Because of the stomach's capacity, the individual can engage in activities other
than eating. In addition, certain digestive processes are initiated in the stomach.
One way the stomach is adapted as a storage area is that its wall is quite
stretchable. Its lining has folds called rugae.
Another adaptation is that, at each end, there is a valve or similar structure to
keep contents from leaving. The "gastroesophageal valve" has not been demonstrated
anatomically. At the other end of the stomach is the well-developed pyloric valve.
The mucosal lining of the stomach contains a number of gastric glands. The
mixture produced by the stomach, called chyme, is quite acid.
The three layers of muscles help to ensure that the contents of the stomach are
Digestion occurs through the actions of chemicals called enzymes. The end
products (molecules or particles) are small enough to be absorbed through the walls of
Digestive enzymes are present to maintain the appropriate rates of reaction. A
catalyst is a substance that improves the rate of reaction without being consumed itself.
Digestive enzymes are catalysts. Without digestive enzymes, digestion would be too
slow to provide materials needed by the body. (para 6-16)
The majority of digestion in humans takes place in the small intestines. Draped
over these is a flap called the greater omentum. This flap has fat for insulation and
many blood vessels for heat. Thus, the greater omentum may be compared to an
The saliva contains enzymes that initiate the digestion of complex carbohydrates.
In the stomach, the gastric glands produce enzymes that initiate the digestion of
In the small intestines, there are digestive enzymes for carbohydrates, lipids, and
proteins. These enzymes are found in the fluids produced by the pancreas and glands
in the mucosa of the small intestines. Moreover, the liver produces a fluid called bile,
which is stored in the gallbladder for release into the small intestines; this fluid helps in
The absorptive area of the walls of the small intestines is increased by
permanent circular folds (plicae circulares) and by fingerlike processes called villi.