← Back to Education · General GI
Basics of endoscopy
Scope types, what each part does, and the physics behind the view
What an endoscope is
An endoscope is a slender instrument with a light and a viewing system at its tip. It lets clinicians look inside a hollow organ or passage without open surgery. Flexible scopes bend to follow the body’s curves. Rigid tubes stay straight and give short, direct views.
Most scopes also contain channels for passing tools, moving air and water, and removing fluid. Those channels are what turn a scope from a camera into a procedure tool.
Common scope types
Grouped by the part of the tract they reach
| Scope | What it examines | Notes |
|---|---|---|
| Gastroscope (upper endoscope) | Esophagus, stomach, and the first part of the small intestine (duodenum) | Thin, roughly 9 to 10 mm across, with a working length near 1 meter. Used for biopsy, bleeding control, and treatments through its working channel. |
| Colonoscope | The full colon, and often the last part of the small intestine (terminal ileum) | Longer, with an insertion tube often about 1.3 meters or more, and wider at roughly 12 to 13 mm. Its shaft is more prone to looping. |
| Flexible sigmoidoscope | Rectum and sigmoid colon only | Shorter, around 60 cm. Covers only the lower colon. |
| Duodenoscope (side-viewing) | The duodenum, including the opening where the bile and pancreatic ducts drain | The camera faces sideways. Used for ERCP, which reaches the bile and pancreatic ducts. |
| Endoscopic ultrasound (EUS) scope | The gut wall and nearby organs | Has an ultrasound probe at the tip. Can guide needle sampling of nearby masses or lymph nodes. |
| Enteroscope | Deeper parts of the small intestine | Long and slender. Often used with a balloon-assisted overtube to help advance it. |
| Anoscope or proctoscope (rigid) | Anal canal and the lowest rectum | Short, straight tube for direct inspection and some simple treatments. |
| Capsule endoscopy (not a scope) | Small intestine, as the capsule passes through | A swallowed capsule with a camera. It moves passively through the gut and typically cannot be steered. |
Sizes are typical adult values. Models vary.
Parts of a flexible scope
The four main parts, plus the cord
- Control head: angulation knobs, valves, and the port for passing tools.
- Insertion tube: the long flexible shaft, with channels running inside.
- Bending section: the short segment near the tip that steers, moved by internal wires.
- Distal tip: the lens or sensor, the light, a washing nozzle, and openings for the channels.
The cord carries light, electrical signals, and the air, water, and suction tubing to the processor.
Inside the shaft
Cross-section of a typical insertion tube, not to scale
The physics, in plain terms
Light
Light travels down the shaft through bundles of thin glass or plastic fibers. Each fiber keeps light inside through total internal reflection: light that strikes the inner wall at a shallow angle bounces back in rather than escaping. Many newer scopes use LEDs instead, placed at the tip or in the processor.
Image
In a video scope, a small electronic sensor sits at the tip behind a lens. It converts light into electrical signals, which travel back through the cable, and the processor builds the picture. Older fiberscopes sent the image back through a bundle of fibers, with each fiber acting as one picture element.
Air: opening up the view
A pump in the processor pushes air through the air/water channel. Gentle inflation opens the folds of the bowel so the lining can be seen. Too much air causes cramping and bloating. Many units use carbon dioxide instead, because the body absorbs it much faster than room air, which tends to reduce bloating afterward.
Water: cleaning the lens and the lumen
Water uses the same channel as air and exits at a nozzle aimed at the lens. Activating the water function produces a jet that clears mucus and residue. Some units also use a dedicated irrigation pump during colonoscopy to wash away leftover fluid or stool.
Suction: removing fluid
A suction pump pulls fluid and gas back out through a channel. In most scopes, the working channel doubles as the suction route, so a tool inside it or thick debris reduces suction. Flow through a narrow tube drops off quickly as its diameter shrinks, which is why small changes in channel size matter.
Working channel: passing tools
A narrow tube runs the length of the shaft so accessories can reach the tip, such as biopsy forceps, snares, brushes, needles, and clip applicators. The accessory must fit the channel. Standard upper scopes typically have a channel of about 2.8 mm, and standard colonoscopes about 3.7 mm.
Angulation: levers and wires
Internal wires run along the shaft and attach near the tip. Each control knob turns a drum that pulls one wire while easing the opposite one, so the bending section curves toward the side that was pulled. It is a simple lever system. Friction along the shaft and tight bends in the body reduce how well the handle’s movement reaches the tip.
Torque and looping
Twisting the handle sends a turn down the shaft, but the long, curving path loses much of it to friction. In the colon, the shaft can form loops, and loops absorb both push and twist. Good technique focuses on reducing loops and straightening the path, not on forcing the scope forward.
Quick pre-use checks
Follow your unit’s protocol and the manufacturer’s instructions
- Light and image: confirm the light is even and the picture is steady on the screen.
- Angulation: move each knob through its full range in all four directions, and check for stiffness or slipping.
- Air and water: confirm both work, and that the water jet clears the lens.
- Suction: confirm it draws well when activated.
- Working channel: confirm it is clear and the port seals properly.
- Leak test and records: complete the leak test and reprocessing documentation that your policy requires.
Reprocessing and safety
Scopes are cleaned, disinfected to a high level or sterilized, leak tested, and dried between patients. Narrow channels can trap debris and moisture, so both thorough cleaning and thorough drying matter. Follow the manufacturer’s instructions and your infection-control policy at every step.
Key takeaways
- Match the scope to the target: gastroscope for the upper GI, colonoscope for the colon, and specialty scopes for ducts, ultrasound, and the small bowel.
- Light comes from fibers or LEDs. A sensor at the tip, or a fiber bundle, forms the picture.
- Air opens the view, water cleans it, and suction clears it. The working channel carries both tools and suction.
- Steering is a wire-and-lever system. Looping in the colon is what makes that system harder to use.
Educational overview only. Equipment specifications vary by manufacturer and model, so check the equipment manual and your unit’s policies before applying any detail here.
