Beyond Basics
Gastrointestinal Physiology: An Overview
The gastrointestinal (GI) tract is the segment of the
digestive system that begins at the mouth and ends at the anus. It is
made up of the esophagus, stomach, small intestine, and colon (Fig. 1).
Figure 1 –
The Digestive Tract with Detail of Lower GI Tract
The main function of the GI tract is to take in nutrients
and eliminate wastes. It is remarkably efficient: less than 5% of the
nutrients in the foods we eat (carbohydrate, protein, fat, vitamins, and
minerals) is excreted in the feces of healthy adults. By adding water,
ions, and enzymes, the GI tract changes food into a solution of molecules
that can be absorbed and transported into the bloodstream. The GI tract
is so efficient that the majority of substances added by the body to aid
the digestive process (e.g., bile acids) are absorbed for reuse.
The functions of the different parts of the GI tract
are integrated and coordinated by control mechanisms that involve numerous
neural and chemical stimuli, and are finely tuned to respond to the nutrients
present in specific foods. Many of these functions are impaired in patients
who have had parts of their small intestine and/or colon surgically removed.
This information
is provided as a general educational service
and is not intended to recommend any particular treatment plan
or to replace the advice of physicians. It is important that patients
seek and rely on the advice of a healthcare professional
about their individual medical conditions.
