Title: Bronchiolus in the lung
Stain Azan, human. The lumen of the bronchiolus is lined with one layer of ciliated epithelium (1) and is folded due to the contraction of smooth muscle fibers (2) in the wall. Note the rich cellularity (3) in the stromal surrounding of the bronchiolus. Alveolar space (4).
(5) pulmonary artery branches.
Title: Epithelial lining of bronchiole in the lung
Scheme electron microscopy, human. 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.
Keywords/Mesh: respiratory tract, lung, bronchiole, smooth muscle, alveolus, ciliated epithelium, Clara cell, endocrine cell, APUD cell