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Your respiratory system provides the energy needed by cells of the body. Air is breathed in through the nasal cavity and/or mouth and down through the throat (the pharynx). The throat has three parts - the nasopharynx, the oropharynx, and the laryngopharynx. The air passes down the trachea (the windpipe), through the left and right bronchi, and into the lungs. Oxygen in the blood is delivered to body cells, where the oxygen and glucose in the cells undergo a series of reactions to provide energy to cells, and the waste product of this process is carried out of the lungs.

The larynx is your voice box; the epiglottis, a flap of cartilage that prevents food from entering the trachea; and the esophagus, the tube through which food passes to the stomach.

Parts of the respiratory system

Source: AMA's Current Procedural Terminology, Revised 1998 Edition. CPT is a trademark of the American Medical Association.