Eustachian Tube - Anatomy, Physiology & Embryology

👂 Eustachian Tube - Anatomy, Physiology & Embryology

📝 Definition of the Eustachian Tube

The eustachian tube is a mucus lined osteocartilaginous tube connecting the lateral wall of the nasopharynx with the anterior wall of the tympanic cavity.

Named after Bartolemeus Eustachia.

What are the other names of Eustachian tube?

📏 Length & Direction

Length

👉 36 mm in adults

⭐ The anatomy of the eustachian tube in infants differs considerably from that in adults.

What are the differences between Infant and Adult Eustachian tube?

Direction

From the anterior wall of the tympanic cavity, the tube runs downwards, forwards and medially towards the nasopharynx.

👉 It forms an angle of 45 degrees with the horizontal in adults.

🚪 Openings of the Eustachian Tube

1- Tympanic Opening

• Bony in nature
• Measures about 5 x 2 mm
• Situated in the anterior wall of the middle ear, a little above the level of the floor

2- Pharyngeal Opening

• Cartilaginous in nature
• Appears as a slit like structure on endoscopy
• Situated in the lateral wall of the nasopharynx, about 1.5 cm behind the posterior end of the inferior turbinate

Which is the widest part of the Eustachian tube?

Which is the narrowest part of the Eustachian tube?

What is Torus Tubarius?

📋 Parts of the Eustachian Tube

⭐ The junction of the two parts is the isthmus.

What are the relations of the Bony Part of the Eustachian Tube?

What is the type of cartilage present in Eustachian tube?

What is the Elastin Hinge? What is its function?

Ostmann's Pad of Fat

A mass of fatty tissue related laterally to the membranous (fibrous) part of the lateral lamina.

What are the functions of Ostmann's Pad of Fat?

What are the relations of the Fibrocartilaginous Part of the Eustachian Tube?

What is the Course of the Fibrocartilaginous Part of the Eustachian Tube?

💪 Muscles Related to the Eustachian Tube

1- Tensor Veli Palatini

⭐ The only muscle that directly dilates the eustachian tube.

• Its medial fibres are attached to the lateral lamina of the tube
• On contraction, it pulls the lateral lamina, opening the tube

2- Levator Veli Palatini

• Runs inferior and parallel to the cartilaginous part of the tube
• Forms a bulk under the medial lamina
• On contraction, pushes the tube upward and medially, assisting in opening the tube

3- Salpingopharyngeus

What is the type of epithelium in the mucosal lining of the Eustachian Tube? What other cells are seen in the Eustachian tube?

🩸 Blood Supply of the Eustachian Tube

Arterial Supply

• Middle meningeal artery
• Artery of the pterygoid canal
• Ascending pharyngeal branch of the external carotid artery

Venous Drainage

• Pterygoid venous plexus
• Pharyngeal venous plexus

Lymphatic Drainage

• Retropharyngeal nodes
• Upper deep cervical nodes

🧠 Nerve Supply of the Eustachian Tube

Sensory Supply

Which nerve forms the Tympanic plexus?

Motor Supply

What is the Pharyngeal plexus made of?

⚙️ Functions of the Eustachian Tube

1️⃣ Ventilation and regulation of middle ear pressure

The eustachian tube maintains equilibrium of air pressure on either side of the tympanic membrane, keeping middle ear pressure at the ambient pressure.

What are the Factors Affecting Tubal Opening?

When does the Eustachian tube open?

Why are ear problems more common in young children?

2️⃣ Protective function

• Protection Against High Sound Pressure

• Protection Against Reflux of Nasopharyngeal Secretions

3️⃣ Drainage of middle ear secretions

The pseudostratified ciliated columnar epithelium, with cilia beating towards the nasopharynx, clears secretions and debris from the middle ear into the nasopharynx.

Using the physiology of Eustachian tube, can you explain what changes happen during ascent in an Aeroplane?

Using the physiology of Eustachian tube, can you explain what changes happen during rapid descent in an Aeroplane?

🧬 Embryology of the Eustachian Tube

The eustachian tube develops from the medial tubular part of the tubotympanic recess.

⭐ The tubotympanic recess is formed by fusion of the dorsal parts of the first and second pharyngeal pouches.

What are the structures formed from the lateral part of the tubotympanic recess?

🧠 Viva Pearls

• Length of the eustachian tube in adults is 36 mm.
• It forms an angle of 45 degrees with the horizontal in adults.
• The tympanic opening is bony and the pharyngeal opening is cartilaginous.
• The pharyngeal opening lies 1.5 cm behind the posterior end of the inferior turbinate.
• The bony part forms one-third (12 mm) and the fibrocartilaginous part two-thirds (24 mm) of the tube.
• Tensor veli palatini is the dilator of the eustachian tube.
• Levator veli palatini pushes the tube upward and medially, assisting in its opening.
• Sensory supply of both parts is ultimately by the glossopharyngeal nerve.
• Tensor veli palatini is supplied by the mandibular nerve.
• The three functions are ventilation, protection and drainage.
• The tube develops from the medial tubular part of the tubotympanic recess.

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