The human respiratory system consists of a series of organs that form a passageway for the air flowing to and from the alveoli of the lungs. The lungs themselves are discrete organs of the body containing the alveoli and are located in individual serous cavities.

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The air passageway can be conveniently divided into three groups of structures. The larynx is the central portion. The other organs are grouped as supra laryngeal or infra-laryngeal.

The general functions of the supra laryngeal structures are to condition the in flowing air and to test it. Conditioning includes cleansing, warming, and moistening.