Nearly 30 feet long if stretched out straight, the gut is a series of hollow organs linked to form a long, twisting tube that runs from the mouth to the anus. This string of organs is known as the alimentary canal, gastrointestinal (GI) tract, or digestive tract. It comprises the esophagus (or gullet), stomach, small intestine, and colon (which includes the rectum). These organs break down food and liquids -- carbohydrates, fats, and proteins -- into chemical components that the body can absorb as nutrients and use for energy or to build or repair cells. What's left is expelled by a highly efficient disposal system.
The organs of the gut are almost always moving, driven by muscles in their walls. These muscles consist of an outer longitudinal layer and an inner circular layer. The coordinated contractions of these layers push food and fluids the length of the canal, just as rolling waves deposit sand and shells on the shore. This dynamic movement along the gastrointestinal tract is known as peristalsis.
Helping with the job of digestion is the mucosa, or lining, of the mouth, stomach, and small intestine, which harbors glands that produce digestive enzymes. The salivary glands, liver, and pancreas also secrete juices that help make food soluble (dissolvable in water) so that nutrients can pass easily into the bloodstream.