ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
Healthy lungs. Computer graphic of an outline of a pair of healthy human lungs. At upper centre the larynx (or voice box) is seen at the top of the trachea (windpipe). Air travels through the trachea into the two branching bronchi (at centre) and into each lung. The bronchi then divide into smaller and finer bronchioles (not seen). These end in microscopic alveoli where the exchange of gases takes place. Inhaled oxygen enters the blood and carbon dioxide is breathed out. For this process of respiration, the lungs are inflated and deflated by movement of the diaphragm and ribs.
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