Nasal cavity

Cavitas nasi

Also known as: nose, nasal fossa

Paired air passages from the nostrils to the choanae, divided by the nasal septum and enlarged by the conchae, which warm, humidify and filter inspired air and house the organ of smell.

Show on body map Respiratory Tract

Overview

Length (naris to choana)≈7–8 cm

Air leaving nose≈37 °C, near 100% humidity

Share of airway resistance (nasal breathing)up to ≈50%

Each half of the nasal cavity extends from the naris anteriorly to the choana (posterior nasal aperture), where it opens into the nasopharynx. The roof is narrow (nasal, frontal, cribriform plate of the ethmoid, sphenoid), the floor is the hard palate, the medial wall is the nasal septum and the lateral wall carries three scroll-like conchae (turbinates) that overhang the meatuses into which the paranasal sinuses and nasolacrimal duct drain.

Three regions are recognised: the skin-lined vestibule; the respiratory region (most of the cavity), lined by pseudostratified ciliated columnar epithelium with goblet cells over a highly vascular lamina propria with venous cavernous (erectile) plexuses; and the olfactory region in the roof (≈ upper 1 cm, superior concha and upper septum). The conchae create turbulent airflow that throws particles onto mucus and maximise contact with warm, moist mucosa, so air reaching the pharynx is near 37 °C and almost saturated with water vapour. The venous plexuses of the conchae engorge alternately every few hours (the nasal cycle).

Location: Above the hard palate, below the anterior cranial fossa, medial to the orbits and maxillary sinuses.

Parts & subdivisions

Vestibule
Skin-lined entrance with vibrissae.
Respiratory region
Pseudostratified ciliated columnar epithelium, goblet cells, seromucous glands and cavernous venous plexuses.
Olfactory region
Olfactory epithelium in the roof; bipolar receptor neurons pass through the cribriform plate as olfactory nerve fibres.
Conchae and meatuses
Superior, middle and inferior conchae with the meatuses beneath them; spheno-ethmoidal recess above the superior concha.
Choanae
Posterior apertures opening into the nasopharynx.

Anatomy

Innervation: General sensation: CN V1 (anterior ethmoidal nerve) and CN V2 (nasopalatine and posterior superior lateral nasal nerves). Special sense: olfactory nerve (CN I). Secretomotor parasympathetic fibres from the facial nerve (greater petrosal nerve → pterygopalatine ganglion); sympathetic vasoconstrictor fibres from the superior cervical ganglion.
Arterial supply: Branches of the maxillary artery (sphenopalatine — the main supply — and greater palatine), the ophthalmic artery (anterior and posterior ethmoidal) and the facial artery (septal branch of the superior labial and lateral nasal).
Venous drainage: Rich submucosal venous plexus draining to the sphenopalatine, facial and ophthalmic veins (connections with the cavernous sinus).
Lymphatic drainage: Anterior part → submandibular nodes; posterior part → retropharyngeal and upper deep cervical nodes.
Relations: Superiorly the anterior cranial fossa (cribriform plate); laterally the orbits and maxillary sinuses; inferiorly the oral cavity; posteriorly the nasopharynx.
Histology: Respiratory mucosa: pseudostratified ciliated columnar epithelium with goblet cells, a thick basement membrane and a lamina propria containing seromucous glands, lymphoid tissue and thin-walled venous sinusoids. Olfactory mucosa: tall pseudostratified epithelium of olfactory receptor neurons, sustentacular cells and basal stem cells, with Bowman's glands.

Function

Conducts air to the pharynx; preferred breathing route at rest.
Warms, humidifies and filters inspired air (particles > ≈10 µm are trapped).
Houses the olfactory epithelium (smell).
Acts as a resonating chamber for speech.
Receives drainage from the paranasal sinuses and nasolacrimal duct.

Clinical significance

Epistaxis

≈90% of nosebleeds arise anteriorly from Kiesselbach's plexus (Little's area) on the anterior septum, where branches of the anterior ethmoidal, sphenopalatine, greater palatine and superior labial arteries anastomose; most settle with firm pressure on the soft nose. Posterior bleeds (sphenopalatine territory, often in older hypertensive patients) are heavier and may need posterior packing or arterial ligation/embolisation.

CSF rhinorrhoea

A fracture of the cribriform plate can tear the dura, allowing clear CSF to leak from the nose (positive for β2-transferrin), with risk of meningitis; it may be accompanied by anosmia.

Rhinitis and nasal polyps

Allergic rhinitis is IgE-mediated mucosal inflammation. Nasal polyps in adults are associated with asthma and aspirin sensitivity (aspirin-exacerbated respiratory disease); in children they should prompt testing for cystic fibrosis.

Test yourself

Into which part of the nasal cavity does the maxillary sinus drain?

Middle meatus via the semilunar hiatus
Inferior meatus
Superior meatus
Sphenoethmoidal recess

Answer: Middle meatus via the semilunar hiatus

The maxillary ostium opens high on the medial wall of the sinus into the semilunar hiatus of the middle meatus — a poor position for gravitational drainage, which helps explain why maxillary sinusitis is common. The inferior meatus receives the nasolacrimal duct.