Digestive System Overview
What is digestion?
Food and drink must be changed into smaller molecules of nutrients to be absorbed
into the blood and carried to cells throughout the body. Digestion is the process
by which food and liquid are broken down into smaller parts so that the body can use
them to build and nourish cells, and to provide energy.
How does the digestive process work?
Digestion begins in the mouth, where food and liquids are taken in, and is completed
in the small intestine.
What is included in the digestive system?
The digestive system is made up of the digestive tract and other organs that aid in
The digestive tract is a series of hollow organs joined in a long, twisting tube from
the mouth to the anus, consisting of the following:
Organs that help with digestion, but are not part of the digestive tract, include
Parts of other organ systems, such as nerves and blood, also play a major role in
the digestive process.
How does food move through the digestive system?
In a wave-like movement, called peristalsis, muscles propel food and liquid along the digestive tract. In general, there are
6 steps in the process of moving food and liquid through the digestive system:
The first major muscle movement is swallowing food or liquid. The start of swallowing
is voluntary, but once it begins, the process becomes involuntary and continues under
the control of the nerves.
The esophagus connects the throat above with the stomach below. It is the first organ
into which the swallowed food goes.
Where the esophagus and stomach join, there is a ring-like valve that closes the passage
between the 2 organs. When food nears the closed ring, the surrounding muscles relax
and allow the food to pass into the stomach, and then it closes again.
The food then enters the stomach. This completes 3 mechanical tasks: stores, mixes,
First, the stomach stores the swallowed food and liquid. This needs the muscle of
the upper part of the stomach to relax and accept large volumes of swallowed material.
Second, the lower part of the stomach mixes up the food, liquid, and digestive juices
made by the stomach by muscle action.
Third, the stomach empties the contents into the small intestine.
The food is digested in the small intestine and dissolved by the juices from the pancreas,
liver, and intestine. The contents of the intestine are mixed and pushed forward to
allow further digestion.
Last, the digested nutrients are absorbed through the intestinal walls. The waste
products, including undigested parts of the food, known as fiber, and older cells
that have been shed from the mucosa, move into the colon. Waste products in the colon
usually remain for a day or two until the feces are expelled by a bowel movement.
Online Medical Reviewers:
- Adler, Liora C, MD
- Freeborn, Donna, PhD, CNM, FNP