By Parveen Kumar, DBE, BSc, MD, DM, DEd, FRCP, FRCP(L&E), FRCPath, FIAP, Professor of Medicine & Education, Barts and The London School of Medicine and Dentistry, Queen Mary, University of London, and Honorary Consultant Physician and Gastroenterologist, Barts Health NHS Trust and Homerton Hospital NHS Foundation Trust, London, UK and Michael L Clark, MD, FRCP, Honorary Senior Lecturer, Barts and The London School of Medicine and Dentistry, Queen Mary,University of London and Consultant Physician, Princess Grace Hospital, London, UK Enhanced e-book accompanies the print book, for ease of transportation and use on the move