MANFRED KAGE / SCIENCE PHOTO LIBRARY. MANFRED KAGE / SCIENCE PHOTO LIBRARY.
Light micrograph of a section of normal human lung tissue, showing the smooth muscle & connective tissue walls of alveolar ducts and sacs (alveoli), and (centre), a bronchiole. Bronchioles form the small branches of a tree of airways that conducts air from the trachea (windpipe) into the bronchi, dividing many times into numerous bronchioles in each lung. The bronchial wall is covered by a simple epithelial layer of ciliated columnar cells (red), supported by a layer of smooth muscle (stained black). Bronchioles divide into alveolar ducts and alveoli, where gaseous exchange occurs through surrounding blood capillaries. Magnification: X160 (6x7cm), X70 (35mm).
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