physiology of swallowing

1. 1
DR. Ramadan Saad

2. OBJECTIVES
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The student should be able to:
 Identify and describe the function of all parts of the oral
cavity.
 Identify and describe various salivary glands.
 Describe the compositions of the saliva.
 Identify the functions of the saliva.
 Discuss the control of salivary secretion.
 Discuss abnormal salivary secretion.
 Discuss the different mechanism involve in swallowing.

3. 3

4.  It is the passage of food from mouth to stomach.
 Started: Voluntary (Buccal phase)
 Completed: Involuntary (Pharyngeal & oesoph.)
 Controlled by: Deglutition Centre in M.O.
 Involves 3 phases
 Buccal (oral) 1 sec.
 Pharyngeal phase 2 sec.
 Oesophageal phase 8-10 sec.

5. 1. Buccal phase (Oral phase):
 Voluntary lasts for 1 sec.
 Passage of food from mouth to phary. by contraction
of myelohyoid muscle.
 Tongue moves upward & backwards
 To push bolus into pharynx.
Hard palate
Bolus
Tongue
Voluntary Phase

6. 2. Pharyngeal
phase:
 Involuntary lasts 2 sec.
 Passage of food from
pharynx to oesoph.
 When bolus is at
oropharyngeal junction
 It stimulates: Pressure
receptors

8. 2. Pharyngeal phase:
 Involuntary lasts 2 sec.
 Passage of food from pharynx to oesoph.
 When bolus is at oropharyngeal junction
 It stimulates: Pressure receptors
Soft palate (uvula):
 Moves upwards to close posterior nasal cavity to prevent food entrance into nasal cavity.
Respiration:
 Is inhibited
 i.e. reflex apnea for 2 sec.
Vocal cords:
 Approximated.
Larynx:
 Moves upwards & anterior to be covered by epiglottis.
Pharyngeal muscles:
 Fast pharyngeal peristalsis to  intrapharyngeal pressure to move bolus into oesophagus.
Upper oesophageal sphincter:
 Is relaxed
After this, the bolus is moved towards the oesophagus via peristalsis of the pharyngeal
constrictor muscles. Gravity makes very little contribution to this process and the main factors
affecting the speed of this are the viscosity and volume of the bolus.

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SWALLOWING

10. trachea
(windpipe)
glottis
During breathing, the
larynx is lowered and
the glottis is open.
pharynx
oesophagus
larynx
(voice-box)
air
What Happens During Breathing and
Swallowing?
Normally, air passes into
the trachea (windpipe)
while food passes into
the oesophagus.

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During swallowing, the
larynx is raised and the
glottis is covered by the
epiglottis. This prevents
food particles from
entering the trachea.
pharynx
trachea
(windpipe)
oesophagus
glottis
epiglottis
food
particles
larynx
(voice-box)
What Happens During Breathing and
Swallowing?

12. SWALLOWING
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3. Esophageal stage:
• Peristaltic waves push food through the
esophagus.
• The swallowing center triggers a primary
peristaltic wave.
• The peristaltic wave takes about 5 to 9 seconds
to reach the lower end of the esophagus.
• Progression of the wave is controlled by the
swallowing center, with innervation by means of
the vagus.

13. SWALLOWING
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3. Esophageal stage:
• Secondary peristaltic waves:
If the primary peristaltic wave fails to move into the
stomach all the food that has entered the
esophagus, secondary peristaltic waves result from
distention of the esophagus itself by the retained
food; these waves continue until all the food has
emptied into the stomach.
• Vagus and enteric nervous system
responsible for this peristalsis.

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When the vagus nerves to the esophagus are cut, the myenteric nerve plexus of the
esophagus becomes excitable enough after several days to cause strong secondary
peristaltic waves even without support from the vagal reflexes. Therefore, even after
paralysis of the brain stem swallowing reflex, food fed by tube or in some other way into
the esophagus still passes readily into the stomach.

15. Lower esophageal sphincter LES:
 Formed of circular muscle.
 It is Tonically contracted to prevent reflux of Hcl from stomach into oesoph.
 When peristalsis reaches lower end of esophagus, LES is relaxed to allow
bolus to pass into stomach.
 Relaxation of the LES is mediated by postganglionic parasympathetic inhibitory
neurons in the vagus nerve that release the neurotransmitters vasoactive
intestinal peptide (VIP) and nitric oxide (NO).
Achalasia
Failure of relaxation of LES.
Due to:
Damage of myenteric plexus.
 Accumulation of food in
esophagus.
 Distension of esoph.
LES incompetence
If LES is incompetent Hcl
reflux from stomach to esoph.
Heart burn.

16. Clinical Relevance - Dysphagia
• Dysphagia is the term for difficulty swallowing. It can
affect swallowing of both solid and liquid substances
depending on the cause. In addition to this, it can be due
to motility problems (an error of peristalsis) or obstruction
of the tube.
Common causes include:
• Stroke
• Tumours
• Xerostomia
• Oesophageal strictures
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17. REFERENCES
 Human Physiology, Lauralee Sherwood, seventh
edition.
 Text book Physiology by Guyton &Hall,13th
edition.
 Text book of Physiology by Linda S. Contanzo,
third edition.
 Physiology by Berne and Levy, sixth edition.
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