(SYN. EUSTACHIAN TUBE/AUDITORY TUBE).
It attaches the nasopharynx together with the tympanic cavity and is a mucous-lined osseocartilaginous station. On each side of the tympanic membrane for its appropriate shaking, it keeps the equilibrium of air pressure.
From its tympanic end in an adult, it’s around 36 millimeters long and runs downwards, forwards and medially.
The pharyngotympanic tube is splitted into 2 parts, viz.
- Osseous or bony part: It creates one-third (12 millimeters) of the absolute length of the tube and it is posterolateral part and It opens into the middle ear cavity and is located between the tympanic and petrous parts of the temporal bone.
- Cartilaginous part: It’s anteromedial part and creates two-third (24 millimeters) of the tube.
The 2 parts meet at isthmus that’s the narrowest part of the tube. The cartilaginous part is made from one bit of elastic fibrocartilage that is folded upon itself in this type of fashion it creates all of the medial wall, roof and a part of the lateral wall. The remainder of the lateral wall is filled up by the fibrous membrane.
The cartilaginous part is located in the groove between the petrous part of the temporal bone and the posterior border of the higher wing of the sphenoid bone.
Ends of the Tube
The tympanic end of the tube is small and bony. It’s situated in the anterior wall of the middle ear, a little above its floor.
The pharyngeal end is comparatively large and slit-like (vertically). It’s situated in the lateral wall of the pharynx, about 1.25 cm behind the posterior end of inferior nasal concha. The pharyngeal orifice is the broadest part of the tube.
Liner of the Tube
The tube is lined by pseudostratified ciliated columnar epithelium with interspersed goblet cells. The cilia beat in the course of nasopharynx and therefore help drain the secretions and fluid from the middle ear into the nasopharynx.
Pharyngotympanic Tubes of an Infant and an Adult
Differences between the eustachian tube of an infant and an adult.
Since the eustachian tube is shorter, wider and much more horizontal in babies, the infection from nasopharynx can easily get to the middle ear; for this rationale, middle ear diseases are much more common in babies and young children than in adults.
The following are the functions of the pharyngotympanic tube:
- Preserves equilibrium of air pressure on each side of tympanic membrane. At rest, the tube stays closed but during swallowing, yawning and sneezing it reflexly opens.
- Protection of middle ear by preventing the transmission of high sound pressure from nasopharynx to middle ear as normally the tube stays closed.
- Clearance of middle ear secretions by aggressive opening and closure of the tube. The cilia of mucous lining of the tube beat in the course of nasopharynx and drain the secretion of the middle ear into the nasopharynx.
- An individual consumes once every minute when alert and once every 5 minutes when sleeping.
The pharyngotympanic tube equalizes the pressure in the middle ear together with the atmospheric pressure to allow free movement of the tympanic membrane. If the tube is obstructed because of inflammation of tubal tonsil, the remaining air in the middle ear is absorbed into the blood vessels of its mucous membrane, causing a fall of pressure in it and consequent retraction of tympanic membrane. This causes disturbance of hearing and acute earache because of retraction of tympanic membrane (RTM). The persistently decreased air pressure inside the middle ear is corrected by regular introduction of air by eustachian catheter.