ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
Healthy lungs. Computer graphic of a healthy pair of human lungs, sectioned to show the internal anatomy of airways. At upper centre, the trachea (windpipe) introduces air from the larynx of the throat into the respiratory system. The trachea branches into two bronchi before entering each lung. Within the lungs the bronchi divide into an internal network of smaller and finer bronchioles. These bronchiole tubules finally end in tiny air sac alveoli (not seen). In alveoli, exchange of gases occurs: inhaled oxygen enters the blood and carbon-dioxide is breathed out. For this respiration process, the lungs are inflated and deflated by movement of the diaphragm and ribs.
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