ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY
Light micrograph of lung tissue showing alveolar sacs (large white areas) and alveoli (smaller and round). Histological sections of lung tissue only show the walls of these structures as thin aggregations of smooth muscle cells and connective tissue, which is formed by collagen and elastic fibres. This network is also occupied by capillaries which are supplied by larger pulmonary vessels. In the alveoli the epithelium of the capillaries is directly applied to the alveolar wall. This arrangement provides an interface of minimal thickness between alveolar air and blood. Magnification: x25 at 35mm size.
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