Transcript Deglutition Reflex – Lecture by Dr Amna Tahir

DEGLUTITION REFLEX
DR AMNA TAHIR
ASSISTANT PROFESSOR
PHYSIOLOGY DEPARTMENT
Stages of Swallowing (Deglutition)
• Oral stage (voluntary)
• Pharyngeal stage
• Esophageal stage
Swallowing (Deglutition)
• Vagus & glossopharyngeal nerves for upper
1/3
• Vagus nerve innervates the lower 2/3
Swallowing (Deglutition)
Brain Stem (medulla & pons)
(swallowing center)
CN V, IX, X & XII
Swallowing (Deglution)
Swallowing can be divided into:
Voluntary stage of swallowing
 Bolus  voluntarily squeezed or rolled posteriorly against
the palate
 Swallowing cannot be stopped
Pharyngeal stage of swallowing
 Bolus reaches posterior mouth & pharynx  stimulates
receptors  initiate series of automatic pharyngeal
muscle contraction
Automatic pharyngeal muscle contraction:
Soft palate is pulled upward and prevents the reflux of
food to nasal cavity
Palatopharyngeal folds are pulled medially to
approximate each other – form a saggital slit
Vocal cords are approximated
Larynx is pulled upward & anterior by neck muscles
Epiglottis swing backward over the opening of larynx
Automatic pharyngeal muscle contraction:
Upward movement of larynx & enlargement the
opening of esophagus
Upper 3-4cm of esophagus relaxes
Muscular wall of pharynx contracts to push the food
downward (propulsive contraction)
N.B. pharyngeal stage lasts for < 2 sec
Swallowing (Deglution)
Esophageal stage of swallowing
 Conducts food rapidly to the stomach
 Two types of peristaltic movements:
1° peristalsis:
– continuation of a peristaltic wave
– begins in pharynx & spreads into esophagus
– passes in 8-10 sec
2° peristaltic waves:
– results from the distention of esophagus
– begins if the 1° wave failed to push the food down
Deglutition (Swallowing)
Figure 22.13a-c
Receptive relaxation of stomach
• As the waves of peristalsis pass thru esophagus
to stomach, a wave of relaxation precedes the
peristalsis, which transmitted thru myenteric
inhibitory neurons
Function of lower esophageal sphincter
(Gastroesophageal sphincter)
• above the junction of esophagus with stomach by
3cm
• remains tonically constricted
• peristaltic swallowing wave passes down esophagus
 receptive relaxation of gastro-esophageal
sphincter  allow food go easily to stomach
• Sphincter does not relax satisfactorily  condition
called achalasia
Lower Esophageal Sphincter
Esophageal reflux can be prevented by:
• Gastro-esophageal sphincter
• Valve-like mechanism: short portion of the
esophagus that extends beneath the
diaphragm before opening into stomach
Deglutition (Swallowing)
Figure 22.13d, e
the factors that contribute to the
competence and tone of the lower
esophageal sphincter
• Lower esophageal sphincter (LOS) is formed by the
lowest 2 – 4cm segment of the esophagus
• - Physiological sphincter
• Resting pressure: 15 – 25mmHg (20 – 30 cmH2O)
above gastric pressure Prevents reflux
• - Barrier pressure = LOS P – intragastric P
(10cmH2O @ rest) Normally Barrier P =
25cmH2O, reflux at <13cmH2O ↑intraabdominal P (pregnancy) will ↑intragastric P
→ ↓barrier P
Neural Control
• Internal relaxation- contraction cycling
(smooth mm) coordinated by medulla via
vagus
• External portion of sphincter (crura) supplied
by phrenic nerve
Factors contributing to
competence/tone
1-Tonic contraction of circular muscle fibers
2-Oblique gastro-esphageal angle
forms a mucosal flap-valve mechanism
3-Crura of diaphragm
forms pinch-cock mechanism
4- LOS is intra-abdominal
- Enhances LOS tone with positive IAP rather
than negative ITP
-↑LOS tone with cough/sneeze
5. Hormones
- ↑LOS tone: gastrin, motilin, α-adrenergic
stimulation, oestrogen
• - ↓LOS tone: secretin, glucagon, VIP,
GIP,PROGESTONE
Gastro esophageal reflux
Gastro esophageal reflux is a condition where
the acidic content of the stomach regurgitates
back into the esophagus. The distal esophageal
mucosa is non glandular in type (it is squamous
epithelium), therefore, it can easily be damaged
by chronic acid reflux.
-- TO prevent this, there are several mechanisms
in place
• The lower oesophageal sphincter (LOS) is tonically active but
relaxes on swallowing. The tonic activity of the LOS between
meals prevents reflux of gastric contents into the oesophagus.
• The prominent smooth muscle of the lower oesophagus acts
as a internal phincter to prevent reflux.
• The right crus of the diaphragm which surrounds the
oesophagus exerts a pinch-cock like action on the oesophagus
to prevent reflux (external sphincter).
• The oblique or sling fibers of the stomach wall create a flap
valve that helps close off the esophago-gastric junction and
prevent regurgitation when intra-gastric pressure rises.
• Another factor that helps to prevent reflux is a valve like
mechanism of a short portion of the esophagus that extends
slightly into the stomach. Increased intra-abdominal pressure
caves the esophagus inward at this point. Thus, this valve like
closure of the lower esophagus helps to prevent high intraabdominal pressure from forcing stomach contents backward
into the esophagus
CAUSES OF DYSPHAGIA
Oral( painful mastication)
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Oral malignancy
Tonsillitis
Herpes simplex
Aphthous ulceration
stomatitis
Pharyngeal
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Following cerebrovascular disease ( stroke)
Bulbar and pseudo bulbar palsy
Pharyngeal malignancy
Myasthenia gravis
Motor neuron disease
Pharyngeal diverticulum
esophagus
Motility disorders
• Achalasia
• Diffuse spasm
• Scleroderma
Extrinsic pressure
Mediastinal mass lesion
• Bronchogenic carcinoma
• Dilated left atrium
• Aortic aneurysm
• Foreign bodies
• goitre
Intrinsic pressure
• Benign esophageal stricture
• Carcinoma
 webs and rings
• Lower esophageal ring
ACHALASIA CARDIA
ACHALASIA CARDIA
• It is a disease of an unknown etiology
characterized by aperistalsis in the body of
oesophagus and failure of relaxation of lower
oesophageal sphincter on initiation of
swallowng .
• The food collects in capacious oesophagus
resulting in dilatation of oesophagus
Pathophysiology
Clinical features
• Dysphagia
• Regurgitation
• Retrosternal chest pain
Investigation
• X-ray chest
• Barium swallow
• Oesophagoscoy
Treatment
Endoscopic
 Pneumatic dilatation
 Botulism
Surgical