Epithelial lining of trachea and bronchiolus (mammals)

Left side trachea: Columnar ciliated cells (1) with up to 200 motile cilia with an organelle-rich apex and in the middle a goblet cell (2) with accumulation of mucus secretion granules in the apex. Note that all epithelial cells (i.e., junctions) contact the basal lamina. Four basal cells (3) do not extend to the free surface, they are the stem cells for, among others, ciliated cells and goblet cells. Each population generally contribute about 30% of the total cell population. Endocrine cells (less than 10%) and brush cells are not depicted in this picture. Right side bronchiolus: Two major cell types line a bronchiolus, a more cuboidal shaped ciliated one (1) that also exhibit microvilli with many organelles (including electron-dense lysosomal structures). The non-ciliated cells (2, Clara cells) are taller and dome-shaped and protrude into the lumen. The Clara cells are also associated with release of Cl-ions (mediated by a chloride channel). 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. (See also image linked as a related resource.)