Physiology of Deglutition

Dr. Krishna Koirala

2016-12-05

• Mechanism which transmits liquids or solids from the mouth to the stomach via the pharynx and esophagus without entering the respiratory tract

• During swallowing, muscles are activated in an orderly sequence

– Controlled by complex neuromuscular interaction

– Triggered by volitional cortical drive or peripheral sensory input

– Sequential cascade does not alter after it starts

• Neural networks that are responsible for this automatic swallowing process are called central pattern generator

• Sites – Brainstem, nucleus tractus solitarius ,

nucleus ambiguus, reticular formation

Stages1. Oral stage (lasts for 1 second, voluntary)

–Preparatory phase

–Propulsive phase

2. Pharyngeal Stage (1 second, involuntary)

3. Esophageal Stage (8-20 sec, involuntary )

Oral preparatory stage

• Processing of the bolus to render it swallowable

• Solid food chewed, lubricated with saliva &

converted to a bolus

• Requires coordinated movement of lips, cheeks,

jaws and tongue against a closed oropharyngeal

isthmus

Nerves involved : V , VII, X, XII

Liquid - about 1 second, Solids - 5-

10 seconds

Oral propulsive stage• Propelling of food from the oral cavity into

the oropharynx

• Bolus propelled backwards by pressing of tongue against hard palate. Approximation of tongue against hard palate starts with tip of tongue and moves back

• Ends when food bolus crosses anterior

tonsillar pillars

Oral propulsive stage

Pharyngeal stage

1. Nasopharyngeal isthmus closed: soft palate touches Passavant’s ridge

2. Elevation of larynx negative pressure in hypopharyngeal lumen (suction pump)

3. Oropharyngeal isthmus closed: tongue base touches palate

4. Closure of larynx: (Laryngeal Tier Mechanism)

• Below upwards

– True vocal cords approximate

– False cords approximate

– Aryepiglottic folds approximate

• Temporary cessation of respiration

• Epiglottis falls back over laryngeal inlet due to laryngeal elevation and tongue pressure (lid effect)

Nasopharyngeal isthmus closed

Elevation & closure of Larynx

Oropharyngeal isthmus closed

5. Posterior retraction of tongue base ( tongue driving force)

6. Pharyngeal constrictors

contract

7. Elevation of pharynx

8. Opening of

cricopharyngeal sphincter

Opening of cricopharynx

Esophageal stage1. Closure of cricopharyngeal sphincter

2. Opening and descent of larynx

3. Primary peristalsis

– Large amplitude, propulsive, 8-9 seconds

4. Secondary peristalsis : arise locally in response to distension

– Small amplitude, propulsive, for food remnants

5. Tertiary Esophageal contractions6. Relaxation of lower esophageal sphincter

– Food bolus enters stomach

Closure of cricopharynx Opening & descent of larynx

Esophageal Peristalsis

Bolus enters stomach

Neural Mechanism• Afferents : V, IX & X cranial nerves

• Deglutition centre: Medulla oblongata

• Efferents

– X, XI & XII cranial nerves tongue, pharynx, larynx and esophageal muscles

• Cessation of respiration

– Connection between deglutition and respiration centres in medulla

• CN V : Chewing

• CN VII : Sensation to oropharynx & taste to anterior 2/3 of tongue

• CN IX : Taste to posterior 1/3rd of tongue, sensory and motor functions of the pharynx

• CN X : Taste to oropharynx, sensation and motor function to larynx and laryngopharynx . Airway protection

• CN XII : Contains motor fibers that primarily innervate the tongue

Factors preventing reflux• Anatomical– Lower esophageal sphincter contraction

– Pinch cock action of right crus of diaphragm– Lower esophageal mucosal folds (valvular)

– Oblique esophageal entry into stomach

– Oblique gastric muscle around lower esophagus

– Abdominal pressure > gastric pressure & intra-thoracic pressure

• Physiological

– Unidirectional esophageal

peristalsis

– Gastric emptying