Upper Airways Anatomy

The upper airway begins at the nasal cavity and extends to the larynx. It conditions inspired air by warming, humidifying, and filtering it before it reaches the delicate lower respiratory tract.

The nasal cavity is divided by the nasal septum, which is formed by the vomer bone posteriorly, the perpendicular plate of the ethmoid superiorly, and the septal cartilage anteriorly. The lateral walls of the nasal cavity bear three shelf-like projections called turbinates or conchae: the superior and middle conchae are processes of the ethmoid bone, while the inferior concha is an independent bone. Below each concha lies a meatus. The nasolacrimal duct drains into the inferior meatus. The paranasal sinuses drain into the middle meatus, making this the most clinically significant region.

The paranasal sinuses are air-filled cavities within the facial bones. There are four pairs: maxillary, frontal, ethmoid (multiple small cells), and sphenoid. They drain via ostia that are prone to obstruction during mucosal oedema, leading to sinusitis. The maxillary sinus ostium is located high on its medial wall, an unfavourable position that predisposes to poor drainage.

The pharynx is divided into three regions. The nasopharynx lies posterior to the nasal cavity and superior to the soft palate; it contains the pharyngeal tonsil (adenoids) and the openings of the Eustachian tubes. The oropharynx extends from the soft palate to the epiglottis and contains the palatine tonsils. The laryngopharynx (hypopharynx) extends from the epiglottis to the lower border of the cricoid cartilage and includes the piriform recesses on either side of the laryngeal inlet, where foreign bodies commonly lodge.

The larynx connects the pharynx to the trachea and serves both phonation and airway protection. Its skeleton consists of cartilages: the thyroid cartilage (the largest, forming the laryngeal prominence), the cricoid cartilage (the only complete cartilaginous ring of the airway, at the C6 level), and the paired arytenoid cartilages, which control vocal fold tension. The epiglottis folds over the laryngeal inlet during swallowing to prevent aspiration.

The cricothyroid membrane stretches between the thyroid and cricoid cartilages and is the preferred site for emergency surgical airway access (cricothyrotomy) because it is superficial, avascular in its midline, and rapidly accessible. The true vocal folds (vocal cords) lie within the larynx; the space between them is the glottis, and the narrowest part of the adult airway is at this level.