The respiratory segment constitutes most of the volume of the nasal cavities. It is lined with a ciliated, pseudostrati-fied columnar epithelium. The underlying lamina propria is attached to the periosteum of the adjacent bone.
The medial wall of the respiratory segment, the nasal septum, is smooth, but the lateral walls are thrown into folds by the presence of three shelf-like, bony projections called turbinates or conchae. The turbinates play a dual role. They increase surface area as well as cause turbulence in airflow to allow more efficient conditioning of inspired air.
The ciliated, pseudostratified columnar epithelium of the respiratory segment is composed of five cell types:
• Ciliated cells, tall columnar cells with cilia that project into the mucus covering the surface of the epithelium
• Goblet cells that synthesize and secrete mucus
• Brush cells, a general name for those cells in the respiratory tract that bear short, blunt microvilli conchae nasal mucosa vestibule hard palate soft palate-
— nasopharynx vestibule hard palate soft palate-
— nasopharynx esophagus hyoid bone cricoid cartilage-trachea
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