The human respiratory system consists of two main parts: the airway (nose, mouth, trachea, lungs) and the muscles involved in breathing, including the diaphragm muscle, which is located between the lungs and abdomen. It plays the most important role in inhalation. When the diaphragm contracts and moves down, the lungs expand, the pressure is more negative, causing air to flow into the airway (inhalation). When the diaphragm relaxes and pushes up, the lungs contract, causing air to flow out of the airway (exhalation).
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