Deglutition Phases

Hi, let’s learn something about deglutition

Deglutition (swallowing) is the process by which food moves from mouth into the stomach.

There are 3 stages or phases of deglutition

1) Voluntary stage

2) Pharyngeal stage

3) Esophageal stage

Also known as oral stage initiates the swallowing process

In this stage the bolus from mouth passes into pharynx by means of series of actions.

It is involuntary and constitutes the passage of food through the pharynx into the esophagus.

As pharynx communicates with nose, mouth, larynx and esophagus, in this stage bolus from pharynx can enter into four paths-

                       

i) Back into mouth-

It is prevented by-

a) Positioning of tongue against the soft palate

b) High intraoral pressure developed by the movement of tongue.

ii) Upward into nasopharynx –

It is prevented by elevation of soft palate along with its extension called uvula

iii) Forward into larynx

It is prevented by-

a) Approximation of the vocal cords

b) Forward and upward movement of larynx

c) Backward movement of epiglottis to seal the glottis

  All these movements arrest respiration for few seconds and is called deglutition apnea.

iv) Entrance of bolus into esophagus

            assisted by-a)Upward movement of larynx stretches the opening of esophagus.

b) Simultaneously upper 3 to 4 cm of esophagus relaxes. This part is called  upper esophageal sphincter

c) Peristaltic contractions start in pharynx due to the contraction of pharyngeal muscles

d) Elevation of larynx also lifts glottis away from the food passage

      Let’s see a summary of pharyngeal stage

i) The trachea is closed

ii) The esophagus is opened

iii) A fast peristaltic wave initiated by the nervous system of the pharynx forces the bolus of food into upper esophagus

iv) Entire process occurs in less than 2 seconds

It is also involuntary phase that transports food from the pharynx to stomach.

When bolus reaches the esophagus two types of peristaltic waves are initiated-

a) Primary peristaltic contractions

b) Secondary peristaltic contractions

a) Primary peristaltic contractions

  • After origin the peristaltic contractions pass down through the rest of esophagus, propelling the bolus towards stomach
  • Initially pressure becomes negative in upper part of esophagus
  • But immediately it becomes positive and increases up to 10 to 15 cm of H2O

b) Secondary peristaltic contractions

  • They start when the primary contractions are unable to propel the bolus into stomach.
  • Are induced by the distention of upper esophagus by bolus
  • These contractions pass down like the primary contractions, producing a positive wave.
  • When the bolus enters the oropharyngeal region the receptors in this region are stimulated.
  • Afferent impulses from this region pass via the glossopharyngeal nerve fibers to deglutition centre.
  • Deglutition centre is present at the floor of fourth ventricle
  • Impulses from deglutition centre travel through 5th , 9th, 10th and 12th cranial nerves and reach soft palate, pharynx and esophagus.
  • The reflex causes upward movement of soft palate to close nasopharynx and upward movement of larynx, to close respiratory passage so that bolus enters esophagus.
  • Now peristalsis occurs in esophagus pushing the bolus into stomach.

1)  Achalasia cardia

  • It is a neuromuscular disease characterized by accumulation of food substances in esophagus preventing normal swallowing.
  • It is due to failure of lower esophageal sphincter to relax during swallowing

2)Gastroesophageal Reflux disease

  • GERD is a disorder characterized by regurgitation of acidic gastric content through esophagus.
  • The regurgitated gastric content flows into pharynx or mouth
  • It is due to weakness or incompetence of lower esophageal sphincter

Contributed by Anuja Mandavkar

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