Endoscopy is when an endoscope is used to examine the intestinal or respiratory tract. An endoscope is an instrument with long glass fibres that allow the user to see into a body part not visible from the outside. The oesophagus, stomach, lung and large intestine are all accessible with the use of an endoscope. The surface of the intestinal tract is visible and it can help clinicians to decide if tissue sampling or further surgery is warranted. Fluid and tissue samples can be taken from deep in the lungs.