Growth and Development of Human Laryngeal Functions.

OBJECTIVES

Human laryngeal functions are respiration (airway), local immunity, airway protection (swallowing) and phonation. Newborn larynges resemble those of non-human primates and lack mature functional structures like adults. This study summarizes the development of laryngeal functions, focusing particularly on their morphological and functional interrelationships.

METHODS

Human larynges from autopsy cases were examined using whole-organ serial section studies, integrating findings from our previous studies.

RESULTS

In newborns, the posterior glottis (intercartilaginous portion) occupied most of the glottis and was covered with respiratory epithelium. Neither a vocal ligament nor an adult-like layered structure of the vocal fold was present. Consequently, the newborn glottis appeared to be favored for respiration over phonation. Serous laryngeal glands supporting local immunity were well developed at supraglottis. Because the larynx had not yet descended, two-tube configuration of supralaryngeal vocal tract was absent. During the first 9 years of life, laryngeal descent enabled vocal tract formation. The preepiglottic space, initially a small area just anterior to the epiglottis at birth, expanded astride the epiglottis as the vocal tract developed, enhancing epiglottic retroflection and reducing aspiration risk. By the end of adolescence, the vocal ligament and layered structure of the vocal fold matured, and the glottis acquired adult phonatory morphology. Therefore, the human glottis acquired the dimensions and morphological characteristics for phonation as adults.

CONCLUSIONS

Laryngeal functions develop in a hierarchical sequence: respiration (airway) and local immunity first, followed by airway protection (swallowing) and finally phonation. Humans progressively acquire these functions in parallel with structural maturation of the larynx.