Anatomy Of The Nasal Cavity Notes

Anatomy of the Nasal Cavity

The nares

N.B – nostrils (nares) are distinct from the nose, which is a distinct project from the face.

Nares are surrounded by hairless, sometimes modified skin. This modified region may be known as the nasolabial (cattle) or nasal (carnivores, small ruminants) plate. They are supported by nasal cartilages. Dorsal and lateral cartilages attach to the free end of the nasal septum, and form the shape of the opening.

In cattle, the nasolabial plate is formed of stratified, cornified epithelium. It is kept moist by watery secretion from nasolabial glands massed below the skin.

In horses, there is no ventral nasal cartilage, and the nostrils are very distensible. The supporting alar cartilages give a comma shaped nostril. There is also a dorsal ‘false’ nostril present. This occupies the nasoincisive notch, and leads to a blind nasal diverticulum.

In carnivores (dogs and cats) the nasal plate is divided by a median groove (philtrum) that continues ventrally to groove the upper lip. Secretions from the nasal gland keep the nasal plate moist. The nasal plate is covered with a thick keratinised epidermis.

Avian nares are slit-like openings. They are overhung by the operculum, a bony flap. There is wide communication between the nasal cavity and pharynx through the choana.

Pigs have small but highly sensitive nares on the end of their snout. The median septum contains a small bone, the os rostrale, in the pig.

The nasal cavity

1. Function

In addition to olfaction, the nasal cavity modifies incoming air before it is transported further down the respiratory tract. Air is warmed as it passes over the highly vascularised nasal conchae, humidified by the evaporation from nasal secretion and cleaned as it contacts the secretion from the mucus glands.

2. Nasal conchae and meatuses

There are two nasal cavities, divided by a median septum. Each nasal cavity is further divided into four meatuses by the nasal conchae.

The nasal conchae are scrolls of turbinate bone (arising from the ethmoid bone) that project into the nasal cavity. They are covered in nasal mucosa, underneath which is a layer of anastomosing blood vessels. They increase the respiratory surface area and create turbulence in the passing air. This helps to filter and warm or cool the air that passes.

The dorsal conchae originate from the ethmoid bone and attach to the maxilla, whilst the ventral conchae originate from the maxilla and extend further into the nasal cavity.

The common nasal meatus is the longitudinal space on either side of the nasal septum. Air flows through the common nasal meatus to the pharynx.

The dorsal meatus is the passage between the roof of the nasal cavity and the dorsal nasal concha. Air flows through the dorsal meatus to the olfactory mucosa.

The middle meatus is located between the dorsal and ventral nasal conchae, and communicates with the paranasal sinuses.

The ventral nasal meatus is positioned between the ventral nasal conchae and the floor of the nasal cavity. It is the main pathway for airflow leading to the pharynx.

3. Histology

Respiratory epithelium is pseudostratified, ciliated and columnar. It contains goblet cells which...

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