Development of the Respiratory Primordium

• at the fourth week of development the respiratory primordium appears as an outgrowth (laryngotracheal groove) from the ventral wall of the foregut (primitive pharynx)

• the laryngotracheal groove evaginates to form the laryngotracheal diverticulum dividing the foregut into a dorsal portion (esophagus) and ventral portion (larynx, trachea, and lung) separated by the tracheoesophageal septum

• the respiratory primordium (ventral portion) maintains open communication with the pharynx through the laryngeal orifice

• epithelial proliferation obliterates the laryngeal lumen, recanalization occurs by the tenth week (no recanalization results in stenosis)

• three tissue swellings (median swelling behind the hypobranchial eminence, which forms the epiglottis, and two lateral swellings that form the arytenoid cartilages) surround the laryngeal orifice

Branchial Arch Derivatives

II: lesser horn and upper portion of the hyoid bone

III: greater horn and lower portion of the hyoid bone

IV: supraglottic structures (thyroid cartilage), superior laryngeal nerve (SLN) structures (cricothyroid muscle and pharyngeal constrictors)

V/VI: glottic/subglottic structures (cricoid, cuneiform, corniculate, and arytenoid cartilages) and recurrent laryngeal nerve (RLN) structures (all intrinsic laryngeal muscles except the cricothyroid)

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