a. Catabolism is a degenerative, energy-generating process. Complex
molecules of proteins, carbohydrates, and fats are systematically broken down into
simpler, smaller molecules by the body's cells. The bonding energies that hold the
atoms of a complex molecule together are released as the molecule is broken down.
Much of this energy released by catabolism is captured and stored by the cells in the
form of a chemical molecule known as ATP. Digestion is a catabolic process because
the breakdown of the food releases energy.
b. Anabolism is a building, energy-requiring process. New, more complex
molecules are synthesized from simple molecules. These larger molecules form the
body's structural and functional components. This synthesis requires the expenditure of
the cellular energy generated by the cell's catabolic activities.
THE DIGESTIVE SYSTEM
a. The digestive system is made up of the alimentary canal (food passageway)
and the accessory organs of digestion. The products of the accessory organs help to
prepare food for its absorption and use by the tissues of the body. The main functions
of the digestive system are:
To ingest and carry food so that digestion can occur.
To eliminate unused waste material.
b. The alimentary canal is approximately 28 feet long in the adult and extends
from the lips to the anus. It is composed of the organs listed below.
Mouth (and associated glands).
Small intestine (and associated glands).
Anal canal and anus.
c. Refer to figure 1-1, an illustration of the digestive system, as you continue to
read about the structure and function of each component.