The external nose consists of a bony and cartilaginous framework. It is made of the frontal bone, nasal bones, maxilla bone, lateral cartilage, and alar cartilage. The nostrils, or anterior nares, are two external openings to the nasal cavity. Choanae, which are also called posterior naris, refer to two openings or apertures of the nasal cavity that open into the nasopharynx. It is the nasal septum that acts as a partition, dividing the nasal cavity into the right and left nasal cavities. Each of these cavities has a lateral wall, medial wall, roof, and floor. The nasal cavity is connected to the pharynx (throat) at the back. The eye sockets lie lateral to the nasal cavities. Paranasal sinuses, which are four pairs of air-filled spaces in the bones of the skull, are the extensions of the nasal cavity.
- Humidification of the inhaled air
- Filtration of dust
- Reception and drainage of secretions from the nasal mucosa, paranasal sinuses, and nasolacrimal ducts
Lined by the respiratory mucosa, the respiratory region is the largest part of the nasal cavity. On the surface of the respiratory mucosa is ciliated, pseudostratified columnar epithelium, which contains different types of cells. While the goblet cells secrete mucus, the ciliated cells perform the function of sweeping the dust and pathogens that are trapped in the mucus secreted by the goblet cells. The underlying lamina propria contains a vast vascular network. The inhaled air becomes warm, as blood flows through the capillary loops that lie close to the surface.
The nasal conchae provide large surface area, which allows the air to be warmed or humidified. Cilia are hair-like structures present in the respiratory epithelium. These help move the particulate matter towards the throat, from where it travels through the esophagus to the stomach.
- Vomer and the perpendicular plate of the ethmoid bone, which form the upper part
- Septal cartilage, which forms the anterior section
- Crest of the maxillary bone and palatine bone which form the lower part
- Superior meatus, which lies below the superior concha, receives the opening of the posterior, anterior, and middle ethmoid sinus.
- Middle meatus, which lies below the middle concha, receives the opening of the frontal sinus and maxillary sinus.
- Inferior meatus, which lies below the inferior concha, receives the opening of the nasolacrimal duct.
The paranasal sinuses are connected to the nasal cavity through small orifices called ostia. Sphenoethmoidal recess is a small area above the superior concha that receives the opening of the sphenoid sinus. Above the uppermost turbinate in both nasal cavities lies the olfactory region, which has a small area of about 2.5 cm2, and contains about 50 million specialized primary sensory receptor cells.