SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY SINCLAIR STAMMERS / 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 (upper centre). It is lined with a ciliated columnar epithelium (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 is cartilaginous tissue (pale, smooth appearance) providing structure for the lung. At bottom right are the alveoli (spongy appearance). It is into these smaller air passages that the bronchioles open and that gas exchange takes place. Magnification: x64 at 35mm size.
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