Gastroenterology is the study of the gastrointestinal (GI) tract of the body. A gastroenterologist diagnoses and treats diseases of the digestive organs, including the stomach, esophagus, intestines, pancreas, liver and gallbladder. This specialist treats conditions such as abdominal pain, nausea and vomiting, ulcers, diarrhea, cancer in the GI tract, and jaundice. A gastroenterologist also performs complex diagnostic procedures, including the use of endoscopes to see and treat internal organs.