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Author(s): David R. Caprette, PhD
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The Science of Breathing (cont.)

When air enters the lungs, oxygen is exchanged between the atmosphere and blood. The cells of our body require oxygen to complete the reactions that allow energy to be released from food. This process, known as aerobic respiration, produces carbon dioxide. 

Air enters the body through the nose, where it is warmed and filtered. It travels down the throat and trachea, and into the chest cavity, where the trachea branches into bronchi. Bronchi branch into many alveoli, which are surrounded by very small blood vessels. This allows oxygen to move into the bloodstream and carbon dioxide to move out of the bloodstream.