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Eustachian tube
	Anatomy of the human ear.
	Malleus Tensor Tympani Incus Stapedius Labyrinth Stapes Auditory Canal Tympanic Membrane; (Ear Drum) Eustachian Tube Tympanic cavity
	The middle ear
Latin	tuba auditiva; tuba auditoria; tuba auditivea
Gray's	subject #230 1042
Precursor	first branchial pouch
MeSH	Eustachian+tube

The Eustachian tube (or auditory tube or pharyngotympanic tube) is a tube that links the pharynx to the middle ear. In adults the Eustachian tube is approximately 35 mm long. It is named after the sixteenth century anatomist Eustachius.^[1] Some modern medical books call this the pharyngotympanic tube.^[2]

[edit] Location

The Eustachian tube extends from the anterior wall of the middle ear to the lateral wall of the nasopharynx, approximately at the level of the inferior nasal concha. A portion of the tube (~1/3) proximal to the middle ear is made of bone; the rest is composed of cartilage^[3] and raises a tubal elevation, the torus tubarius, in the nasopharynx where it opens.

In the equids (horses) and some rodent-like species such as the desert hyrax, an evagination of the eustachian tube is known as the guttural pouch and is divided into medial and lateral compartments by the stylohyoid bone of the hyoid apparatus. This is of great importance in equine medicine as the pouches are prone to infections, and due to their intimate relationship to the cranial nerves (VII, IX, X, XI) and the internal and external carotid artery, various syndromes may arise relating to which is damaged. Epistaxis (nosebleed) is a very common presentation to veterinary surgeons and this may often be fatal unless a balloon catheter can be placed in time to suppress bleeding.

[edit] Functions

[edit] Pressure equalization

Normally the human Eustachian tube is closed, but it can open to let a small amount of air through to equalize the pressure between the middle ear and the atmosphere. When this happens we hear a small pop or squeezie sound, an event familiar to aircraft passengers or drivers in mountainous regions. Yawning or swallowing (ear clearing) can pull on muscles in the neck, causing the tube to open. Without this airway, air would be unable to escape from one's ear, the middle ear would be isolated from the atmosphere, and could be easily damaged by pressure changes.

Some people are born with an ability to voluntarily contract just these muscles called Voluntary Tubal Opening, similar to the ability of those who can wiggle their ears. Those who have this ability can hear "pop" or "click" sound in the middle ear when actuating these muscles, and are able to hold the muscle contraction (some refer to this as 'clicking your ears to equalize the pressure').^{[citation needed]} Doing so will make one's voice sound louder to oneself. This ability allows such people to voluntarily equalize pressures at will when making rapid ascents or descents, typically in aircraft flights or large elevation changes in either tall buildings or mountainous treks. When the breath (inhale or exhale) is controlled, air pressure can be intentionally increased or decreased in the middle ear (breathing through the nose only or mouth), where the feeling of a cool air breeze can be felt inside the eustachian tube.

Occasionally, if the voluntary contraction timing is missed during a rapid pressure change, a slight yawning (opening of the jaw) action combines to assist in pressure equalization.

See also: Valsalva maneuver

[edit] Mucus drainage

The Eustachian tube also drains mucus from the middle ear. Upper airway infections or allergies can cause the Eustachian tube to become swollen, trapping bacteria and causing ear infections. This swelling can be reduced through the use of pseudoephedrine. Earaches are more common in children because the tube is more horizontal, shorter and has a smaller floppier opening, making the movement of fluid more difficult.

[edit] Embryologic development

The Eustachian tube is derived from the first pharyngeal pouch, which during embryogenesis forms a recess called the tympanic membrane. The distal part of the tubotympanic sulcus gives rise to the tympanic cavity, while the proximal tubular structure becomes the Eustachian tube.

[edit] Muscles

There are four muscles associated with the function of the Eustachian tube:

Levator veli palatini (innervated by the vagus nerve)
Salpingopharyngeus (innervated by the vagus nerve)
Tensor tympani (innervated by the mandibular nerve of CN V)
Tensor veli palatini (innervated by the mandibular nerve of CN V)

[edit] Disorders

Otitis media, or inflammation of the middle ear, commonly affects the Eustachian tube. Children under 7 are more susceptible to this condition because the Eustachian tube is shorter and at more of a horizontal angle than in the adult ear.

Barotitis, a form of barotrauma, may occur when there is a substantial difference in air or water pressure between the outer inner and the inner ear, for example in a rapid ascent while scuba diving, or a sudden decompression of an aircraft at high altitude.

Some people are born with a dysfunctional Eustachian tube,^[4] which is much slimmer than the usual human Eustachian tube. This may be genetic, but it has also been suggested to be a condition in which the patient did not fully recover from the effects of pressure on the middle ear during birth (retained birth compression).^[5] This disorder may result in a large amount of mucus accumulating in the middle ear, often impairing hearing to a degree. This condition is known as otitis media with effusion, and may result in the mucus becoming very thick and glue-like, a condition known as glue ear.

A patulous Eustachian tube is a rare condition, in which the Eustachian tube remains intermittently open, causing an echoing sound of the person's own heartbeat, breathing, and speech. This may be temporarily relieved by moving into a position where the head is upside down.

Smoking can also cause damage to the cilia that protect the Eustachian tube from mucus, which can result in the clogging of the tube and a buildup of bacteria in the ear, leading to an inner ear infection in some cases.^[6]

Eustachian tube dysfunction can be caused by recurring and chronic cases of sinus infection. This results from excessive mucus production which causes obstruction to the openings of the Eustachian tubes.