BSIP ESTIOT / SCIENCE PHOTO LIBRARY BSIP ESTIOT / SCIENCE PHOTO LIBRARY
Breathing. Illustration of a woman's upper body showing the exhalation of air from her respiratory system. Carbon dioxide continually diffuses from the blood of tiny capillaries into the alveoli, or air sacs, of the lung. The path of this carbon dioxide out of the body is depicted by the yellow arrows. Waste air travels from the alveoli into bronchioles which merge and grow ever larger, forming bronchi (in lung at right). These smaller bronchi eventually lead to the main bronchus of each lung which meet to form the tubular trachea, or windpipe (at centre). Finally waste air is expelled from the nose or mouth. Fresh air reaches the lungs by the reverse path.
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