BSIP, GEMS EUROPE / SCIENCE PHOTO LIBRARY BSIP, GEMS EUROPE / SCIENCE PHOTO LIBRARY
Lungs. Coloured three-dimensional computed tomography (CT) scan of an axial section through the lungs. Numerous branching bronchi (airways, blue) are seen inside the lungs. The smaller branches (bronchioles) terminate in alveoli (not seen), air sacs where gaseous exchange takes place. At centre, the trachea can be seen splitting to form the two main bronchi, each of which leads to a lung. CT scans use beams of X- rays fired from different angles to build up images of internal structures. By combining the scans on a computer, 3-D images such as this can be built up.
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