Gallstones form when bile, a liquid made by the liver to digest fats and stored in the gallbladder, hardens into pieces of material that resembles stones. Bile is made up of cholesterol, bile salts, fats, proteins, and bilirubin. Bile salts break up fat. Bilirubin gives bile and stools a yellow color. If bile liquid contains too much cholesterol, bile salts, or bilirubin, it can harden into stones. Bile is made in the liver and stored in the gallbladder until the body needs it to digest fats. When needed, the bile is pushed through a bile duct into the small intestine where it helps break down fats.

There are two primary types of gallstones, cholesterol stones and pigment stones. Cholesterol stones account for 80% of gallstones. They are usually yellow-green and made up mostly of cholesterol. Pigment stones are small, dark stones made up mostly of bilirubin. Gallstones can be as small as a grain of sand or as large as a golf ball. Gallstones can develop as hundreds of small stones or as one large stone or any combination of the two.

Complications arise when gallstones block any of the ducts that allow bile to flow from the liver to the small intestine. Bile trapped in the bile ducts can cause painful inflammation of the gallbladder, the ducts themselves or the liver. The pancreas also secretes other digestive enzymes through the common bile duct. If a gallstone blocks the opening to the pancreatic duct, digestive enzymes can become trapped in the pancreas and cause an extremely painful inflammation known as gallstone pancreatitis.

Identified risk factors for gallstones include obesity, estrogen, ethnicity, gender, age, cholesterol-lowering drugs, diabetes, rapid weight loss, and fasting. Obesity is a major risk factor for gallstones, especially in women. Even being moderately overweight increases the risk of gallstones, most likely because excess weight tends to reduce the amount of bile salts in bile resulting in a high percentage of cholesterol in bile. Excess weight also decreases bile emptying. Excess estrogen from pregnancy, hormone replacement therapy, or birth control pills increase cholesterol levels in bile and reduce bile emptying. Native Americans have the highest rates of gallstones in the US. Mexican Americans also have high rates of gallstones. Women between 20 and 60 years old are twice as likely to develop gallstones. People over age 60 are more likely to develop gallstones. Cholesterol-lowering drugs reduce cholesterol levels in the blood but actually increase levels in bile. People with diabetes usually have very high levels of triglycerides which increase risk of gallstones. Rapid weight loss causes the rapid metabolism of body fat causing the liver to secrete extra cholesterol into the bile. Fasting decreases bile movement which results in increased cholesterol levels in bile.

Gallstone symptoms are called an attack because they occur suddenly. They cause a steady pain in the upper abdomen that increases rapidly and lasts from 30 minutes to several hours, pain in the back between the shoulder blades, pain under the right shoulder and nausea and vomiting.

Laparoscopic surgery is the most common treatment for gallstones. During surgery the cystic duct is cut and the gallbladder removed. For high-risk patients that cannot tolerate surgery, agents that dissolve gallstones can be used. These drugs work slowly, so treatment can last months or years. Gallstones often recur after dissolution therapy.

Reference: http://digestive.niddk.nih.gov/ddiseases/pubs/gallstones/index.htm.

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