The process of breathing (respiration) is divided into two phases: Inspiration (Inhalation) & Expiration (Exhalation). During Inspiration, the diaphragm contracts, increases the size of the thoracic cavity and decreases the pressure inside. As a result, air rushes in and fills the lungs. During Expiration, the diaphragm relaxes, decreases the size of the thoracic cavity, and increases the pressure inside. As a result, the lungs contract and air is forced out.

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