c. The majority of digestion in humans takes place in the small intestines. The
small intestines are located in the central part of the abdomen, immediately beneath the
abdominal wall. In healthy individuals, a flap called the greater omentum is draped over
the small intestines (between them and the anterior abdominal wall). The greater
omentum has a great deal of fat for insulation. It is richly supplied with blood vessels for
heat. Some might compare the greater omentum to an "electric blanket" for the small
Fatty Acids and Glycerol
Table 6-1. Foodstuffs, enzyme classes, and end-products of digestion.
6-17. DIGESTIVE ENZYMES
a. The digestive process begins in the oral cavity. The saliva contains enzymes
which initiate the digestion of complex carbohydrates.
b. In the stomach, the gastric glands produce enzymes that initiate the digestion
c. In the small intestines, there are digestive enzymes for all three classes of
foodstuffs--carbohydrates, lipids, and proteins. Enzymes for completing the digestion of
these three classes are found in the fluids produced by the pancreas and glands in the
mucosa of the small intestines. Moreover, there is a fluid called bile that is produced by
the liver and stored in the gallbladder for release into the small intestines. Bile helps in
the digestion of lipids.
d. The presence or absence of certain enzymes is genetically determined.
Therefore, some individuals may have difficulty digesting certain foods.
6-18. TIME AND LENGTH
The length of the small intestines appears to be just right. The time it takes for
material to travel from beginning to end is just about right for the completion of
The end-products of digestion are absorbed primarily through the walls of the