Auditory Tube

An auditory tube (eustachian tube) connects each middle ear to the throat. This tube allows air to pass between the tympanic cavity and the outside of the body by way of the throat (nasopharynx) and mouth. It helps maintain equal air pressure on both sides of the eardrum, which is necessary for normal hearing (see fig. 12.11).

The function of the auditory tube becomes noticeable during rapid change in altitude. As a person moves from a high altitude to a lower one, the air pressure on the outside of the tympanic membrane steadily increases. As a result, the tympanic membrane may be pushed inward, out of its normal position, impairing hearing.

When the air pressure difference is great enough, some air may force its way up through the auditory tube into the middle ear. This equalizes the pressure on both sides of the tympanic membrane, which moves back into its regular position, causing a popping sound as normal hearing returns. A reverse movement of air ordinarily occurs when a person moves from a low altitude to a higher one.

The auditory tube is usually closed by valvelike flaps in the throat, which may inhibit air movements into the middle ear. Swallowing, yawning, or chewing aid in opening the valves and can hasten equalization of air pressure.

Signs of an ear infection in an infant or toddler are hard to miss — irritability, screaming incessantly for no apparent reason, perhaps fever or tugging on the affected ear. A doctor viewing the painful ear with an instrument called an otoscope sees a red and bulging eardrum. The diagnosis: otitis media, or a middle ear infection.

Ear infections occur because the mucous membranes that line the auditory tubes are continuous with the linings of the middle ears, creating a conduit for bacteria infecting the throat or nasal passages to travel to the ear. This route to infection is greater in young children because their auditory tubes are shorter than they are in adults. Half of all children in the United States have an ear infection by the first birthday, and 90% have one by age six.

Physicians treat acute otitis media with antibiotics. Because recurrent infections may cause hearing loss and interfere with learning, children with recurrent otitis media are often fitted with tympanostomy tubes, which are inserted into affected ears during a brief surgical procedure. The tubes form a small tunnel through the tympanic membrane so the ears can drain. By the time the tubes fall out, the child has usually outgrown the susceptibility to ear infections.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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