<prompt> True about Eustachian tube: PGI Nov 2010Length is 36mm in adults and 1.6mm to 3 mm in childrenHigher elastin content in adultsVentilatory function of ear better developed in infantsMore horizontal in adults  <response>: Ans: B Higher elastin content in adults Ref: Dhingra 5th65,4th 56,12-13; The Developing Humans:Kleith8th431-34: Longmans embryology 10th317-23Eustachian tube serves to ventilate the middle ear exchange nasopharyngeal air with air in the middle ear. In children, ET is relatively narrow. It is prone to obstruction when mucosa swell in response to infection or allergic challenge it results in middle ear effusion- Grays 40th626Eustachian TubeIt connects nasopharynx with the tympanic cavity. In adults it is about 36 cm long runs downwards, forwards medially from its tympanic end, forming an angle of 45 with the horizontal.The tympanic end of the tube is body is situated in the anterior wall of the middle ear. A little above the level of the floor. The pharyngeal end of the tube is slit-like situated in the lateral wall of the nasopharynx, 1- 1.25 cm behind the posterior end of inferior turbinate. It develops from the first arch partly from the second arch -Dhingra 5th 14Table Dhingra 5th,65: Differences Between Infant and Adult Eustachian tube InfantAdultLength13-18mm birth about half as long as in adult36mm 31-38 mmDirectionMore horizontal.At birth, it forms an angle of 100 with the horizontal At age 7 and later it is 45degForms an angle of 45Qwith the horizontalAngulation at isthmusNo angulationAngulation presentBony versus cartilaginousBony parts is slightly longer than 13 of the total length of the tube and is relatively wider.Bony part 13; cartilaginous part 23TubalCartilaginous partFlaccid. Retrograde reflux of nasopharyngeal secretions can occurComparatively rigid, Remains closed and protects the middle ear from the refluxThe density of elastin at the hingeLess dense; tube does not efficiently close by recoilDensity of elastin moreand helps to keep the tube closed by the recoil of cartilageOstmanns pad of fatLess in volumeLarge and helps to keep the tube closed 