--- title: "Eustachian Tube - Anatomy, Physiology & Embryology" description: "ENT notes on Eustachian Tube - Anatomy, Physiology & Embryology." source: "The ENT Resident" author: "Dr. Mausumi Das" canonical_url: "https://www.theentresident.com/ent-notes-lectures/eustachian-tube-anatomy-physiology-embryology" categories: ["Otology"] video: "https://www.youtube.com/watch?v=ldRR29FyE_4" image: "https://media.theentresident.com/og-images/eustachian-tube-anatomy-physiology-embryology.png" --- # Eustachian Tube - Anatomy, Physiology & Embryology ENT notes on Eustachian Tube - Anatomy, Physiology & Embryology. Watch the full video lecture on YouTube: https://www.youtube.com/watch?v=ldRR29FyE_4 ## 👂 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 | Part | Proportion | Length | | --- | --- | --- | | **Bony part** | One-third | 12 mm | | **Fibrocartilaginous part** | Two-thirds | 24 mm | ⭐ 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 | Part | Nerve Supply | | --- | --- | | Pharyngeal (cartilaginous) part | Pharyngeal branch of the glossopharyngeal nerve, via the **pharyngeal plexus** | | Tympanic (bony) part | **Tympanic plexus** | > Which nerve forms the Tympanic plexus? #### Motor Supply | Muscle | Nerve Supply | | --- | --- | | Tensor veli palatini | Mandibular branch of the trigeminal nerve | | Levator veli palatini | Pharyngeal plexus | | Salpingopharyngeus | Pharyngeal plexus | > 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. --- ## About This Note This free ENT note on Eustachian Tube - Anatomy, Physiology & Embryology was written by Dr. Mausumi Das and is paired with a corresponding video lecture. 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