Swallowing

Dr Wasif Haq

Introduction• To pass (food, drink, etc.) through the mouth to the

stomach by means of the pharynx and into the esophagus, while shutting the epiglottis.

• Also known as ‘deglutition’. • Swallowing reflex : Reflex caused by stimulation of

palate, fauces or posterior pharyngeal wall.

Phases of Swallowing• Swallowing 3 stages:• 1. Voluntary stage/Oral stage ; begins in

mouth, food pushed to Pharynx.• 2. Pharyngeal stage; involuntary, food passes

from pharynx to esophagus.• 3. Esophageal stage: also involuntary stage,

transports food from pharynx-esophagus to stomach.

1. Oral stage• Initiates the swallowing process.• Upward and backward pressure of tongue

against palate.• Lips are tightly closed to help build a tight seal.• Muscles of floor of mouth & tongue contract.• Nerves involved V (Trigeminal), VII (Facial) and

XII (Hypoglossal).

Voluntary/ Oral phase of swallowing: Initiated by contraction of muscles of tongue and floor of

mouth with tight seal maintained by lip closure, pushes the bolus posteriorly to Pharynx.

2. Pharyngeal Stage• Starts when food enters the posterior mouth &

pharynx and tonsillar pillars.• Swallowing receptors activation convey impulses to

brainstem (midbrain, pons & medulla oblongata) causing pharyngeal muscle contractions.

• Swallowing center inhibits respiratory center in this phase.

• The tongue pushes soft palate upwards causing closure of nasal opening at back and forcing Epiglottis to cover/close Larynx.

Pharyngeal stage: Food passes from Pharynx to Esophagus with larynx and trachea closure,

involuntary stage.

Steps of Pharyngeal Stage• 1. Upward movement of soft palate: Closure of

posterior nares to prevent entry of food into nasal cavity.

• 2. Medial approximation of Palatopharyngeal folds: Forms a slit (narrow opening) for food to pass. Large objects are blocked from swallowing.

• 3. Tight approximation of vocal cords: Larynx pulled upward & anteriorly by neck muscles, Epiglottis covers opening of Larynx, preventing food passage into trachea.

Steps of Pharyngeal Stage• 4. Relaxation of upper Esophageal sphincter: Larnyx

upward movement pulls Esophagus up causing increase in opening of Esophagus. With relaxation of U.E.S., the food travels to upper Esophagus.

• 5. Peristaltic movement by Pharynx: When Larynx is raised with relaxation of Pharyngoesophageal sphincter, muscles of Pharynx contracts and pushes food into Esophagus.

Nervous Regulation• Areas in the medulla and lower pons controlling

swallowing process are called Swallowing/ Deglutition center.

• Swallowing receptors convey impulses to Medulla oblongata (and to Tractus Solitarius) through sensory portion of V and IX cranial nerves.

• Motor impulses conveyed to Pharynx and upper Esophagus by V, IX, X and XII cranial nerves and some superior cervical nerves.

3. Esophageal Stage• Esophagus conveys food from Pharynx to stomach.• Two types of Peristaltic movements:• A. Primary Peristalsis (Continuation of Pharyngeal

peristaltic movement to Esophagus & Stomach)• B. Secondary Peristalsis (If primary peristaltic wave

fails to move food into stomach) Result from distention of Esophagus by retained food.

• Initiated by (i) Instrinsic myenteric nervous system in Esophagus &(ii) X afferent fibers from Pharynx to medulla & back through X efferent fibers & IX nerve

Esophageal stage: Primary peristaltic wave helps to convey food from Esophagus to stomach

Additional• In brainstem paralysis, swallowing reflex remains

intact because of compensatory excitation of Esophageal myenteric nervous system.

• Receptive relaxation of stomach: As peristaltic wave reaches lower Esophagus, stomach becomes relaxed to receive the food.

• Lower Esophageal Sphincter/ Gastroesophageal sphincter: Prevents reflux of stomach contents into Esophagus.

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