The human respiratory system from the openings of the mouth and nose to the myriad components of the lungs begins functioning within moments of birth. From that time on, the respiratory system supplies the body with the oxygen it needs to survive. It accomplishes this task by bringing clean, filtered air to the lungs, where oxygen is absorbed into the circulatory system. The lungs also remove used air, eliminate impurities, and enable us to speak. With luck and some care, these crucial organs will serve a long lifetime.
Air enters the respiratory system when the chest expands.
If the chest cavity is punctured and opened to the outside world, the lungs collapse. Under normal conditions, this is prevented by the protection of the rib cage and the chest wall muscles and diaphragm. There, oxygen is absorbed and waste gases are expelled as the lungs retract or deflate to their original size. Within the breathing passages, air is further filtered and inhaled impurities are trapped by mucus a sticky fluid produced by tiny gland cells in the passage linings. Mucus also moistens the air so that the delicate tissues of the lungs will not be dried by the airflow.