How The Gut Works: Digestive Disorders

Content provided by the Faculty of the Harvard Medical School

How the gut works

The "gut." It's an ancient Anglo-Saxon word that refers to the human digestive system. Think of this marvel of nature's engineering as a perpetual food processor, constantly mixing, grinding, and transforming the meats, vegetables, fruits, and snacks that people eat into biologically useful molecules.

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 (see Figures 1 and 2). 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.

Figure 2: How long does it take? The time it takes for food to pass through all sections of the digestive tract can be anywhere from 9 hours to over 3 days.

The organs of the gut are almost always moving, driven by muscles in the wall of the gut. 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 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" (meaning dissolvable in water) so that nutrients can be easily absorbed into the bloodstream.

Last updated:	August 21, 2007