Gastroenterology is a branch of medicine that focuses on the digestive system and its disorders. Diseases that affect the gastrointestinal tract, including organs from the mouth to the anus, near the alimentary canal, are the focus of this specialty. The doctors who practice this profession are called gastroenterologists. They usually complete about eight years of pre-medical and medical education, an annual internship (if this is not part of the residency), three years of internal medicine experience, and three years in gastroenterology fellowships. Gastroenterologists perform many diagnostic and therapeutic procedures including colonoscopy, esophagogastroduodenoscopy (EGD), endoscopic retrograde cholangiopancreatography (ERCP), endoscopic ultrasound (EUS), and liver biopsy. Some gastroenterology professionals will complete the "fourth year" (although this is usually their seventh year of doctoral studies) in transplant hepatology, advanced endventional endoscopy, inflammatory bowel disease, motor function, or other topics.