Epithelial lining of respiratory bronchiolus in the lung (gerbil)

Electron microscopy (low magnification). Two major cell types line a bronchiolus: a cuboidal-shaped ciliated one that exhibits microvilli with many organelles (1); the non-ciliated cells (2, Clara cells) are taller and are well provided with numerous electron-grey and smaller electron-dense secretory granules containing a mixture of cholesterol and glycosaminoglycans. When released onto the surface they probably provide a protective layer. (3) shows a small pulmonary artery with erythrocytes. At (*) sarcoplasm of smooth muscle cells