BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY
Bronchiole of lung. Light micrograph of a cross section through a bronchiole in the lung. A bronchiole is a small air passage (at centre). It is lined with a ciliated columnar epithelium (black, folded); the outer pink ring is the smooth muscle layer. A bronchiole controls air flow within the lungs by adjusting the diameter of the air passage (white, centre). Surrounding the bronchiole are the smaller air passages, the alveoli (spongy appearance) into which the bronchioles open. These are lined with epithelium (pink) that is rich in capillaries so that gas exchange can take place. Stain and magnification unknown.
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