Lecture on Deglutition (Swallowing)

Importance of Deglutition

• Essential for nutrient absorption from food (e.g., pizza).
• Involves moving food from the oral cavity to the stomach.

Phases of Deglutition

• Oral Phase
• Pharyngeal Phase
• Esophageal Phase

Oral Phase

• Anatomy & Boundaries of the Oral Cavity

  • Anterior: Oral vestibule.
  • Posterior: Palatoglossal arch.

• Depression of the Mandible

  • Muscles involved: Lateral pterygoid, digastric (anterior belly), mylohyoid, geniohyoid.
  • Innervation: Cranial nerve V (Trigeminal nerve, V3 mandibular division), Cervical plexus (C1 ramus).

• Elevation of the Mandible

  • Muscles involved: Masseter, temporalis, medial pterygoid.
  • Innervation: Cranial nerve V (Trigeminal nerve, V3 mandibular division).

• Mechanical Digestion

  • Teeth functions: Incisors (cutting), canines (tearing), molars (grinding).

• Salivation

  • Types: Intrinsic (10%), Extrinsic (90% - parotid, submandibular, sublingual).
  • Functions: Lubricate food, begin chemical digestion (salivary amylase for carbohydrates, lingual lipase for fats).

• Bolus Formation

  • Tongue muscles: Intrinsic (form central trough), Extrinsic (elevate tongue).
  • Innervation: Cranial nerve XII (Hypoglossal nerve).

Pharyngeal Phase

• Sensory Activation

  • Initiated by bolus touching the palatoglossal arch.
  • Innervation: Cranial nerve IX (Glossopharyngeal nerve).

• Preventing Nasopharyngeal Entry

  • Elevation of uvula and soft palate (levator veli palatini, tensor veli palatini).
  • Innervation: Cranial nerve X (Vagus nerve), Cranial nerve V (Trigeminal nerve, V3).

• Preventing Laryngeal Entry

  • Approximation of vocal cords (lateral cricoarytenoids, arytenoid muscles).
  • Epiglottis retroversion.

• Ensuring Pharyngeal Passage

  • Muscles: Palatoglossus, palatopharyngeus (approximate walls).
  • Outer longitudinal muscles: Styloglossus, salpingopharyngeus, palatopharyngeus (elevate pharynx and larynx).
  • Inner circular muscles: Pharyngeal constrictors (superior, middle, inferior).

• Upper Esophageal Sphincter (UES)

  • Muscle: Cricopharyngeus (part of inferior pharyngeal constrictor).
  • Function: Relaxation allows bolus entry into the esophagus.

Esophageal Phase

• Peristalsis

  • Primary: Continuation of pharyngeal peristalsis.
  • Innervation: Cranial nerve X (Vagus nerve).

• Lower Esophageal Sphincter (LES) Function

  • Allows bolus entry into the stomach.

• Secondary Peristalsis

  • Triggered by bolus stuck in the esophagus.
  • Local reflex via the myenteric plexus.

Conclusion

• Deglutition is a complex, coordinated process involving multiple phases and nerve innervations to ensure safe and efficient swallowing.
• Critical for nutrient absorption and preventing aspiration.