The Respiratory System
Breathing, controlled by the respiratory system, is a continuous process of which a person is normally unaware. If breathing stops, however, a person becomes acutely aware of the fact. An individual can go days without food and water and hours without sleep, but only five or six minutes without air. Anything beyond that would be fatal. The trillions of cells in the body need a constant and generous amount of oxygen to carry out their vital functions. As they use that oxygen, they give off carbon dioxide as a waste product. It is the role of the respiration system, working in conjunction with the cardiovascular system, to supply the oxygen and dispose of the carbon dioxide.