Gastroenterology is defined as the diagnosis and treatment of diseases affecting the entire digestive system including the esophagus, the stomach, the small and large intestines, the liver, pancreas and the gallbladder. Gastroenterologists use a number of techniques to view the organs of the digestive tract. The most common tests that they perform are colonoscopy and upper GI- endoscopy. Colonoscopy is performed to examine the large intestine for disease, most commonly colorectal cancer. Everyone aged 50 and over should be screened for colorectal cancer. Endoscopy can be helpful in the evaluation or diagnosis of various problems, including difficult or painful swallowing, pain in the stomach or abdomen, bleeding, ulcers, tumors, and problems with the gallbladder, pancreas, and bile ducts.