The respiratory system is responsible for taking in oxygen and expelling carbon dioxide. It can be divided functionally into two regions:

Conducting passages – convey air to the lungs while removing debris, warming, and humidifying the air (nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles)
Respiratory passages – where the exchange of gases between air and blood occurs (respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli)

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