The upper airway consists of the pharynx and the nasal cavities; however, some authors include the larynx and trachea as well. The pharynx is can be divided into the nasopharynx, oropharynx, and laryngopharynx.
The nose is composed of bone and cartilage, which are in turn attached to the facial skeleton. It is a pyramidal structure that is divided by a midline septum into two nasal cavities. The nasal cavities are lined with mucosa that can function to heat and humidify inspired gas. The paranasal sinuses drain into the nasal cavity. The posterior portion of the mouth opens into the oropharynx. When a patient is supine and unconscious, the tongue and lower jaw may slide posteriorly leading to airway obstruction within the oropharynx.
The pharynx is a U-shaped fibromuscular tube that extends from the base of the skull to the cricoid cartilage. It is bounded anteriorly and superiorly by the nasal cavity, followed more inferiorly by the mouth, and then the larynx. These borders divide the pharynx into the nasopharynx, oropharynx, and laryngopharynx, respectively.
The epiglottis guards the opening to the glottis or the glottic inlet. It is a flap of elastic cartilage covered by mucosa that is attached superiorly and anteriorly to the larynx.
Beyond the glottic inlet is the larynx. The larynx is bounded by the aryepiglottic folds, the tip of the epiglottis, and the posterior commissure of the lower border of the cricoid cartilage. It bulges posteriorly into the laryngopharynx. Beyond the cricoid cartilage lies the trachea, which is formed by a set of U-shaped cartilaginous rings that extend to the carina before bifurcating into each mainstem bronchi.