ABSTRACT
The primary functions of the respiratory system are to deliver oxygen to the bloodstream where it can be routed throughout the body to every cell, and to remove the waste product of metabolism — carbon dioxide. Mitochondria within cells require oxygen to carry out oxidative phosphorylation, the series of reactions whereby energy contained in chemical bonds in food is repackaged into the bonds in the molecule ATP (a form of energy the cell can directly use). Although some cells in the body can function without oxygen for a short time, many cells (such as heart cells or brain cells) are absolutely dependent on an adequate supply of oxygen in order to survive. The respiratory system also plays a role in the process of speech, the defense of the body, and the regulation of body pH. It is also a rapid route by which volatile xenobiotics can reach the brain.
