PHOTO INSOLITE REALITE / SCIENCE PHOTO LIBRARY PHOTO INSOLITE REALITE / SCIENCE PHOTO LIBRARY
False-colour scanning electron micrograph (SEM) of a section of the human lung, showing (centre) a bronchiole, one of the final divisions of a system of tubes (the bronchial tree) which conducts air to the millions of alveoli (air sacs) where gaseous exchange takes place. Bronchioles are divisions of the bronchial tree (the trunk of which is the trachea) which do not possess mucous secreting cells or cartilage in their walls. Bronchioles exist in different forms, the smallest of which are called terminal bronchioles; these open into an alveolar network via a short respiratory bronchiole. Magnification: X 30 at 35mm size.
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