a. Definition. The human digestive system is a group of organs designed to take in foods, initially process foods, digest the foods, and eliminate unused materials of food items. It is a hollow tubular system from one end of the body to the other end. See figure 6-1.

Figure 6-1. The human digestive system.

b. Major Organs. The major organs involved in the human digestive system are listed below. They are each discussed later in this lesson.


Mouth or oral complex.








Small intestines and associated glands


Large intestines.




Anal canal and anus.

c. Digestive Enzymes. A catalyst is a substance that accelerates (speeds up) a chemical reaction without being permanently changed or consumed itself. A digestive enzyme serves as a catalyst, aiding in digestion. Digestion is a chemical process by which food is converted into simpler substances that can be absorbed or assimilated by the body. Enzymes are manufactured in the salivary glands of the mouth, in the lining of the stomach, in the pancreas, and in the walls of the small intestine.

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