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. The Eustachian tube permits the gas pressure in the middle ear cavity to adjust to external air pressure. When you are descending in an airplane, the Eustachian tube opens when your ears 'pop.' 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. Occlusion of the Eustachian tube can lead to the development of middle ear infection (otitis media). The Eustachian tube opens into the nasopharynx. The Eustachian tube measures only 17 to 18 mm, and it is horizontal at birth. As it grows to double that length, it grows
to be positioned at an incline of 45 degrees in
adulthood. For this reason the nasopharyngeal opening in an adult is significantly below the tympanic opening, found in the middle ear near the eardrum. The shorter length and the horizontal orientation 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 serve 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 the tensor palati to work. Also known as otopharyngeal tube because it connects the ear to the pharynx and auditory tube.
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