They treat and diagnose conditions and issues that can impact or concern the gastrointestinal tract and liver. They assess the structure of the patient's digestive tract and are experts in digestive tract diseases, including polyps, peptic ulcer disease, or pancreatitis. A gastroenterologist is a specialist in gastrointestinal diseases. Gastroenterologists treat all the organs in your digestive system, including your GI tract (esophagus, stomach and intestines) and biliary organs (your liver, bile ducts, pancreas and gallbladder.)