In the respiratory system, the lungs exchange waste carbon dioxide of blood for fresh oxygen. The upper respiratory tract includes the nose, nasal cavity, paranasal sinuses, pharynx, and larynx. The lower respiratory tract begins at the trachea and includes the bronchi and lungs.
Respiration is the exchange of oxygen and carbon dioxide between the atmosphere and the tissues. It has three components. Ventilation (breathing) exchanges gases between the atmosphere and the air sacs (alveoli) of the lungs. It occurs in the conducting portion of the respiratory system. External respiration is the exchange of fresh oxygen for waste carbon dioxide in the alveoli. Internal (tissue) respiration is gas exchange at the level of the tissues.
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