The insertion tube of the endoscope is a major differentiating feature among endoscopes designed for gastroenterology. Although obvious differences exist depending on the application of the endoscope (e.g., the extra-long length of the endoscope, the thinness of a transnasal esophagoscope), the subtler differences between endoscope models are just as important. This is especially true for colonoscopes; although endoscopists may prefer using a particular colonoscope model for various reasons, the instrument’s insertion tube characteristics more than anything else likely cause an endoscopist to pick a particular colonoscope as the instrument of choice. If any single specification of the instrument can determine the speed and ease with which the endoscopist can insert the instrument, it is the mechanical characteristics of the insertion tube.

Endoscope manufacturers have put significant effort into refining the construction of the insertion tube and selecting ideal materials. The insertion tube usually contains (1) tubes for suction (biopsy), air, and water feeding; (2) often an additional tube for a forward water jet; (3) four angulation control wires; (4) fine electrical wires connecting the charge-coupled device (CCD) image sensor at the distal tip of the endoscope to the video processor; and (5) delicate glass fibers for bringing light from the light source to the distal end of the endoscope. Colonoscopes with adjustable insertion tube flexibility have an additional component—a tensioning wire to control insertion tube stiffness. Duodenoscopes also have an additional wire/coil sheath running the length of the insertion tube for controlling the up-and-down position of the forceps elevator.