Gallstones. Colored X-ray of gallstones (orange) in a patient's gall bladder. Part of the spine (top right to bottom center) and ribs (pale grey) are seen in this frontal view. An endoscope tube runs to lower left. Gallstones are hard deposits of cholesterol or salts that may cause acute pain. The gall bladder stores bile that arrives from the liver via the hepatic duct (dark brown, above and left of endoscope). Bile passes into the digestive tract (black), along with secretions from the pancreatic duct (dark brown, below and right of endoscope). These ducts have been injected with a contrast agent from the endoscope in an ERCP (endoscopic retrograde cholangiopancreatography).