Illustration copyright 2000, 2004 by Nucleus Communications, Inc. All rights reserved. http://www.nucleusinc.com

The main function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing.

The upper respiratory tract (upper airway) consists of the nose, mouth, sinuses, pharynx (upper section of the throat), and larynx (voice box). The lower respiratory tract consists of the trachea (windpipe), bronchial tubes, and lungs. The bronchial tubes carry air into the lungs and branch into smaller and smaller bronchioles. These end in alveoli (air sacs).