Normally, as food moves along the digestive tract,
digestive juices and enzymes digest and absorb calories and nutrients
(see figure 1). After we chew and swallow our food, it moves down the
esophagus to the stomach, where a strong acid continues the digestive
process. The stomach can hold about 3 pints of food at one time. When
the stomach contents move to the duodenum, the first segment of the
small intestine, bile and pancreatic juice speed up digestion. Most of
the iron and calcium in the foods we eat is absorbed in the duodenum.
The jejunum and ileum, the remaining two segments of the nearly 20 feet
of small intestine, complete the absorption of almost all calories and
nutrients. The food particles that cannot be digested in the small
intestine are stored in the large intestine until eliminated.