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eustachian tube

 
Dictionary: eu·sta·chian tube or Eu·sta·chian tube (yū-stā'shən, -shē-ən, -kē-ən) pronunciation

n. Anatomy
A slender tube that connects the tympanic cavity with the nasal part of the pharynx and serves to equalize air pressure on either side of the eardrum.

[After Bartolomeo EUSTACHIO.]


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World of the Body:

eustachian tube

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Lying beyond the eardrum is the middle ear, a tiny air-filled cavity in the temporal bone of the skull, which is connected to the back of the throat by the eustachian tube. In adult humans, the eustachian tube, which was first described by Bartholomeo Eustachio in the sixteenth century, is just less than 4 cm long and lies at an angle of 45° relative to the horizontal plane. The bottom end of the eustachian tube, which opens into the nasopharynx, is composed of membrane and cartilage and is normally closed. However, it is essential for proper sound conduction through the ear that the eustachian tube opens periodically, so that the air pressure within each middle ear can be matched to that of the surrounding atmosphere. This occurs as a result of the contraction of the muscles that surround the eustachian tube during sneezing, forceful nose blowing, yawning, and swallowing (both when eating or drinking and throughout the day and night as build up of saliva and mucus stimulates the swallowing reflex). Opening of the eustachian tube also serves to drain any fluid that builds up in the middle ear into the nasopharynx.

The discomfort in the ears that sometimes follows marked changes in atmospheric pressure — caused, for example, by rapid descent in an aircraft or compression in a diving suit — is due to differences in pressure on either side of the eardrum. The unpleasant feeling can usually be overcome by yawning or some other means of opening the eustachian tubes. This is why scuba divers are taught to hold their noses and blow as they descend, and the same technique helps when an aircraft is landing.

The middle ear cavity, eustachian tube, and upper respiratory tract are lined by a continuous layer of mucous membrane. It is therefore not surprising that infections of the nasopharynx — including the common cold — readily reach the middle ear via the eustachian tube. Infants and young children are particularly susceptible to such acute infections, which usually cause ear pain and fever, possibly because the eustachian tube is wider, shorter, and more horizontal than it is in adults. This can lead to a build up of fluid in the middle ear in a condition known as otitis media with effusion or ‘glue ear’.

Accumulation of mucus in the eustachian tube, associated with inflammation of the middle ear, impedes the flow of air along the tube and results in negative pressure within the middle ear cavity. This causes the eardrum to be pushed inwards by the greater pressure of the atmosphere. Occlusion of the eustachian tube produces a sense of fullness in the affected ear and a mild conductive hearing loss, which may be increased if there is fluid in the middle ear. The sensation of popping in the ears that results when the nose is blown vigorously during a cold is due to air being forced up a blocked eustachian tube. Because of the increased difficulty in equalizing middle ear pressure, people with upper respiratory tract infections are more likely to suffer from ear discomfort when flying.

— Andrew J. King

Bibliography

  • Bluestone, C. D. and Klein, J. O. (1995). Otitis media in infants and children, (2nd edn). W. B. Saunders, Philadelphia

See also diving; flying; hearing; swallowing.

Dental Dictionary:

eustachian tube

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n

A tube, lined with mucous membrane, that joins the nasopharynx and the middle ear cavity, allowing equalization of the air pressure in the middle ear with atmospheric pressure. Also called the auditory tube.

Sports Science and Medicine:

Eustachian tube

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The tube, sometimes called the auditory canal, which connects the middle ear to the pharynx. It allows pressure to be equalized on either side of the eardrum.

 
Columbia Encyclopedia:

Eustachian tube

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Eustachian tube (yūstā'shən) [for Bartolomeo Eustachi], a hollow structure of bone and cartilage extending from the middle ear to the rear of the throat, or pharynx, technically known as the pharyngotympanic or auditory tube. By permitting air to leave or enter the middle ear, the tube equalizes air pressure on either side of the eardrum. The tube can become blocked, as by enlarged adenoids or the mucous secretions of a cold, so that external and internal pressure become imbalanced. Earache and diminution of hearing may result. The tube may also serve as a pathway to the ear for infections of the throat. A common ear disease known as Otitis Media, usually appearing in early childhood, is thought to be related to the Eustachian tube. The tube tends to be shorter and more horizontal among children, factors which facilitate the spread of infections from upper respiratory diseases to the middle ear, as well as the accumulation of fluids in the region.


Health Dictionary:

Eustachian tube

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(yooh-stay-shuhn, yooh-stay-kee-uhn)

A tube made up of bone and cartilage that connects the middle ear to the back of the mouth.

  • Swallowing during airplane takeoffs and landings allows air to move through the Eustachian tube to equalize pressure across the eardrum, causing the ears to “pop.”

  • Aviation Dictionary:

    eustachian tube

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    The tube connecting the middle ear to the breathing passage. A person suffers from an earache if this tube is blocked and the aircraft is descending. The tube opens automatically and equalizes the pressure across the middle ear while climbing. It also opens during descent when a person swallows, yawns, or carries out the Valsalva maneuver. The eardrum can be perforated or damaged if the eustachian tube is blocked (as in congestion) and the aircraft descends rapidly. This is caused by the very high differential pressure inside the ear and the atmosphere. See also Valsava maneuver.

    Aviation Dictionary


    The Eustachian tube is normal in the case on the left. In the case on the right, it is blocked. The subject is likely to suffer from pain and injury in case he/she flies with sinus congestion resulting in the eustachian tube getting blocked.


    Wikipedia:

    Eustachian tube

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    Eustachian tube
    Ear-anatomy-text-small-en.svg
    Anatomy of the human ear.
    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]

    Contents

    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.

    Functions

    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 can teach themselves to voluntarily contract just these muscles called voluntary tubal opening. 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

    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.

    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.

    Muscles

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

    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]

    Adenoids in children can lead to the misleading impression that said children are 'dull' due to the fact that the swollen lymphoid tissue may block the nasopharyngeal opening of the Eustachian tube, resulting in deafness and buck teeth as the child is forced to breath through their mouth to avoid the blockage.

    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.

    Additional images

    See also

    References

    1. ^ Eustachian tube at Who Named It?
    2. ^ pharyngotympanic (auditory) tube at eMedicine Dictionary
    3. ^ Ear - Dissector Answers at University of Michigan Medical School
    4. ^ Eustachian Tube Function and Dysfunction at Baylor College of Medicine
    5. ^ "FAQs - Cranial Osteopathy". The Children's Clinic. http://www.childrensclinic.co.uk/faq_cranial_osteopathy.htm#17. Retrieved 2008-12-23. 
    6. ^ Dubin MG, Pollock HW, Ebert CS, Berg E, Buenting JE, Prazma JP (2002). "Eustachian tube dysfunction after tobacco smoke exposure". Otolaryngology - Head and Neck Surgery 126 (1): 14–19. PMID 11821759. 

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