The
Eustachian tube (or
auditory tube or
pharyngotympanic tube) is a tube that links the
pharynxThe pharynx is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial, or superior, to the esophagus, larynx, and trachea.-Functions:...
to the
middle earThe 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. The hollow space of the middle ear has...
. In adults the Eustachian tube is approximately 35 mm long. It is named after the sixteenth century anatomist
EustachiusBartolomeo Eustachi , also known by his Latin name of Eustachius, was one of the founders of the science of human anatomy.-Life:...
. 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
nasopharynxThe 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 oral and laryngeal parts of the pharynx in that its cavity always remains patent .-Lateral:On its lateral wall is the pharyngeal ostium of the...
, 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 tubariusThe 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
hyraxA hyrax is any of four species of fairly small, thickset, herbivorous mammals in the order Hyracoidea. They live in Africa and the Middle East....
, 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.
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 clearingEar 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 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'). 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 maneuverThe Valsalva maneuver or Valsalva manoeuvre is performed by forcible exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut...
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
pseudoephedrinePseudoephedrine is a sympathomimetic amine commonly used as a decongestant. The salts pseudoephedrine hydrochloride and pseudoephedrine sulfate are found in many over-the-counter preparations either as single-ingredient preparations, or more commonly in combination with antihistamines, paracetamol...
. 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
embryogenesisEmbryogenesis is the process by which the embryo is formed and develops. It starts with the fertilization of the ovum which, after fertilization, is referred to as a zygote. The zygote undergoes rapid mitotic divisions with no significant growth and cellular differentiation, leading to...
forms a recess called the tympanic membrane. The distal part of the tubotympanic sulcus gives rise to the
tympanic cavityThe tympanic cavity is a small cavity surrounding the bones of the middle ear.It is formed from the tubotympanic sulcus, an expansion of the first pharyngeal 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
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 nerveThe vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem...
)
- salpingopharyngeus (innervated by the vagus nerve)
- 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...
(innervated by the mandibular nerveThe mandibular nerve is the largest of the three branches of the trigeminal nerve.-Roots:It is made up of two roots:* a large sensory root proceeding from the inferior angle of the trigeminal ganglion....
of CN V)
- tensor veli palatini (innervated by the mandibular nerve of CN V)
Disorders of the Eustachian tube
Otitis mediaOtitis 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. It is one of the two categories of ear inflammation that can underlie what is commonly called an earache,...
, or
inflammationInflammation is the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue. Inflammation is not a...
of the
middle earThe 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. The hollow space of the middle ear has...
, 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
barotraumaBarotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid....
, 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 divingScuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater for recreation, commercial or industrial reasons.Unlike early diving, which relied exclusively on air pumped from the surface, scuba...
, 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, and may result in the mucus becoming very thick and glue-like, a condition known as
glue ear.
A
patulous Eustachian tubePatulous 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. When this occurs, the patient experiences autophony, the hearing of self-generated sounds...
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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