- published: 04 Apr 2012
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The human lungs are the organs of respiration in humans. Humans have two lungs. Together, the lungs contain approximately 2,400 kilometres (1,500 mi) of airways and 300 to 500 million alveoli, having a total surface area of about 70 square metres (750 sq ft) (8,4 x 8,4 m) in adults — roughly the same area as one side of a tennis court. Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 992 kilometres (616 mi). Each lung weighs 1.1 kilograms (2.4 lb), therefore making the entire organ about 2.3 kilograms (5.1 lb).
The conducting zone contains the trachea, the bronchi, the bronchioles, and the terminal bronchioles The respiratory zone contains the respiratory bronchioles, the alveolar ducts, and the alveoli. The conducting zone and the respiratory stuffers (but not the alveoli) are made up of airways. The conducting zone has no gas exchange with the blood, and is reinforced with cartilage in order to hold open the airways. The conducting zone warms the air to 37 °C (99 °F) and humidifies the air. It also cleanses the air by removing particles via cilia located on the walls of all the passageways. The lungs are surrounded by the rib cage. The respiratory zone is the site of gas exchange with blood.
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