The nasal cavities are paired chambers separated by a bony and cartilaginous septum. They are elongated spaces with a wide base that rests on the hard and soft palate and a narrow apex that points toward the anterior cranial fossa. The skeletal framework of the nasal cavities is formed by bones and cartilages; most are located centrally in the skull except for the small anterior region that is enclosed within the external nose. Each cavity or chamber communicates anteriorly with the external environment through the anterior nares (nostrils), posteriorly with the nasopharynx through the choanae, and laterally with the paranasal sinuses and nasolacrimal duct, which drains tears from the eye into the nasal cavity (Fig. 19.2). The chambers are divided into three regions:  Nasal vestibule, which is a dilated space of the nasal cav ity just inside nostrils and lined by skin  Respiratory region, which is the largest part (inferior two-thirds) of the nasal cavities and lined by respiratory mucosa  Olfactory region, which is located at the apex (upper one- third) of each nasal cavity and lined by specialized olfac
Vestibule of the Nasal Cavity
The nasal vestibule forms a part of the external nose and communicates anteriorly with the external environment. It is lined with stratified squamous epithelium, a continuation of the skin of the face, and contains a variable number of vibrissae that entrap large particulate matter before it is carried in the air stream to the rest of the cavity. Sebaceous glands are also present, and their secretions assist in the entrapment of particulate matter. Posteriorly, where the vestibule ends, the stratified squamous epithelium becomes thinner and undergoes a transition to the pseudostratified epithelium that characterizes the respiratory region. At this site, sebaceous glands are absent.
trachea cricoid cartilage thyroid cartilage larynx epiglottis hyoid bone oral cavity soft palate hard palate vestibule nasal mucosa conchae olfactory mucosa choanae orifice of auditory tube nasopharynx oropharynx ventricular fold vocal fold esophagus laryngopharynx FIGURE 19.2 • Diagram of the relationship of the pharynx to the respiratory and digestive systems. The pharynx is divided into three parts: nasopharynx, oropharynx, and laryngopharynx. It is located posterior to the nasal and oral cavities and extends inferiorly past the larynx. The pharynx serves both respiratory and digestive systems. This midsagittal section also transects the cartilages forming the skeleton of the larynx (i.e., epiglottis, thyroid cartilage, and cricoid cartilage). Note the ventricular and vocal folds in the middle of the larynx, approximately at the level of the thyroid cartilage. This part of the larynx represents the narrowest portion of the respiratory system and is responsible for producing sound by audible vibration of the vocal folds.
Respiratory Region of the Nasal Cavity
The respiratory region constitutes most of the volume of the nasal cavities. It is lined by the respiratory mucosa that contains a ciliated, pseudostratified columnar epithelium on its surface. The underlying lamina propria is firmly attached to the periosteum and perichondrium of the adjacent bone or cartilage.
The medial wall of the respiratory region, the nasal septum, is smooth, but the lateral walls are thrown into folds by the presence of three shelf-like, bony projections called conchae or turbinates. The conchae divide each nasal cavity into separate air chambers and play a dual role. They increase surface area and cause turbulence in airflow to allow more efficient conditioning of inspired air.