Definition of Eustachian tube

Eustachian tube: The tube that runs from the middle ear to the pharynx. The function of the Eustachian tube is to protect, aerate and drain the middle ear (and mastoid). Occlusion of the Eustachian tube leads to the development of middle ear inflammation (otitis media). The Eustachian tube is also called the otopharyngeal tube (because it connects the ear to the pharynx) and the auditory tube (and in Latin, the tuba acustica, tuba auditiva, and tuba auditoria).

The pharynx is subdivided into 3 parts: the upper part called the nasopharynx, the middle part called the oropharynx, and the lower part called the hypopharynx. The Eustachian tube opens into the nasopharynx.

The Eustachian tube measures only 17-18mm and is horizontal at birth. As it grows to double that length, it grows to be at an incline of 45 degrees in adulthood so that the nasopharyngeal orifice (opening) in the adult is significantly below the tympanic orifice (the opening in the middle ear near the ear drum).

The shorter length and the horizontality of the Eustachian tube in infancy protects the middle ear poorly, makes for poor drainage of fluid from the middle ear, and predisposes infants and young children to middle ear infection. The greater length and particularly the slope of the tube as it grows serves more effectively to protect, aerate and drain the middle ear.

The Eustachian tube in the adult is opened by two muscles (the tensor palati and the levator palati) but the anatomy of children permits only one of these muscles (the tensor palati) to work. This is a particular problem for children born with cleft palate who have poor function of that muscle; they suffer from Eustachian tube and middle ear problems until the second muscle (the levator palati) begins to function.

The tube serves to adjust the pressure of the air within the middle ear to that of ambient air. It is harder to get air into the middle ear than get it out, which is why we have more trouble with our ears when a plane is descending than when it takes off.

The tube bears the name of Bartolomeo Eustachi, a 16th-century (c. 1500-1510 to 1574) Italian physician. In 1562 and 1563 he produced a remarkable series of treatises on the kidney, the teeth, and the ear. These were published in Opuscula anatomica (1564). The treatise on the kidney was the first work specifically dedicated to that organ. He was the first to study the teeth in any detail. The treatise on the ear, the auditory organ (De auditus organis), provided a correct account of the auditory tube that is still referred to by his name. In 1552 Eustachi prepared a series of 47 anatomical plates, which (although they were published long after his death) alone assured him a distinguished position in the history of anatomy. He placed anatomy in the service of medicine. With Vesalius and Fallopio (of Fallopian tube fame), Eustachi is often seen as one of the three heroes of human anatomy. (Historical information based on the Catalog of the Scientific Community of the 16th and 17th Centuries by Richard S Westfall for the Galileo Project.)

Common Misspellings: eustacian tube