In what part of the body do gallstones form?

Gallstones form in the gallbladder, which is a small pouch located beneath the liver that stores bile—a digestive fluid produced by the liver. Bile helps in the digestion of fats, and when there is an imbalance in the substances that make up bile, solid particles can form. These particles can gradually develop into stones of varying sizes. Factors contributing to gallstone formation include high levels of cholesterol in bile, imbalances in bile salts, and the presence of bilirubin, among others. The gallbladder contracts to release bile into the intestines during digestion; however, if bile contains too much cholesterol or bilirubin, it can harden into stones.

The other options point to organs involved in related but different functions. For instance, while the liver produces bile, it does not store it or produce gallstones. Similarly, the kidneys are involved in filtering blood and producing urine, and the pancreas has a role in digestion and hormone regulation but does not relate to gallstone formation. Therefore, the correct answer, the gallbladder, is specifically where gallstones develop, making it the appropriate choice.