Eustachian tube
Encyclopedia
The Eustachian tube is a tube that links 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 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...

 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. The hollow space of the middle ear has...

. It is a part of the middle ear. In adult humans the Eustachian tube is approximately 35 mm long. It is named after the sixteenth-century anatomist Bartolomeo Eustachi
Bartolomeo Eustachi
Bartolomeo 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.

Anatomy

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 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
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

 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, the torus of the auditory tube, 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
Hyrax
A hyrax is any of four species of fairly small, thickset, herbivorous mammals in the order Hyracoidea. The rock hyrax Procavia capensis, the yellow-spotted rock hyrax Heterohyrax brucei, the western tree hyrax Dendrohyrax dorsalis, and the southern tree hyrax, Dendrohyrax arboreus live in Africa...

, an evagination of the eustachian tube is known as the guttural pouch
Guttural pouch
In the equids and some rodent-like species such as the desert hyrax, the guttural pouch is a pair of air chambers in the neck just behind the skull and below the ears...

 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.

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, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...

 forms the tubotympanic recess. The distal part of the tubotympanic sulcus gives rise to the tympanic cavity
Tympanic cavity
The tympanic cavity is a small cavity surrounding the bones of the middle ear.It is formed from the tubotympanic recess, 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
    Levator veli palatini
    The levator veli palatini is the elevator muscle of the soft palate 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 , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...

    )
  • 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...

     (innervated by the mandibular nerve
    Mandibular nerve
    The 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)

Pressure equalization

Under normal circumstances, the human Eustachian tube is closed, but it can open to let a small amount of air through to prevent damage by equalizing pressure between the middle ear and the atmosphere. Pressure differences cause temporary conductive hearing loss
Conductive hearing loss
Conductive hearing loss occurs when there is a problem conducting sound waves anywhere along the route through the outer ear, tympanic membrane , or middle ear ....

 by decreased motion of the tympanic membrane and ossicles
Ossicles
The ossicles are the three smallest bones in the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth . The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss...

 of the ear. Various methods of 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...

 such as yawning, swallowing, chewing gum, or performing the valsalva maneuver
Valsalva maneuver
The Valsalva maneuver or Valsalva manoeuvre is performed by moderately forceful attempted exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut...

 may be used intentionally to open the tube and equalize pressures. When this happens, humans hear a small popping sound, an event familiar to aircraft passengers, scuba divers, or drivers in mountainous regions.

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 drug of the phenethylamine and amphetamine chemical classes. It is used as a nasal/sinus decongestant and stimulant, or as a wakefulness-promoting agent....

. Earaches are more common in children because the tube is more horizontal and shorter, and has a smaller floppier opening, making the movement of fluid more difficult.

Disorders

Otitis media
Otitis media
Otitis media is inflammation of the middle ear, or a middle ear infection.It occurs in the area between the tympanic membrane 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 inflammation
Inflammation
Inflammation is part of 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 and to initiate the healing process...

 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. 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 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 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 diving
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....

, 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 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. 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 a middle ear infection in some cases.

Eustachian tube dysfunction can be caused by recurring and chronic cases of sinus infection
Sinusitis
Sinusitis is inflammation of the paranasal sinuses, which may be due to infection, allergy, or autoimmune issues. Most cases are due to a viral infection and resolve over the course of 10 days...

. This results from excessive mucus production which causes obstruction to the openings of the Eustachian tubes.

External links




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