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The Eustachian tube (or auditory tube) is a tube that links the pharynx
Pharynx

FunctionsThe pharynx is part of the digestive system and respiratory system of many organisms.Because both food and Earth's atmosphere pass through the pharynx, a flap of connective tissue called the epiglottis closes over the trachea when food is swallowed to prevent choking or Pulmonary aspiration....
 to the middle ear
Middle ear

The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear....
. In adults the Eustachian tube is approximately 35 mm long. It is named after the sixteenth century anatomist Eustachius
Bartolomeo Eustachi

Bartolomeo Eustachi , also known by his Latin name of Eustachius, was one of the founders of the science of human anatomy....
. Some modern medical books call this the pharyngotympanic tube.

Eustachian tube extends from the anterior wall of the middle ear to the lateral wall of the nasopharynx
Nasopharynx

The nasopharynx is the uppermost part of the pharynx. It extends from the base of the skull to the upper surface of the soft palate; it differs from the Mouth and larynx parts of the pharynx in that its cavity always remains patent ....
, approximately at the level of the inferior nasal concha.






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Encyclopedia


The Eustachian tube (or auditory tube) is a tube that links the pharynx
Pharynx

FunctionsThe pharynx is part of the digestive system and respiratory system of many organisms.Because both food and Earth's atmosphere pass through the pharynx, a flap of connective tissue called the epiglottis closes over the trachea when food is swallowed to prevent choking or Pulmonary aspiration....
 to the middle ear
Middle ear

The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear....
. In adults the Eustachian tube is approximately 35 mm long. It is named after the sixteenth century anatomist Eustachius
Bartolomeo Eustachi

Bartolomeo Eustachi , also known by his Latin name of Eustachius, was one of the founders of the science of human anatomy....
. Some modern medical books call this the pharyngotympanic tube.

Location

The Eustachian tube extends from the anterior wall of the middle ear to the lateral wall of the nasopharynx
Nasopharynx

The nasopharynx is the uppermost part of the pharynx. It extends from the base of the skull to the upper surface of the soft palate; it differs from the Mouth and larynx parts of the pharynx in that its cavity always remains patent ....
, 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 and raises a tubal elevation, the torus tubarius
Torus tubarius

The base of the cartilaginous portion of the Eustachian tube lies directly under the mucous membrane of the nasal part of the pharynx, where it forms an elevation, the torus tubarius or cushion, behind the pharyngeal orifice of the tube....
, 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.

Functions


Pressure equalization


Normally the 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, an event familiar to aircraft passengers or drivers in mountainous regions. Yawning or swallowing (ear clearing
Ear clearing

Ear clearing or clearing the ears is any of various maneuvers to equalize the pressure in the middle ear with the outside pressure, by letting air enter along the Eustachian tubes, as this does not always happen automatically when the pressure in the middle ear is lower than the outside pressure....
) 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 the ability to contract just these muscles voluntarily, similar to people 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'). 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
Valsalva maneuver

The Valsalva maneuver is performed by forcibly exhaling against a closed airway. Variations of the maneuver can be used either in medicine, as a test of cardiac function and autonomic nervous system of the heart or to "clear" the ears and Aerosinusitis when ambient pressure changes, as in diving or aviation....


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
Pseudoephedrine

Pseudoephedrine is a sympathomimetic amine amine commonly used as a decongestant. The salts pseudoephedrine hydrochloride and pseudoephedrine sulfate are found in many Over-the-counter drug preparations either as single-ingredient preparations, or more commonly in combination with antihistamines, paracetamol and/or ibuprofen....
. 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.

Embryologic development

The Eustachian tube is derived from the first pharyngeal pouch, which during embryogenesis
Embryogenesis

Embryogenesis is the process by which the embryo is formed and develops. It starts with the fertilization of the ovum, egg, which, after fertilization, is then called a zygote....
 forms a recess called the tympanic membrane. The distal part of the tubotympanic sulcus gives rise to the tympanic cavity
Tympanic cavity

The tympanic cavity is a small cavity surrounding the ossicles of the middle ear.It is formed from the tubotympanic sulcus, an expansion of the first branchial pouch....
, while the proximal tubular structure becomes the Eustachian tube.

Muscles

There are four muscles associated with the function of the Eustachian tube:
  • levator veli palatini
    Levator veli palatini

    The levator veli palatini is the elevator muscle of the velum palatinum in the human body. During swallowing, it contracts, elevating the soft palate to help prevent food from entering the nasopharynx....
     (innervated by the vagus nerve
    Vagus nerve

    The vagus nerve is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem and extends, through the jugular foramen, down below the head , to the neck, chest and abdomen, where it contributes to the innervation of the viscera....
    )
  • salpingopharyngeus (innervated by the vagus nerve)
  • tensor tympani
    Tensor tympani

    The tensor tympani, the larger of the two muscles of the tympanic cavity, is contained in the bony canal above the osseous portion of the auditory tube, from which it is separated by the septum canalis musculotubarii....
     (innervated by the mandibular nerve
    Mandibular nerve

    The mandibular nerve is the largest of the three branches of the trigeminal nerve....
     of CN V)
  • tensor veli palatini (innervated by the mandibular nerve of CN V)


Disorders of the Eustachian tube


Otitis media
Otitis media

Otitis media is inflammation of the middle ear, or middle ear infection .Otitis media occurs in the area between the ear drum and the inner ear, including a duct known as the Eustachian tube....
, or inflammation
Inflammation

Inflammation is the complex biological response of Blood vessel tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. It is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue....
 of the middle ear
Middle ear

The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner 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
Barotrauma

Barotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding gas or liquid....
, 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
Scuba diving

SCUBA diving is Underwater diving, or taking part in another activity, while using a scuba set. By carrying a source of breathing gas , the scuba diver is able to stay underwater longer than with the simple breath-holding techniques used in snorkeling and free-diving, and is not hindered by air lines to a remote air source....
, or a sudden decompression of an aircraft at high altitude.

Some people are born with a dysfunctional Eustachian tube, 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). 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
Otitis media

Otitis media is inflammation of the middle ear, or middle ear infection .Otitis media occurs in the area between the ear drum and the inner ear, including a duct known as the Eustachian tube....
, and may result in the mucus becoming very thick and glue-like, a condition known as glue ear.

A patulous Eustachian tube
Patulous Eustachian tube

Patulous Eustachian tube, also known as patent Eustachian tube, is the name of a rare physical disorder where the Eustachian tube, which is normally closed, instead stays intermittently open....
 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.

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.

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