VPB 121: Veterinary Physiology - II (2+1)

STAGES OF SWALLOWING

• Pharyngeal stage - Phryngeo oesophageal sphincter
• Oesophageal stage - Significance of lower esophageal sphincter.

Pharyngeal stage

• Relaxation of pharyngeo oesophageal sphincter.
• Peristaltic contractions of the pharynx to propel the food bolus from the base of the tongue into laryngopharynx.
• Propulsion of the bolus via relaxed pharyngeo oesophageal sphincter to the esophagus.
• Pharyngeo oesophageal sphincter
  • It is also known as upper oesophageal sphincter formed by the cricopharyngeal muscle and oesophageal circular muscle.
  • As the bolus proceeds to upper oesophagus, simultaneous contractions of this sphincter to a closed state to initiate next stage of swallowing reflex.
  • The bolus travels from cranial esophagus to caudal oesophagus via gastro esophageal junction.
  • Gastro esophageal junction is guarded by a lower oesophageal sphincter.
  • Reflex, contraction of the oesophageal muscles to propel the bolus down.
  • This reflex is completed by vagus.
  • Accumulation of several boluses in the oesophagus causes local myogenic stimulus initiates more powerful peristalsis to push the food to gastro oesophageal junction.

Oesophageal stage

• Lower oesophageal sphincter
  • It differentiates esophagus and stomach.
  • Physiologically is in a high pressure zone.
  • The incoming bolus exert force to open this sphincter.
  • This is an active reflex mediated by vagus to increase oesophageal pressure.
  • Synchronized act of relaxation of lower oesophageal sphincter with oesophageal wave propel the bolus into the stomach.