The gut, sometimes referred to as the alimentary canal or the gastrointestinal tract, is approximately nine meters long in the typical human adult. Although metabolism rates differ from person to person, food generally takes 18 to 20 hours to completely pass through the gut.

Extending from the mouth to the anus, the outer walls of the gut are composed of layers of muscle and tissue that undergo peristalsis, or waves of contraction, which push the food along its path. Individual sections of the gut have their own names, but are all part of the same digestive canal. From the mouth, the gut extends into the pharynx and the esophagus, which in turn convey food to the stomach. After being partially digested in the stomach, the food is passed on to the small and then large intestines, before excess waste exits the body.

Special units called goblet cells produce mucus to line the digestive tract. The mucus protects the inside of the gut from hard coarse food, allowing undigested items to easily glide through. The mucus membrane also keeps the stomach from self-digestion and acid damage and does not allow digestive enzymes to reach living cells in other parts of the body. A breakdown of the mucus layer can allow seepage of digestive materials and cause serious health problems.