An endoscope is a medical device that allows doctors to view the inside of a persons body. It is composed of an image sensor, optical lens, light source, and mechanical device, and is inserted through a natural opening such as the mouth or anus. The device uses modern technologies such as optics, ergonomics, precision mechanics, electronics, and software engineering to observe lesions that cannot be detected by X-ray, making it useful in medical diagnosis. Endoscopes use tubes that are only a few millimeters thick to transfer illumination in one direction and high-resolution images in real-time in the other direction, resulting in minimally invasive surgeries. During an endoscopy, the doctor inserts a tool called an endoscope into a persons body, which is a thin tube with a powerful light and tiny camera at the end. The endoscopes length and flexibility depend on the part of the body the doctor needs to see. For example, a straight endoscope helps a doctor look at joints, while a flexible one helps a doctor view the inside of the colon. An endoscopy offers an opportunity to collect tissue samples (biopsy) to test for diseases and conditions that may be causing anemia, bleeding, inflammation, or diarrhea. It can also detect some cancers of the upper digestive system. Special tools can be passed through the endoscope to treat problems in the digestive system, such as burning a bleeding vessel to stop bleeding, widening a narrow esophagus, clipping off a polyp, or removing a foreign object. There are many types of endoscopy, each designed for looking at a certain part of the body.