Functional anatomy of the Eustachian tube.

The Eustachian tube (ET) is divided in 3 portions: a bony portion, a cartilaginous portion, and a junctional portion. From an anatomical-functional point of view, the bony portion of ET is the region of ventilation and clearance of secretions, and is lined by pseudostratified, ciliated, columnar epithelium, with an anti-gravitational direction of the drainage. The ET in the bony portion is in a state of forced opening. The cartilaginous portion is instead the heart of this dynamic system tube, because the mechanism of opening and closing of the tube is at this level. ET is normally closed, and it opens only during swallowing, being essential for good functioning of the middle ear, because it provides ventilation from the nasopharynx to the middle ear, and, at the same time, clearance of secretions from the middle ear-mastoid unit to the nasopharynx. Moreover, the ET protects the middle ear against nasopharyngeal pressure variations, ascending secretions, and microorganisms. The ability to develop all these functions makes the tube a complex organ.