Lung anatomy. Computer illustration of the trachea and bronchi network of the human lungs. At top is the larynx (voice box) through which air enters the trachea (windpipe, upper centre). The trachea branches into two bronchi which enter the pair of lungs. Both the trachea and the bronchi are strengthened with rings of cartilage. Within the lungs, the bronchi divide into an internal network of smaller and finer bronchioles (pink). These bronchiole tubes end in tiny air sacs called alveoli. In the alveoli, gases are exchanged: inhaled oxygen enters the blood and carbon dioxide is breathed out.
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