Structure:

The pharyngotympanic tube is a narrow canal that connects the middle ear (tympanic cavity) to the nasopharynx.[1] It lies within the parapharyngeal region of the skull base, extending from the anterior wall of the tympanic cavity to the lateral wall of the nasopharynx.[1] 

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The tube measures approximately 36 mm in total length.[1] The posterolateral one-third (approximately 12 mm), adjacent to the tympanic cavity, is bony and lies within the petrous part of the temporal bone.[1] The remaining anteromedial two-thirds (approximately 24 mm) consists of elastic fibrocartilage, which opens into the nasopharynx.[1] 

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The pharyngotympanic tube is lined by respiratory mucosa that is continuous posteriorly with the mucosa of the tympanic cavity and anteriorly with the mucosa of the nasopharynx.[1] This continuity facilitates pressure regulation and mucociliary clearance between the middle ear and upper respiratory tract.[1]

Function:

The primary function of the pharyngotympanic tube is to equalize air pressure between the middle ear and the external atmosphere.[1] By intermittently opening—most commonly during swallowing, yawning, or chewing—the tube allows air to pass between the nasopharynx and the tympanic cavity.[1] 

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Pressure equalization enables the tympanic membrane to vibrate freely, maintaining optimal tension for efficient transmission of sound waves through the ossicular chain.[1,2] Dysfunction of the tube may result in impaired ventilation of the middle ear, contributing to conditions such as otitis media, barotrauma, or conductive hearing loss.[2] 

References:

1. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 6th ed. International ed. Lippincott Williams & Wilkins; 2010.

2. Szymanski A, Agarwal A. Anatomy, head and neck, ear Eustachian tube. In: StatPearls. StatPearls Publishing; 2023. https://www.ncbi.nlm.nih.gov/books/NBK482338/