Download Swallowing - MBBS Students Club

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 stage
When 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,