Cholelithasis, more commonly known as gallstones, are hardened deposits of bile in the gallbladder. Approximately 10 to 15% of Americans experience gallstones in their lifetime. To understand gallstones and why they develop, one needs to understand the gallbladder and how it functions Gallbladder The gallbladder is a small, hollow organ located beneath the liver that stores bile in high concentrations. Bile is a bitter alkaline fluid produced by the liver to support digestion. The liver sends bile into the gallbladder by means of the common hepatic duct. When food containing fat enters the digestive tract, the intestines release cholecystokinin. The cholecystokinin causes the gallbladder to contract and release the bile from the gallbladder into the small intestines through the common bile duct to digest fats. Bile is made up of water and bile salts or acids. These acids include—taurocholic acid and glycocholic acid (derivatives of cholic acid) and taurochenodeoxycholic acid and glycochenodeoxycholic acid (derivatives of chenodeoxycholic acid). Gallstones can be divided into two categories: cholesterol or pigment. Cholesterol gallstones Most gallstones, about 75%, are made up of cholesterol. Cholesterol gallstones result from biliary supersaturation caused by: An increased secretion of cholesterol into the gallbladder Gallbladder hypomotility—a case in which crystals remain in the gallbladder so long they become stones Accelerated cholesterol nucleation and crystallization Mucin (a glycoprotein component of mucus) gel accumulation Pigment gallstones Pigment gallstones can be black or brown depending on what they are made of.

Risk factors There are several risk factors of gallstones: Age Sex Ethnicity Rapid weight loss Chronic hemolytic disorders Obesity and diabetes mellitus Certain medications Age The risk for gallstone development increases significantly after the age of 40. Individuals between 40 and 69 are 4 times more likely to develop gallstones than younger people. Sex Women of reproductive age are also at greater risk of developing gallstones. They are 4 times more likely to develop gallstones than men. However, the sex specific difference in risk decreases after menopause. The risk is thought to be higher in women of reproductive age because of hormone composition, pregnancy and the use of oral contraceptives. Estrogen reduces the production of bile salts and increase secretion of cholesterol in the gallbladder resulting in cholesterol supersaturation. Progesterone synergistically promotes stone formation by causing hypomobility in the gallbladder. Ethnicity Mexican Americans and Native Americans are at a higher risk for gallstones than other ethnic groups. Rapid weight loss Rapid weight loss promotes gallbladder formation when weight loss is due to a decrease in caloric intake. This promotes bile stasis. In addition, lipolysis, the breakdown of fats and other lipids, enhances cholesterol motility and secretion in the gallbladder. Together, these conditions creates an environment that promotes bile supersaturation with cholesterol and subsequently gallstone development.