Pharynx & Esophagus Lecture

Pharynx (Throat)

  • Position & Connections

    • Superiorly opens to the nasal cavity

    • Anteriorly / centrally opens to oral cavity

    • Inferiorly bifurcates into:

    • Esophagus (posterior)

    • Larynx → trachea (anterior)

  • Epithelial lining

    • Moist stratified squamous epithelium (mucous membrane)

    • “Moist” = mucous-secreting; far fewer keratinized dead cells than epidermis

    • Function: protection against abrasion from food bolus

    • Same epithelium continues through the entire esophagus; switches to simple epithelium in the stomach

  • Rule of thumb

    • Wherever you see a stratified epithelium in the body, its purpose is protection

Anatomical Subdivisions (superior ➞ inferior)

  • Nasopharynx

    • Contains pharyngeal tonsils (R & L)

    • Houses openings of the auditory (Eustachian) tubes

    • Air-filled passage to the middle ear (temporal bone)

    • Equalises pressure across the tympanic membrane

    • Example: cabin pressure changes during airplane take-off/landing → muffled hearing

  • Oropharynx

    • Adjacent to oral cavity

    • Contains palatine tonsils & lingual tonsils

  • Laryngopharynx

    • Opens to both larynx and esophagus

    • Spatial note: esophagus lies posterior to larynx/trachea → digestive tract runs posterior to respiratory tract from this point downward

Functional Role

  • Acts as a common passageway for both swallowed material and inhaled/exhaled air

  • Performs no mechanical or chemical digestion

Esophagus

  • Muscular tube (~25 cm) running through thorax

  • Passes through diaphragm at the esophageal hiatus to enter stomach

Sphincters (= “muscular valves”)

  • Upper Esophageal Sphincter (UES)

    • Junction of pharynx & esophagus

    • Tightly contracted except during swallowing

  • Lower Esophageal Sphincter (LES)

    • Junction of esophagus & stomach

    • Prevents reflux of gastric contents

    • Failure ➞ esophageal reflux / heartburn; stomach contents have \text{pH}=1\text{–}2 and damage unprotected esophageal mucosa

  • General principle: Every digestive-tract junction is guarded by a sphincter

Wall Structure (generic four-layer pattern—first appears here)

  • Mucosa

    • Stratified squamous epithelium

    • Lamina propria (loose CT)

    • Muscularis mucosae (thin smooth muscle)

  • Submucosa (loose/areolar CT)

    • Blood/lymph vessels, nerves, glands

  • Muscularis externa

    • Inner circular layer

    • Outer longitudinal layer

    • Produces peristalsis

  • Adventitia (outermost)

    • Dense CT anchoring esophagus to surrounding tissues (unlike serosa found in abdominal GI organs)

  • Lumen morphology

    • Soft-tissue walls → lumen is collapsed & irregular when empty

    • Expands & conforms to bolus shape during swallowing

Deglutition (Swallowing)

  • Definition: coordinated reflex that moves a bolus from oral cavity to stomach

Initiation Phase – Oral/Voluntary

  • Tongue pushes bolus posteriorly against oropharynx → activates stretch/pressure receptors in pharyngeal wall

Pharyngeal Phase – Reflex (involuntary)

  • Triggered by sensory input from pharynx

  • Simultaneous events:

    1. Upper esophageal sphincter relaxes (opens)

    2. Epiglottis pulled downward to cover glottis (laryngeal opening)

    • Epiglottis = cartilaginous flap; "epi" = above, "glottis" = vocal opening

    • Prevents aspiration; failure ➞ choking → cough reflex

    • Additional safety: vestibular folds/membranes above vocal cords can trap stray material

    1. Soft palate elevates → seals nasopharynx, preventing bolus entry into nasal cavity

    2. Pharyngeal (superior, middle, inferior) constrictor muscles contract sequentially behind bolus → peristaltic wave toward esophagus

Esophageal Phase – Reflex (involuntary)

  • UES re-closes once bolus passes

  • Esophageal peristalsis propels bolus toward stomach

  • LES reflexively relaxes on approach, then re-contracts after entry to maintain barrier against reflux

Clinical & Integrative Notes

  • Acid reflux (GERD)

    • LES incompetence → gastric acid backflow → mucosal irritation ("heartburn")

  • Protective adaptation

    • Stratified epithelium in mouth, pharynx, esophagus shields against abrasive solid food

    • Stomach switches to simple columnar epithelium specialized to withstand acidity and secrete mucus

  • Respiratory interaction

    • Pharynx serves both digestive & respiratory tracts → coordination via epiglottis is critical

    • Swallow–breath coordination essential; dysphagia increases aspiration risk

  • Equalisation of middle-ear pressure (auditory tube)

    • Demonstrates GI/respiratory structures’ role in auditory function & real-world phenomena (air travel pressure changes)