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When you breathe in the diaphragm moves down. This increases the volume of the thorax (chest) and lungs, which reduces the pressure of air in the lungs. Air enters when the pressure in the lungs falls below that in the atmosphere. When you breathe out the diaphragm moves up, reducing the volume in the lungs and increasing the pressure. When the pressure in the lungs is greater than that of the atmosphere air leaves the lungs.

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17y ago

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