Epithelium of trachea (mammals, common respiratory epithelium)

Scheme electron microscopy. 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 contributes about 30% of the total cell population. Endocrine cells (less than 10%) and brush cells are not depicted in this picture.