this lecture relates to physiology of ingestion of food, and includes mastication (chewing) and deglutition (swallowing)

1. Mastication and Deglutition-II
•A 42-year-old woman reports difficulty in swallowing solid foods;
liquids are less difficult to swallow. She frequently regurgitates
after eating. When the recumbent patient underwent fluoroscopy
after a barium swallow, her lower esophagus was somewhat
dilated compared with normal, but her upper esophagus was of
normal caliber. Subsequent swallows initiated by the patient
showed that the barium was cleared from the esophagus very
slowly. Monomeric studies showed that resting pressure in the
lower esophageal sphincter decreased after a swallow. The
patient was treated with forceful dilation of the lower esophageal
sphincter. The patient’s ability to swallow solid food was
dramatically improved after the dilation procedure.
Prof. Dr. Rashid Mahmood

2. 1. What is the mechanism of slow rate of
barium clearance from the
esophagus?
2. What will be the effect on esophageal
musculature of this patient?
3. How the above-mentioned therapy for
this patient’s improved swallowing
difficulties

3. 3
Movements of GIT
Ingestion of food-II

4. Recap
• Ingestion of food involves two processes: Mastication
(Chewing) & Swallowing (Deglutition)
• Teeth cut & grind the bolus of food
• Mastication is brought about by Muscles of Chewing,
Controlled mainly by 5th Nerve.
• Chewing Reflex, initiated by bolus of food in mouth results in
reflex inhibition of Muscles of Mastication. This results in
Stretch Reflex, causing their Rebound Contraction
• Swallowing (Deglutition) occurs in three stages: Voluntary
Stage, Pharyngeal Stage and Esophageal Stage
• Voluntary Stage involves mainly tongue, pushing the bolus of
food in pharynx
• Pharyngeal Stage is Involuntary; in this stage swallowing
reflex results in Series of Automatic Pharyngeal Muscle
Contractions

5. Objectives
• Specific Objectives: At the end of the lesson
student will be able to:
• Explain the Esophageal Stage of swallowing
• Understand how food is transferred to stomach
• Classify types of peristalsis of esophagus
• Describe physiological anatomy of oesophagus
• Describe the Nervous Control of Lower esophageal
sphincter
• Describe the mechanism of Protection of
Esophageal Reflux
Goal/Aim: To give the understanding of the
physiology of Mastication and Deglutition

6. Lesson Contents
• Summary of voluntary and pharyngeal
stage of swallowing
• Function of Esophagus
• Peristalsis of Esophagus
• Musculature of Esophagus
• Gastro-esophageal Sphincter
• Nervous Control of Lower esophageal
sphincter
• Receptive Relaxation of the Stomach
• Protection of Esophageal Reflux
© Prof. Dr. Rashid Mahmood
6

7. Swallowing (Deglutition)
• Three stages;
–Voluntary Stage
–Pharyngeal Stage (Involuntary)
–Esophageal Stage (Involuntary)

8. Esophageal Stage (Involuntary)
• Function: Conduction of food
• Peristalsis: 2 types
–Primary
–Secondary
• Musculature of Esophagus
–Striated
–Smooth

9. Peristalsis of Esophagus
• Primary Peristalsis:
Continuation of Peristaltic wave of Pharynx
8-10 seconds
↓
Stomach
Upright: 5-8 seconds

10. Peristalsis of Esophagus
• Secondary Peristalsis
If Primary Peristalsis fails
distension→
1.vagal afferent fibers
↓
medulla
↓
vagus +glossopharyngeal nerve
2. simulation of intrinsic neuronal circuits

11. Assessment Q. No.5
• What is the roll of Secondary peristalsis in
normal Swallowing?
© Prof. Dr. Rashid Mahmood 11

12. Esophageal Stage (Involuntary)
Function: Conduction of food
Peristalsis: 2 types
Primary
Secondary
• Musculature of Esophagus
– Striated
– Smooth

13. Musculature of Esophagus
• Striated
• Pharyngeal wall and upper third of
esophagus
• Skeletal nerve fibers in 9th
, 10th
cranial
nerves
• Smooth
• Lower 2/3rd
of esophagus
• Vagus nerve → Myenteric Nervous
System

14. Summary of
stages of
swallowing
1. Voluntary
stage

15. 2. Pharyngeal
stage

16. 2. Pharyngeal stage (Contd….)
Epiglottis Opening of larynx

17. Pharyngeal stage
↓
Esophageal stage

18. Esophageal stage

19. Assessment Q. No.6
• In which stage of swallowing respiration
stops? What is its mechanism?
© Prof. Dr. Rashid Mahmood 19

20. Esophagus → Stomach
• Relaxation of lower
esophageal sphincter
• Receptive relaxation of
stomach

21. Gastro-esophageal Sphincter
• Lower Esophageal Sphincter
• Tonically constricted
• Protection of Esophageal Reflux
• Receptive Relaxation
• Esophageal mucosa not able to resist
gastric secretions except Lower 1/8th
• Valve-like closure of distal end of
Esophagus; ↑ intraabdominal pressure

22. Lower esophageal sphincter
Three components:
1.Internal sphincter
2.External Sphincter
3.Phrenoesophageal ligament

23. Nervous Control of Lower
esophageal sphincter
Cholinergic Fibers
• Tonic Constriction
VIP, NO
• Inhibitory effect
Vagus nerve

24. Receptive Relaxation of the Stomach
Esophageal peristaltic wave
→ Myenteric inhibitory Neurons
→ Relaxation of entire stomach (& even
duodenum)

25. Stages of deglutition

26. Assessment Q. No.7
• What is the mechanism of Receptive
Relaxation of the Stomach?
© Prof. Dr. Rashid Mahmood 26

27. Take home points
– Esophageal Stage is the 3rd
stage of swallowing & is involuntary.
– Two types of Peristalsis of Esophagus function to conduction of food from pharynx to
stomach.
– Primary Peristalsis is the continuation of Peristaltic wave of Pharynx that pushes the
food into stomach through Gastro-esophageal Sphincter.
– If Primary Peristalsis fails, then distension of Musculature of Esophagus results in
Secondary Peristalsis
– Upper 3rd
Musculature of Esophagus is Striated muscle, and lower 2/3rd
is Smooth
muscle
– Esophageal peristaltic wave ends in Receptive Relaxation of the Stomach through
Myenteric inhibitory Neurons. This occurs before food reaches the stomach.
– Lower Esophageal Sphincter (Gastro-esophageal Sphincter) is guarded by Internal
and External sphincters, and normally remains Tonically constricted under the effect of
Cholinergic Fibers of Vagus nerve
– It is only dilated during passage of the food; the inhibition is brought about by VIP and
NO secreted by Vagal fibers
– Tonic constriction of Gastro-esophageal Sphincter performs important function of
protection of Esophageal Reflux. This protection is aided by Valve-like closure of distal
end of Esophagus when intraabdominal pressure increases.
© Prof. Dr. Rashid Mahmood

28. Assessment Q. No.8
• What is the role of Sympathetic nervous
system stimulation in control of Gastro-
esophageal Sphincter?
© Prof. Dr. Rashid Mahmood 28

29. Learning resources
• Guyton and Hall (Text book of physiology),
13th
edition, P.708-709
• Ganong (Text book of physiology), 24th
Edition, P. 500-501
• Walter F. Boron Medical Physiology, 2nd
Edition, P.890-891
© Prof. Dr. Rashid Mahmood 29

30. © Prof. Dr. Rashid Mahmood 30