Epithelial lining of bronchiolus in the lung (mammalia)

Scheme electron microscopy. Two major cell types line a bronchiolus, a more cuboidal shaped ciliated one (1) that also exhibits microvilli with many organelles (including electron-dense lysosomal structures). The non-ciliated cells (2, Clara cells) appeared taller and dome-shaped and protrude into the lumen. These cells are well provided with organelles, the apical portion shows Golgi areas and numerous electron-dense secretory granules containing a mixture of cholesterol and glycosaminoglycans. When released onto the surface they probably provide a protective layer. On the basal lamina (3) a small neuroendocrine cell (4) (belonging to the Amine Precursor Uptake and Decarboxylation cell system so-called APUD cells). The dense-core granules contain among others dopamine or serotonin.