Lecture 4: The Pharynx and Esophagus

Structure of the Pharynx

• Three Parts:
  • Nasopharynx: Functions only in respiration.
  • Oropharynx and Laryngopharynx: Part of both the digestive and respiratory systems.
• Composition:
  • Made of skeletal muscle and lined by mucous membranes.

Deglutition (Swallowing)

• Involves saliva and mucus.
• Process:
  • Begins as bolus (chewed food) is pushed into the oropharynx.
  • Sensory nerves signal the deglutition center in the brainstem.
  • Soft palate lifts, closing nasopharynx; larynx is lifted, epiglottis covers glottis (respiratory opening).

Structure of the Esophagus

• Description:
  • Collapsible muscular tube behind the trachea, connects to the stomach.
  • Collapses when empty, unlike the trachea which is held open by cartilage rings.
• Layers:
  • Mucosa, submucosa, muscularis, and outer adventitia.
  • Difference from the serosa in the abdominal GI tract.
• Histology:
  • Stratified squamous epithelium makes up the mucosal layer.
  • Mucous glands in the submucosal layer.
  • Muscularis: Skeletal muscle at the top, mixed in the middle, smooth muscle at the bottom.
• Function: No digestion, only transport.
• Pierces the diaphragm at the hiatus:
  • Site of hiatal hernias: Stomach protrudes through the hiatus, leading to possible necrosis and peritonitis if constricted.

Swallowing Phases

1. Voluntary Phase:
   • Bolus is pushed into the oropharynx.
2. Pharyngeal Phase:
   • Bolus moves from pharynx to esophagus.
   • Epiglottis covers the glottis.
3. Esophageal Phase:
   • Peristalsis moves the bolus to the stomach.
   • Contraction behind bolus, relaxation in front.

Peristalsis

• Mechanism:
  • Circular fibers contract behind the bolus.
  • Longitudinal fibers relax in front.
  • Moves food like a constrictor snake swallows prey.
• Travel Time:
  • Food: 4-8 seconds.
  • Liquids: 1 second.
  • Lower esophageal sphincter opens to allow bolus into the stomach.

Gastroesophageal Reflux Disease (GERD)

• Causes:
  • Failure of lower sphincter to open or close.
  • Sphincter weakness leads to reflux.
• Prevention Tips:
  • Avoid large meals before lying down.
  • Avoid smoking, alcohol, certain foods (coffee, chocolate, tomatoes, etc.).
  • Use antacids like Tagamet, Pepcid AC, or Tums.
• Barrett's Esophagus:
  • Pathology:
    • Stomach acid alters esophageal lining to resemble gastric mucosa.
    • Increases risk of esophageal cancer.
  • Monitoring:
    • Requires periodic endoscopy and biopsy.

Esophageal Varices

• Description:
  • Varicose veins in the esophagus due to liver issues.
  • Veins are thin-walled, risk of rupture and bleeding.
• Symptoms: Difficulty swallowing, potential for severe bleeding.
• Treatments:
  • Medications to reduce bleeding.
  • Elastic bands to tie veins.
  • Shunts or liver transplant.

Lecture Goals

• Describe the three phases of swallowing.
• Define key terms: Deglutition, GERD, Hiatal Hernia, Esophageal Varices, Barrett's Esophagus, Peristalsis.
• Describe the histology of the esophageal mucosal layer.