid made by the cells of the liver that is important for digesting food in the intestine, particularly fat. Liver cells secrete the bile they make into small canals within the liver. The bile flows through the canals and into larger collecting ducts within the liver (the intrahepatic bile ducts). The bile then flows within the intrahepatic bile ducts out of the liver and into the extrahepatic bile ducts-first into the hepatic bile ducts, then into the common hepatic duct, and finally into the common bile duct. From the common bile duct, there are two different directions that bile can flow. The first direction is on down the common bile duct and into the intestine where the bile mixes with food and promotes digestion of food. The second direction is into the cystic duct, and from there into the gallbladder (often misspelled as gall bladder). Once in the gallbladder, bile is concentrated by the removal (absorption) of water. During a meal, the muscle that makes up the wall of the gallbladder contracts and squeezes the concentrated bile in the gallbladder back through the cystic duct into the common duct and then into the intestine. (Concentrated bile is much more effective for digestion than the un-concentrated bile that goes from the liver straight into the intestine.) The timing of gallbladder contraction-during a meal-allows the concentrated bile from the gallbladder to mix with food.
Gallstones usually form in the gallbladder; however, they also may form anywhere there is bile--in the intrahepatic, hepatic, common bile, and cystic ducts. Gallstones also may move about within bile, for example, from the gallbladder into the cystic or common duct.
What causes gallstones?
Gallstones are common--they occur in approximately 20% of women in the US, Canada and Europe--but there is a large variation in prevalence among ethnic groups. For example, gallstones occur 1 ½ to 2 times more commonly among Scandinavians and Mexican-Americans. Among American Indians, gallstone prevalence reaches more than 80%. These differences probably are accounted for by genetic (hereditary) factors. First-degree relatives (parents, siblings, and children) of individuals with gallstones are 1 ½ times more likely to have gallstones than if they did not have a first-degree relative with gallstones. Further support that genetic factors are important in determining who gets gallstones comes from twin studies. Among non-identical pairs of twins (who share 50% of their genes with each other), both individuals in a pair have gallstones 8% of the time. Among identical pairs of twins (who share 100% of their genes with each other), both individuals in a pair have gallstones 23% of the time. There are several types of gallstones and each type has a different cause. Cholesterol gallstones are made primarily of cholesterol. They are the most common type of gallstone, comprising 80% of gallstones in individuals from Europe and the Americas. Cholesterol is one of the substances that liver cells secrete into bile. (Secretion of cholesterol into bile is an important way in which the liver eliminates excess cholesterol from the body.) In order for bile to carry cholesterol, the cholesterol must be dissolved in the bile. Cholesterol is a fat, however, and bile is an aqueous or watery solution; fats do not dissolve in watery solutions. In order to make the cholesterol dissolve in bile, the liver also secretes two detergents-bile acids and lecithin-into the bile. These detergents, just like dish-washing detergents, dissolve the fatty cholesterol so that it can be carried by bile through the ducts. If the liver secretes too much cholesterol for the amount of bile acids and lecithin it secretes, some of the cholesterol does not dissolve. |
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Bigdaddy |
2 Weeks, 1 day, 10 hours, 34 minutes ago |
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