True about Eustachian tube: (PGI Nov 2010)
Ans: B (Higher elastin content in adults) (Ref: Dhingra 5th/65,4th /56,12-13; The Developing Humans:Kleith8th/431-34: Longman's embryology 10th/317-23]"Eustachian 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"- Gray's 40th/626Eustachian 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 adult)36mm (31-38 mm)DirectionMore 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 1/3 of the total length of the tube and is relatively wider.Bony part 1/3; cartilaginous part 2/3TubalCartilaginous 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 cartilageOstmann's pad of fatLess in volumeLarge and helps to keep the tube closed
Length is 36mm in adults and 1.6mm to 3 mm in children
Higher elastin content in adults
Ventilatory function of ear better developed in infants
More horizontal in adults