Respiratory system

The organs responsible for carrying oxygen from the air to the blood and expelling carbon dioxide. The upper part of the respiratory system consists of 2 nasal passages; the pharynx; the larynx (which contains the vocal cords); and the trachea. The lower part of the respiratory tract consists of two lungs, which are enclosed in a double membrane called the pleura, and the lower airways (the bronchi and smaller bronchioles). These structures are encased and protected by the bony ribcage. The airways terminate in millions of balloon-like sacs known as alveoli, where gas exchange with the tiny blood vessels surrounding them takes place. These small vessels feed into larger pulmonary vessels for blood transport to and from the heart. Air is inhaled and exhaled (see breathing) by the action of the dome-shaped diaphragm and of abdominal and chest muscles including the intercostal muscles between the ribs.


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