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The respiratory system includes the nasal passages, pharynx, larynx, trachea, and lung. The epithelium of the nasal passages is of the pseudostratified, ciliated columnar type with numerous goblet cells. The nasal passages also contain olfactory epithelium, including specialized bipolar nerve cells supported by two cell types, basal and supporting cells. The supporting cells form tall columns of cells with oval nuclei near the surface; many olfactory nerve cells are subjacent. The olfactory cells are bipolar ganglion cells, the apical portion forming a dendrite that extends to the surface as a base for nonmotile cilia. Below the nucleus the cytoplasm extends to a fine thread to form an unmyelinated axon that eventually constitutes, along with others, the olfactory nerve bundles. Basal cells are roughly triangular and are seen between other cells along the basement membrane. Glands in the interstitial tissue membrane are the tubuloalveolar type (mucous and serous).