Process of taking in air for oxygen and releasing it to dispose of carbon dioxide. The amount of air inhaled and exhaled in an average human breath (tidal volume) is about one-eighth the amount that can be inhaled after exhaling as much as possible (vital capacity). Nerve centres in the brain regulate the movements of muscles of respiration (diaphragm and chest wall muscles). Blood in the pulmonary circulation brings carbon dioxide from the tissues to be exhaled and takes up oxygen from the air in the pulmonary alveoli to carry it to the heart and the rest of the body. Because the body stores almost no oxygen, interruption of respiration—by asphyxiation, drowning, or chest muscle paralysis—for more than a few minutes can cause death. Disorders affecting respiration include allergy, asthma, bronchitis, emphysema, pneumonia, and tuberculosis. See also respiratory system; respiratory therapy.

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