All the cells of the body need oxygen in order to carry out their metabolism. Oxygen reacts with nutrients inside the cells to produce the energy needed to fuel the cells’ activities.

Carbon dioxide is produced as a waste product of these reactions and must be removed if the cells are to continue to function efficiently.

The exchange of oxygen and carbon dioxide between the cells of the body and the environment is called respiration and the body system that is responsible for introducing oxygen into the blood and removing carbon dioxide from the body is the respiratory system.