05-04-2023

GI MOTILITY

DR. KHALEEL AHMED MANIK MBBS, MD

PROFESSOR OF PHYSIOLOGY,
IIMSR, INTEGRAL UNIVERSITY, LUCKNOW.

MOVEMENTS OF GASTROINTESTINAL TRACT

 Mastication

 Deglutition

 Movements of small intestine

 Movements of large intestine

 Defecation

4. Lubrication and moistening of dry food by saliva so that, the bolus can
MASTICATION
be easily swallowed

Cutting the food substances into small particles and grinding them into a soft
5. Appreciation of taste of the food
bolus is known as mastication.

 Muscles and the movements of mastication

 Significance of mastication

 Masseter, temporal, pterygoids and buccinator muscles.

Mastication or chewing is the first mechanical process to which food is
subjected.  Movements which occur during mastication are closure and opening of
mouth, rotational movement and protraction and retraction of jaw.
1. Breakdown of food stuffs into smaller particles that increases surface area
and decreases particle size  Nervous control of mastication

2. Mixing of saliva with food substances thoroughly, that begins digestion of  The center for mastication is situated in medulla and cerebral cortex.
starches (-amylase, lingual lipase)
 The muscles are supplied by mandibular division of V cranial nerve

1
 05-04-2023

Swallowing (deglutination) I. ORAL STAGE OR FIRST STAGE- food moves from mouth to pharynx
Deglutition
 Oral stage of deglutition is a voluntary stage.
Three stages
 In this stage, the bolus from mouth passes into pharynx by means of series of
• Voluntary/Oral - initiates swallowing process actions.

• Pharyngeal - passage of food through pharynx into esophagus  Bolus is placed over postero-dorsal surface of the tongue.

• Esophageal - passage of food from pharnyx to  Anterior part of tongue is depressed and Posterior part of tongue is
stomach elevated and retracted against the hard palate.

 Forceful contraction of tongue against the palate produces a positive

pressure in the posterior part of oral cavity.

 This pushes the food into pharynx

II. PHARAYNGEAL – STAGE: - A reflex process

 Center: Swallowing center in located in the floor of IVth ventricle,

 Passage of food from pharynx into oesophagus.
near the respiratory centre at the level of medulla.

 It is a reflex process.
 Efferent: Motor fibers of 5th , 9th , 10th & 12th cranial nerves

 As the bolus touches the pharyngeal wall, it initiates the swallowing or

This initiates the involuntary pharyngeal stage, which includes the closely
deglutition reflex.
co-ordinated movements in the pharynx that pushes the bolus in to the

 Receptors: Stretch receptors in the anterior and posterior pillars of fauces oesophagus, last only for 1-2 sec.

and tonsils, posterior pharyngeal wall, soft palate and epiglottis

 Stimulus: Presence of bolus

 Afferent: Sensory fibers of trigeminal, vagal & glossopharyngeal (V, IX &

X cranial nerves)

Swallowing mechanism.

2
 05-04-2023

Sequence of events in deglutition reflex

 Persistent elevation of the tongue maintains the high pressure gradient. This  Superior pharyngeal constrictor muscle contracts to produces a rapid
prevents the entry of bolus again into the oral cavity peristaltic wave (primary peristaltic wave) that propels the food
downwards (into esophagus)
 Elevation of soft palate closes the nasopharynx and prevents the reflux of
food into nasal cavities  All the above events are the protective mechanisms during second
stage of deglutition
 The vocal cords of the larynx are closely approximated & epiglottis close the
glottis (opening of larynx). Both the above events prevent the entry of food  The respiration stops for a while - ‘Deglutition – apnea’
into the larynx

 Larynx is pulled upwards & forwards, this stretches the opening of esophagus

 Upper esophageal sphincter relaxes and allows the food to pass into
esophagus.

III. OESO PHAGE AL – STAGE

 The passage of food from pharynx to stomach through esophagus is the

third phase of swallowing.

 Upper esophageal sphincter relaxes allowing the food from pharynx into
esophagus

 Three types of peristaltic waves are seen in the body of esophagus.

1. Primary peristaltic wave – continuation of the peristaltic wave produced in

the pharynx by superior constrictor muscle.

 It takes 8-10 secs. to carry food to the stomach.

 But in upright position - food passes to stomach, earlier; in 5-8

secs - due to added effect of gravity.

2. Secondary peristaltic wave – When Primary peristalsis fails to carry all

food to stomach – Secondary Peristaltic wave is initiated by the
distension of esophagus by retained food.

 These waves are produced – due to intrinsic nerve plexuses, present

in the wall, & party due to vagal reflex.

 These waves continue till all the food is emptied into the stomach.

3. Tertiary peristaltic wave – occurs irregularly & locally in the esophagus

 Lower esophageal sphincter relaxes & allows the food to pass into the
stomach

3
 05-04-2023

Applied aspects

1. In lesions of medulla, anaesthesia of pharynx with the cocaine,

deglutition reflex is abolished. Causes regurgitation of food in to the
nose or aspiration of food in to the larynx.

2. CVA (stroke)/cranial nerves damage

1. Aspiration - UES and pharyngeal contractions are not coordinated
2. Secondary peristalsis is still functional

3. Muscular diseases - myasthenia gravis, polio, botulism

4. Anesthesia - aspiration of stomach contents.

Applied – Disorders of swallowing

1. Achalasia

2. Gastroesophageal Reflux Diseases – GERD/Heart bur n

3. Dysphagia

Achalasia Cardia:- Failure of lower esophageal sphincter (LES) to relax. So

food is not emptied into the stomach GERD/ heart burn – Reflux of gastric contents into the esophagus due to
failure of closure of LES. Also called as hiatus hernia.
Cause: Degeneration of the myenteric plexus in the lower part of the
esophagus Features: Heart burn – due to regurgitation of acid containing meals into the
lower part of esophagus. Chest pain, feeling of lump in the throat are other
Features: Dilation of esophagus due to accumulation of the food – called as
features.
megaesophagus
Treatment: Antacids, H2 – blockers, Proton pump blockers
Treatment

1. Antispasmodic drugs to relax – to relax LES

2. Botulinium toxin – to inhibit the release of acetylcholine and

relaxation of LES
Dysphagia - Difficulty in swallowing due to disorders in any stage
3. Surgery – to open the LES

4
 05-04-2023

Slow Waves - Caused by Undulating Changes in Resting Membrane Potential.

Electrical Activity of Gastrointestinal Smooth Muscle
 Most gastrointestinal contractions occur rhythmically, and this rhythm
 The smooth muscle of the gastrointestinal tract is excited by almost
is determined mainly by the frequency of so called “slow waves” of
continual slow, intrinsic electrical activity along the membranes of
smooth muscle membrane potential.
the muscle fibers.
 These waves are not action potentials. Instead, they are slow, undulating
 This activity has two basic types of electrical waves:
changes in the resting membrane potential.
(1) slow waves
 Their intensity usually varies between 5 and 15 millivolts, and their
(2) spikes
frequency ranges from 3 to 12/min, 3 in the body of the stomach, as
 In addition, the voltage of the RMP of the gastrointestinal smooth much as 12 in the duodenum, and about 8 or 9 in the terminal ileum.
muscle can change to different levels, which can also have important
 Therefore, the rhythm of contraction of the body of the stomach,
effects in controlling motor activity of the gastrointestinal tract.
duodenum, & ileum is about 3/min, 12/min, & 8 to 9/ min, respectively.

 The precise cause of te slow waves is not completely understood

 Althougfl they appear to be caused by complex interactions among the

smooth muscle cells & specialized cells, called the interstitial cells of Cajal,
which are believed to act as electrical pacemakers for smooth muscle cells.

 These interstitial cells form a network with each other and are interposed
between the smooth muscle layers, with synaptic like contacts to smooth
muscle cells.

 The interstitial cells of Cajal undergo cyclic changes in membrane potential

due to unique ion channels that periodically open and produce inward
(pacemaker) currents that may generate slow wave activity.

 The slow waves usually do not by themselves cause muscle contraction in

most parts of the gastrointestinal tract, except perhaps in the stomach.

Spike Potentials.

 The spike potentials are true action potentials.

 They occur automatically when the resting membrane potential of the

gastrointestinal smooth muscle becomes more positive than about −40
mv

 The normal resting membrane potential in the smooth muscle fibers of

the gut is between −50 and −60 millivolts.

 Each time the peaks of the slow waves temporarily become more
positive than −40 millivolts, spike potentials appear on these peaks.

 The higher the slow wave potential rises, the greater the frequency of
the spike potentials, usually ranging between 1 and 10 spikes/sec.

5
 05-04-2023

 The channels responsible for the action potentials allow large numbers of
calcium ions to enter along with smaller numbers of sodium ions and
therefore are called calcium-sodium channels.

 These channels are much slower to open and close than are the rapid
sodium channels of large nerve fibers.

 The slowness of opening and closing of the calcium-sodium channels

accounts for the long duration of the action potentials.

 Also, the movement of large amounts of calcium ions to the interior of the
muscle fiber during the action potential plays a special role in causing the
intestinal muscle fibers to contract.

Factors that depolarize the membrane- that is, make it more excitable are
Changes in Voltage of the Resting Membrane Potential.

1. Stretching of the muscle

 In addition to the slow waves and spike potentials, the baseline voltage
level of the smooth muscle resting membrane potential can also change. 2. Stimulation by acetylcholine released from parasympathetic nerve endings

 Under normal conditions, the resting membrane potential averages about 3. Stimulation by several specific gastrointestinal hormones.
−56 millivolts, but multiple factors can change this level.
 Important factors that make the membrane potential more negative, that
 When the potential becomes less negative, which is called depolarization hyperpolarize the membrane & make muscle fibers less excitable are
of the membrane, the muscle fibers become more excitable.
(1) The effect of norepinephrine or epinephrine on the fiber membrane
 When the potential becomes more negative, which is called
(2) Stimulation of the sympathetic nerves that secrete mainly norepinephrine at
hyperpolarization, the fibers become less excitable.
their endings

GI MOTILITY

DR. KHALEEL AHMED MANIK MBBS, MD

PROFESSOR OF PHYSIOLOGY,
IIMSR, INTEGRAL UNIVERSITY, LUCKNOW.

6
 05-04-2023

MOVEMENTS OF SMALL INTESTINE

The movements of small intestine are essential for mixing the chyme with
digestive juices, propulsion of food and absorption.

Types of Movements :

1. Mixing movements :

a) Segmentation movements

b) Pendular movements

2. Propulsive movements

a) Peristaltic movements

b) Peristaltic rush

3. Peristalsis in fasting – Migrating motor complex

4. Movements of villi

7
 05-04-2023

1. Mixing movements :

a) Segmentation movements

b) Pendular movements

2. Propulsive movements

a) Peristaltic movements

b) Peristaltic rush

MIXING MOVEMENTS
Segmentation
a) Segmentation Contractions ( Common, rhythmic segmentation contractions)

 Common type of movements of small intestine, which occur regularly or

irregularly but in a rhythmic fashion are also called rhythmic segmentation  Commonest
 Alternating
contractions.
contraction
 The segment of the intestine involved in each contraction is about 1 to 5cm  Mixing

long. The segments of intestine in between the contracted segments are relaxed.  Resembling the
chain of sausages.
 The length of the relaxed segments is same as that of the contracted segments.

 Both contracted and relaxed segments give a ring like appearance resembling
the chain of sausages.

8
 05-04-2023

 After sometime, the contracted segments are relaxed and the relaxed segments are
contracted.

 Therefore, the segmentation contractions chop the chyme many times. This
helps in mixing of chyme with digestive juices.

Movement Appropriate point

Segmentation movements Occur regularly or irregularly but in a

rhythmic fashion - Alternating
contraction & relaxation

b) Pendular Movement (Small constrictive waves)

 Small constrictive waves sweep forward and backward or

upward and downward and the intestinal loops move like the
pendulum of the clock and, this movement is called the
pendular movement.

 These side to side swaying movements of intestinal loops are

accompanied by lengthening & shortening of intestine. Causes
to and fro movement of the intestinal contents

b) Pendular Movement (Small constrictive waves)

Movement Appropriate point

Small constrictive waves sweep forward and backward
Segmentation movements Occur regularly or irregularly but in a
rhythmic fashion - Alternating
The intestinal loops move like the pendulum of the clock (pendular contraction & relaxation
movement) Pendular movements Small constrictive waves sweep
forward and backward making
intestinal loops move like the
These intestinal loops are accompanied by lengthening & shortening pendulum
of intestine.

This causes to and fro movement of the intestinal contents

9
 05-04-2023

PROPULSIVE MOVEMENTS

 Thus, the chyme requires several hours to travel from duodenum to the
The movements of small intestine involved in pushing the chyme towards the
end of small intestine.
aboral end of intestine are called propulsive movements.

 It travels from point of stimulation in both directions. But under normal

a) Peristaltic Movements
conditions, the progress of contraction in an oral direction is inhibited

 Peristalsis is defined as the wave of contraction followed by wave of quickly and the contractions disappear.

relaxation, which travels aborally at a velocity of 1 to 2cm/sec.

 Only the contraction that travels in an aboral direction persists.

 The contractions are always weak and usually disappear after travelling for  This is because of Starling law of intestine, which is Studied by Bayliss
about few cm distance. & Starling.

 Because of this, the average movement of chyme through small intestine is

very slow, and the average velocity of movement of the chyme is <1cm/sec.

Starling law of intestine/Gut

 According to this law of intestine, the response of the intestine for a local
stimulus consists of a contraction of smooth muscle above(proximally) and
relaxation below(distally) the stimulated area.

 So, the peristaltic contractions start at any part of the intestine travel towards
anal(aboral) end. It dies out in oral direction.

 Reasons

 Frequency of BER(Slow waves) decreases from duodenum to ileum

 Receptive relaxation occurs only distally

 Proof : Resection & re-suturing of a segment of small intestine in reverse

direction - stops peristalsis.

Mechanism:
Presence of food in GI tract Movement Appropriate point
↓
Stretching of GI wall Segmentation movements Occur regularly or irregularly but in a
↓ rhythmic fashion - Alternating
Local myenteric plexus contraction & relaxation
↓ ↓
Pendular movements Small constrictive waves sweep
Ach NO , VIP
forward and backward making
↓ ↓
intestinal loops move like the
Contraction Relaxation
pendulum
Peristaltic movements Wave of contraction followed by wave
of relaxation which travels aborally

10
 05-04-2023

Peristalsis
Factors influencing peristalsis (Neural, Hormonal)

 Function
1. After meals – increases
 Rapid propulsion
of intestinal
2. vagal stimulation – increases
content
 ‘clearing’
3. Sympathetic stimulation – decreases

4. Injury of GI tract – decreases

5. Gastrin & CCK – increases

Segmentation

 Commonest
 Alternating
contraction
 Mixing
 Resembling the
chain of sausages.

b) Peristaltic rush
Movement Appropriate point
 Sometimes, the small intestine shows a powerful peristaltic Segmentation movements Occur regularly or irregularly but in a
contraction. rhythmic fashion

 By excessive irritation or extreme distention of the intestine. Pendular movements Small constrictive waves sweep
forward and backward making
 Begins in duodenum and passes through entire length of samll intestinal loops move like the
pendulum
intestine and finally reaches the ileocecal valve within few
minutes. Peristaltic movements Wave of contraction followed by wave
of relaxation which travels aborally
 The peristaltic rush sweeps the contents of small intestine into
large intestine & relieves the small intestine off of either irritants Peristaltic rush Powerful peristaltic contraction, passes
through entire length of small intestine
or excessive distention

11
 05-04-2023

PERISTALSIS IN FASTING-MIGRATING MOTOR COMPLEX

 This is a type of peristaltic contraction, which occurs in stomach

Significance of Peristalsis in Fasting
and small intestine during the long periods of fasting or several
hours after the meals. 1. Migrating motor complex sweeps the excess digestive
secretions into the colon
 It is different from the regular peristalsis because, a large portion
of stomach or intestine is involved in the contraction. 2. It prevents the accumulation of the secretions in stomach
and intestine.
 It sweeps the excessive digestive secretion into the colon and
prevents the accumulation of the secretions in stomach and 3. It also sweeps the residual indigested materials into
intestine. colon.
 It takes about few minutes to reach the colon after taking origin
from the stomach.

MOVEMENTS OF VILLI
Movement Appropriate point
 During the movement of small intestine, there are
Segmentation movements Occur regularly or irregularly but in a
rhythmic fashion - Alternating simultaneous movements of villi also.
contraction & relaxation
Pendular movements Small constrictive waves sweep  This is because the smooth muscle fibers of the intestinal wall
forward and backward making intestinal extend into the villi also.
loops move like the pendulum
Peristaltic movements Wave of contraction followed by wave  The movements of villi are shortening and elongation, occur
of relaxation which travels aborally
alternatively.
Peristaltic rush Powerful peristaltic contraction, passes
through entire length of small intestine
 The surface area of villi is increased during elongation.
Migrating motor complex Peristaltic contraction, occurs in
stomach & small intestine during
 This helps absorption of digested food particles from the
fasting & travel entire length of small
intestine lumen of intestine.

Match the following Movement Appropriate point

1. Powerful peristaltic contraction, passes Segmentation movements Occur regularly or irregularly but in a
a) Segmentation through entire length of small intestine rhythmic fashion - Alternating
movements contraction & relaxation
1. Wave of contraction followed by wave
Pendular movements Small constrictive waves sweep
b) Pendular movements of relaxation which travels aborally
forward and backward making intestinal
c) Peristaltic movements 2. Occur regularly or irregularly but in a loops move like the pendulum
rhythmic fashion - Alternating Peristaltic movements Wave of contraction followed by wave
d) Peristaltic rush contraction & relaxation of relaxation which travels aborally
e) Migrating motor 3. Small constrictive waves sweep forward Peristaltic rush Powerful peristaltic contraction, passes
and backward making intestinal loops through entire length of small intestine
complex
move like the pendulum Migrating motor complex Peristaltic contraction, occurs in
f) Movements of villi stomach & small intestine during
4. Peristaltic contraction, occurs in fasting & travel entire length of small
stomach & small intestine during fasting intestine
& travel entire length of small intestine

12
 05-04-2023

Regulation of intestinal motility

 Coordinated & regulated by – local , neural & hormonal mechanisms

 Segmental & pendular movements – myogenic , occurs in denervated

loop.

 Peristalsis depend on activity of myenteric plexus

Extrinsic influence & regulation

 Parasympathetic -Vagus – increases – tone & intestinal motility
 Sympathetic – inhibits

 Humoral factors - Motility & Tone

Increased by Decreased by
 Acetylcholine Noradrenalin
 Serotonin Secretin
 Motilin Glucagon
 CCK VIP
 Gastrin NO
 Insulin

 Histamine

 Substance P

13
 05-04-2023

Movements of large intestine

4. Pendular type of movement – peristalsis cum anti peristalsis
 Similar to small intestine
causing mixing of colonic content
1. Segmentation contraction – present in proximal region of
colon (i.e, ascending & transverse region) 5. Peristalsis – wave of contraction sweeping down LI, Frequency less
than SI
2. Haustral contractions or churning in which colonic wall
roll back over the content

3. Kneading movements - alternate contraction & relaxation of

large segments of colon

 Mass movement or mass peristalsis Applied aspect

 1-3 times/day  Constipation: commonest disorder of large bowel motility
 Forceful contractions
 Cause :
 Involve contraction of large segment of colon  Irregular bowel habits
 Propel contents into rectum & induce desire for defecation  Hypothyroidism
 Mass movement can occur after meal  Anal strictures
 Gastro colic reflex  Colon cancer
Mediated by ANS
 Duodeno colic reflex  Diarrhoea: increase in frequency of passage of stools, due to large bowel
irritation
 Cause:
 Infection
 Emotional tension (psychogenic diarrhoea)

181

Colon Motility Disorders

 Adynamic or Paralytic ileus : trauma to intestine cause • Hirschsprung disease (megacolon) - 1/5000
inhibition of smooth muscle - Cause Ganglion cells absent from segment of colon.
 Hirschsprung`s disease or aganglionic megacolon : congenital - Result VIP levels low  SM constriction / loss of
absence of both myentric & submucous plexus coordinated movement  colon contents accumulate (colon
equivalent of achalasia).

- Cure Surgical resection of colon segment lacking ganglia.

182

14
 05-04-2023

DEFECATION

Absorption and storage function

R L

Definition

 Voiding of feces is known as defecation.  The usual stimulus is intake of liquid like coffee or tea or water.

 Feces is formed in the large intestine and stored in sigmoid colon.  Defecation is preceded by voluntary efforts like assuming an
appropriate posture, voluntary relaxation of external sphincter.
 By the influence of an appropriate stimulus, it is expelled out through the
anus.  Compression of abdominal contents by voluntary contraction of
abdominal muscles.
 This is prevented by tonic constriction of anal sphincters in the absence of
the stimulus.  Usually, the rectum is empty.

Defecation reflex  During the development of mass movement, the feces is pushed
into rectum and the defecation reflex is initiated.
 In the sigmoid colon the feces is stored. The desire for defecation occurs
when some feces enters rectum due to the mass movement.  The processes of defecation involves the contraction of rectum and
relaxation of internal and external anal sphincters.
 Desire for defecation is elicited by an increase in the intrarectal pressure to
about 20 to 25cm H2O.

15
 05-04-2023

Pathway

I.Stimulus – distention of rectum

II.Afferent – parasympathetic

III.Center – S2, S3, S4

IV.Efferent – sympathetic – inferior hypogastric plexus

•parasympathetic – nerve of erigenti (S2, S3, S4)

•spinal – pudendal nerve (S2, S3, S4)

V.Result – voiding of feces

16