Gastroscopy is the examination of the inner parts of the upper digestive system organs — the esophagus, stomach, and duodenum — using a special instrument called a gastroscope. The gastroscope is a flexible tube with a light source and a camera at its tip that captures images. It also has a working channel that allows the doctor to inspect the lining of the esophagus, stomach, and duodenum to detect any diseases or abnormal growths.