Which procedure involves the passage of a small camera through the distal gastrointestinal tract?

The procedure that involves the passage of a small camera through the distal gastrointestinal tract is colonoscopy. During a colonoscopy, a long, flexible tube with a camera and light is inserted through the rectum and navigated through the entire colon. This allows for direct visualization of the colon's inner lining, which is essential for diagnosing various conditions, including polyps, inflammatory bowel disease, and cancer.

In this context, the term "distal gastrointestinal tract" specifically refers to the lower part of the GI tract, including the rectum and colon. While endoscopy encompasses a wider range of procedures involving camera insertion into the gastrointestinal tract, including upper GI scopes, it does not specifically pinpoint the distal aspect. Sigmoidoscopy is another procedure that involves examining the lower part of the colon, but it only goes up to the sigmoid colon and does not cover the entire length of the colon as colonoscopy does. Gastroscopy, on the other hand, involves examining the upper gastrointestinal tract, including the esophagus, stomach, and duodenum, which does not pertain to the distal gastrointestinal tract.

Thus, colonoscopy is the most precise answer when discussing the investigation of the distal gastrointestinal tract.