A flexible tube called an endoscope is used to view different parts of the digestive tract. The tube contains several channels along its length. The different channels are used to transmit light to the area being examined, to view the area through a camera lens (with a camera at the tip of the tube), to pump fluids or air in or out, and to pass biopsy or surgical instruments through. When passed through the mouth, an endoscope can be used to examine the esophagus, the stomach, and some of the small intestine. When passed through the anus, an endoscope can be used to examine the rectum, anus, and the entire large intestine. Different endoscopes are used for different procedures, and the tubes vary in length and size.