Swallowing(Deglutition)

• Voluntary Stage (oral stage) This initiates the swallowing process• Involuntary Pharyngeal stage This is involuntary and constitutes passage of food through pharynx into esophagus. Esophageal stage This is also involuntary phase that transports food from the pharynx to the stomach 

Voluntary stage(oral)Food is voluntarily squeezed or rolled posteriorly into the pharynx by pressure of the tongue upward and backward against the palate.

Pharyngeal stageWhen the bolus enters the posterior mouth and pharynx it stimulates epithelial swallowing receptor areas all around the opening of pharynx and impulses from these pass to the brain stem to initiate a series of automatic pharyngeal muscle contractions.1. Soft palate is raised upwards closing the posterior nares. 2. The palatopharyngeal folds on each side of pharynx are pulled medially to

approximate each other forming a slit allowing food that has been masticated sufficiently to pass with ease.

3. Vocal cords are approximated and larynx is pulled upward and anteriorly by neck muscles.

4. Epiglottis swings backward over the opening of larynx. The upward movement of larynx also pulls up and enlarges the opening of esophagus. The upward movement of the larynx also lifts the glottis out of the main stream of food flow, so that the food mainly passes on each side of the epiglottis rather than over its surface

• Once the larynx is raised and the pharyngo esophageal sphincter becomes relaxed the entire muscular wall of pharynx contracts beginning in superior part and then spreading downward which propels the food by peristalsis into esophagus.

Nervous Regulation

Impulses go through the sensory portions of trigeminal nerve and glossopharyngeal nerve to the swallowing center in the lower pons and medulla

 

• The motor impulses from the swallowing center go through the fifth, ninth, tenth and twelfth cranial nerves to the pharynx and esophagus.

• The entire pharyngeal stage of swallowing occurs in less than 6 seconds.

• During the pharyngeal stage the swallowing center inhibits respiratory center interrupting respiration for a fraction of second which is hardly noticeable

Esophageal Stage

• The esophagus functions primarily to conduct food from the pharynx to the stomach.

• Esophagus exhibits two types of peristalsis Primary peristalsis Secondary peristalsis

Receptive Relaxation of Stomach

• When the esophageal peristaltic wave approaches the stomach, a wave of relaxation transmitted through myenteric inhibitory neurons causes the stomach to relax before the entry of food.

Function of lower Esophageal Sphincter

• This sphincter normally remains constricted but when the peristaltic swallowing wave passes down the esophagus, there is receptive relaxation of lower esophageal sphincter ahead of the peristaltic wave.

• The tonic contraction of LES prevents the reflux of stomach contents into the esophagus.

• Another factor that helps to prevent reflux is a valvelike mechanism of a short portion of the esophagus that extends slightly into the stomach. Increased intraabdominal pressure caves the esophagus inward at this point. This valvelike closure of the lower esophagus helps to prevent high intra-abdominal pressure from forcing stomach contents backward into the esophagus e.g walking, coughing,