Physiology of Deglutition
Dr. Rekha Limbu
Lecturer
Department of Physiology 10.02.2023
Learning objectives
o Definition of swallowing
o Stages of swallowing
o Deglutition/ swallowing reflex
o Motor disorders of esophagus
Deglutition (Swallowing)
o The process by which food bolus moves from mouth to stomach
via pharynx & esophagus.
o involves co-ordinated activity of muscles of oral cavity, pharynx,
larynx & esophagus.
o partly under voluntary control & partly reflexive in nature.
Stages of Swallowing
1. Voluntary stage- initiates swallowing process
2. Involuntary stage:
o Pharyngeal (passage of food through pharynx into
esophagus)
o Esophageal (transports food from pharynx to stomach)
Stages of Swallowing (contd..)
1. Voluntary stage of swallowing
When food is ready for
swallowing → it is voluntarily
squeezed or rolled posteriorly
into pharynx by pressure of
tongue upward & backward
against palate.
Ref: Ganong 26th edition
Stages of Swallowing (contd….)
2. Pharyngeal stage of swallowing
Bolus of food in posterior mouth & pharynx
(+) epithelial swallowing receptor areas
around pharyngeal opening (tonsillar pillars)
Impulses are transmitted through
trigeminal & glossopharyngeal nerves into NTS (medulla)
Swallowing center (medulla & lower pons)
Motor impulses are transmitted through 5th, 9th, 10th & 12th CN to
pharynx & upper esophagus
initiate a series of automatic pharyngeal muscle contractions
SWALLOWING REFLEX
Fig: Swallowing mechanism. Ref: Guyton 13th edition
Stages of Swallowing (contd….)
o Soft palate is pulled upward to
close posterior nares.
o Palatopharyngeal folds on each
side of pharynx are pulled
medially forming a sagittal
slit through e food pass into
posterior pharynx. Palatopharyngeal
arch
Stages of Swallowing (contd….)
o Tight approximation of vocal
cord + larynx is pulled upward
& anteriorly by neck muscles+
Epiglottis swing backward
over opening of larynx
o Upward movement of larynx
pulls up & enlarges opening to
esophagus.
Stages of Swallowing (contd….)
o Upper esophageal sphincter (UES) relaxes.
o Pharyngeal muscle contraction starts
(peristalsis) from superior part of
pharynx, then spreading downward over
middle & inferior pharyngeal areas →
forces food into upper esophagus
Between swallows, UES remains
contracted (prevents air from going
into esophagus during respiration)
Effect of Pharyngeal Stage of Swallowing on Respiration
Pharyngeal stage of swallowing occurs in < 6 sec→ temporary
arrest of respiration for a few seconds (Deglutition apnea)
MECHANISM
Swallowing center inhibits respiratory center of medulla
during this time, halting respiration at any point in its cycle
to allow swallowing to proceed.
Stages of Swallowing (contd….)
3. Esophageal stage of swallowing
o Food bolus is propelled through esophagus by propulsive
movements known as PERISTALSIS (a ring like contraction of
circular smooth muscle that moves forward pushing bolus into
relaxed area)
Two types of peristaltic movements:
a. Primary peristalsis
b. Secondary peristalsis
Stages of Swallowing (contd….)
a. Primary peristalsis
o continuation of peristaltic wave that begins in pharynx &
spreads into esophagus.
o In an upright position, liquids & semisolid foods fall by gravity
to lower esophagus ahead of peristaltic wave.
b. Secondary peristalsis
o If primary peristaltic wave fails to move all food that has entered
esophagus into stomach→ secondary peristaltic waves result from
distension of esophagus by retained food.
o initiated partly by MYENTERIC PLEXUS + partly by reflexes that
begin in pharynx.
Stages of Swallowing (contd….)
When a peristaltic swallowing wave passes down esophagus, “receptive
relaxation” of lower esophageal sphincter occurs ahead of peristaltic
wave, which allows easy propulsion of swallowed food into stomach.
Lower Esophageal Sphincter (LES)
o At the lower end of
esophagus (3cm above its
juncture ē stomach),
circular muscle of
esophagus fxns as a lower
esophageal sphincter
o Normally LES remains
tonically constricted ē an
intraluminal pressure of 30
mmHg.
Lower Esophageal Sphincter (LES) contd……
o Tonic activity of LES between meals
prevents reflux of gastric contents
into esophagus.
o Tone of LES is under neural control;
LES contract via release of Ach from
vagal endings & relaxes via release of
NO & VIP from interneurons
innervated by other vagal fibers.
Applied Physiology
Motor Disorders of Esophagus
o Achalasia
o Gastroesophageal reflux disease (GERD)
Achalasia
Normal Achalasia
o ↑resting LES tone & incomplete relaxation on swallowing.
o Rx: pneumatic dilation of the sphincter or myotomy.
Inhibition of Ach release by inj. of botulinum toxin into LES.
Gastroesophageal Reflux Disease (GERD)
LES Incompetence
o Symptoms: heartburn &esophagitis; ulceration & stricture of
esophagus due to scarring.
o Rx: H2-receptor blockers or proton pump inhibitors
REFERENCES
1. Text book of medical physiology Guyton and hall, 13th edition.
2. Ganong’s review of medical physiology, 26th edition.
