The respiratory system, including the lungs, brings air into the body. The oxygen in the air travels from the lungs through the bloodstream to the cells in all parts of the body. The cells use the oxygen as fuel and give off carbon dioxide as a waste gas. The waste gas is carried by the bloodstream back to the lungs to be eliminated or exhaled. The lungs accomplish this vital process - called gas exchange - using an automatic and quickly adjusting control system.