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

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

Movements of GITIngestion of food-II

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

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

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 Mahmood6

Swallowing (Deglutition)

• Three stages;–Voluntary Stage–Pharyngeal Stage (Involuntary)–Esophageal Stage (Involuntary)

Esophageal Stage (Involuntary)

• Function: Conduction of food• Peristalsis: 2 types

–Primary–Secondary

• Musculature of Esophagus–Striated–Smooth

Peristalsis of Esophagus• Primary Peristalsis:

Continuation of Peristaltic wave of Pharynx

8-10 seconds

↓ Stomach

Upright: 5-8 seconds

Peristalsis of Esophagus• Secondary Peristalsis

If Primary Peristalsis failsdistension→

1.vagal afferent fibers

↓ medulla

↓ vagus +glossopharyngeal nerve2. simulation of intrinsic neuronal circuits

Assessment Q. No.5 • What is the roll of Secondary peristalsis in

normal Swallowing?

© Prof. Dr. Rashid Mahmood 11

Esophageal Stage (Involuntary)

Function: Conduction of foodPeristalsis: 2 types

PrimarySecondary

• Musculature of Esophagus– Striated– Smooth

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

Summary of stages

of swallowing

1. Voluntary

stage

2. Pharyngeal stage

2. Pharyngeal stage (Contd….)

Epiglottis Opening of larynx

Pharyngeal stage↓

Esophageal stage

Esophageal stage

Assessment Q. No.6 • In which stage of swallowing respiration

stops? What is its mechanism?

© Prof. Dr. Rashid Mahmood 19

Esophagus → Stomach

• Relaxation of lower esophageal sphincter

• Receptive relaxation of stomach

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

Lower esophageal sphincter

Three components:1.Internal sphincter2.External Sphincter3.Phrenoesophageal ligament

Nervous Control of Lower esophageal sphincter

Cholinergic Fibers

• Tonic Constriction

VIP, NO

• Inhibitory effect

Vagus nerve

Receptive Relaxation of the Stomach

Esophageal peristaltic wave → Myenteric inhibitory Neurons → Relaxation of entire stomach (& even

duodenum)

Stages of deglutition

Assessment Q. No.7 • What is the mechanism of Receptive

Relaxation of the Stomach?

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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

Assessment Q. No.8 • What is the role of Sympathetic nervous

system stimulation in control of Gastro-esophageal Sphincter?

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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

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