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Overview of the Respiratory System

Author(s): Nancy Moreno, PhD, Barbara Tharp, MS, and Judith Dresden, MS.
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Human Respiratory System Diagram

Air (comprised primarily of nitrogen and only about 21% oxygen) enters the nose, where tiny hairs filter out dust and particles. Tissues moisten and warm the air, making it more suited for the lung environment. Air passes from the pharynx to the larynx (containing two elastic vocal cords) and into the trachea. The trachea divides into the left and right bronchi which subdivide into smaller and smaller tubes called bronchioles. These airways are lined by mucous membranes and countless cilia which trap and remove particles from the lungs. Bronchioles open into the alveoli which are clustered like grapes. Only one cell thick, alveoli have direct contact with capillaries for gas exchange. The grapelike arrangement of alveoli creates an enormous surface area sufficient for exchanging enough oxygen and carbon dioxide for the entire body.