Description of motility function of GI Tract

1. Movements of Gastrointestinal
Tract

2. Learning Objectives
At the end of this session, the students would be able to:
• List the types of GIT Movements
• Explain mechanism of Mastication & Function
• List the phase of deglutition and explain the mechanism of
deglutition. Explain Achalasia
• List the motor functions of the stomach
• Explain the mechanism of gastric emptying and its regulation
• Describe the types of movements of small intestine and large
intestine
• Explain the mechanism of defecation
• Explain the common gastrointestinal motility disorders

3. Movements of GIT
• Function of Myenteric plexus but alters by extrinsic nervous system
• Mainly Two types of Movements
– Propulsive movement: push chyme toward aboral end
– Mixing Movements: chopping of chyme and mixing chyme with
digestive juices and secretion as well as also facilitate absorption.
• Main movements in GIT are
– Mastication
– Swallowing
– Esophageal Peristalsis
– Gastric Emptying
– Peristalsis
– Haustration
– Defecation reflex

4. Propulsive movements
• Mainly function of myenteric plexus
• Oral to anal, inherent feature of unitary smooth muscle, also called
peristalsis, some degree of mixing as well.
• Characterized by constricting ring on oral side of food bolus and dilating
ring toward anal side
• occur in any part of small intestine and move at a velocity of 0.2-2cm/sec.
They usually dies off after travel this distance.
• new peristalsis state and move a chyme in forward direction, thus several
peristaltic waves occur one after the other and push the small intestine
contents at the distal end of the small intestine
• slow movement of peristalsis waves usually 3-5hours are required for
passage of chyme from pyrolysis to the ileocecal valve.
• segmental and peristalsis movements occurs simultaneously.

5. Mixing movements
• Also called as segmentation movements, controlled by the Myenteric
plexuses
• Allow the chopping of chyme & mixing of enzymes with chyme and
appropriate absorption
• localized constrictor rings appear simultaneously at multiple segments [1-
2 cm] of GIT followed by dilatation of constrictor segment.
• Next few seconds dilated parts constricts and constrictor part dilates.
• Contraction of segment last for 5-6sec, they occur through out the
digestive period
• This type of movements continues
• Such movements are predominant in stomach, duodenum, jejunum, and
ileum.

6. Mastication
• Initially Voluntary later converts as involuntary
• Presence of a bolus of food in the mouth at first initiates reflex
inhibition of the muscles of mastication,
• Drop of lower jaw which initiates a stretch reflex of the jaw muscles-
results in rebound contraction.
• Rebound contraction automatically raises the jaw to cause closure
of the teeth and compresses the bolus again against the linings of
the mouth and inhibits the jaw muscles once again,
• Allowing the jaw to drop and rebound another time; this is repeated
again and again.

7. Mastication Reflex
Presence of a
bolus of food
in the mouth
Voluntary closure
of the teeth & jaw
increases pressure in
mouth compresses the
bolus again against the
linings of the mouth
reflex inhibition of the
muscles of mastication
Drop of lower jaw which
initiates a stretch reflex
causes reflex contraction of
the jaw muscles
reflex contraction of the jaw
muscles to cause closure of the
teeth and compresses the bolus
again
Drop of lower jaw
again

8. Deglutition [Swallowing]
• Refers to passage of bolus from the esophagus to stomach.
• Pharynx complexed the process [being common passage for
respiration & food passage].
• Divided into 3 stages:
1. Oral Phase (voluntary)
2. Pharyngeal phase (involuntary)
3. Esophageal phase (involuntary)
• Initiated voluntarily, sequentially programmed reflex
• Swallowing center located in the medulla
• Receptors in the pharyngeal wall

9. Deglutition reflex
• Receptors: Pressure receptors on the pharyngeal wall,
especially on the tonsillar pillars
• Afferents: V, IX, X cranial nerves
• Center: Medulla oblongata (deglutition centre)
• Efferent: V, IX, X , XII nerves
• Effectors: Muscles of tongue, pharynx, larynx

10. Oral phase
• Begins with contractions of the tongue
and striated muscles of mastication-
forms bolus
• Bolus positioned in the middle of the
tongue and squeezed or rolled
posteriorly into the pharynx by pressure
of the tongue upward and backward
against the palate- trigger the
pharyngeal phase.
• The oral preparatory phase-processing
of the bolus to render it swallowable.
• The oral propulsive phase - propelling of
food into the oropharynx.

11. Pharyngeal phase
• Shortest phase of deglutition, but is the
most complex.
• Involuntary and totally reflexive,
• Lasts approximately 1-2 second
• Involves the receptor areas around the
opening of the pharynx, especially on the
tonsillar pillars,
• Impulses from these pass via from cranial
nerves V, IX (glossopharyngeal) , X (vagus)
and XII [hypoglossal] to the brain stem to
initiate a series of automatic pharyngeal
muscle contractions .

12. a) Elevation of the soft palate: closes posterior nasal
openings, thus preventing food reflux into the nasal
cavities.
b) Elevation of the larynx against the epiglottis: closes
the superior laryngeal orifice (glottis), thus preventing
food entrance into the trachea.
c) Approximation of the vocal cords: This also closes
the glottis, but its role is much more important than that
of the epiglottis.
d) Temporary apnea: stoppage of breathing for few
seconds which also prevents food entrance into the
trachea.
Pharyngeal phase of swallowing

14. Events in Pharyngeal Phase
• Soft palate closes the posterior nares, to prevent reflux of food into
the nasal cavities.
• Tonsillar muscle [palatopharyngeal folds] approximate and make a slit
to prevent passage of big bolus in to posterior pharynx.
• Vocal cords strongly approximated, and larynx is pulled upwards &
anterior by the neck muscles- cause the epiglottis to swing backwards
– Closes the trachea to prevent entry of food into trachea.
– Enlarges relaxes and open upper esophageal sphincter
[pharyngoesophageal sphincter]
• Pharynx begins primary peristaltic wave in the superior part and
spreads downward, propels the bolus into the esophagus.

15. Events in Esophageal Phase
• Primary peristalsis:
– Continuation of the peristaltic wave begins
in the pharynx
– Passes from the pharynx to the stomach in
about 8 to 10 seconds.
– Gravity facilitate movement of food during
upright position
• Secondary peristaltic waves
– Caused due to distention of the esophagus
by the retained food [initiated by myenteric
plexus and partly by reflexes]
• Receptive relaxation of stomach due to wave of
relaxation initiated by myenteric inhibitory
neurons [VIP], precedes the esophageal
peristaltic wave approaching the stomach

16. Disorders of swallowing
• Paralysis of muscle of swallowing or muscle dystrophy- disrupt the
ingestion of food- e.g. Myasthenia gravis
• Drug [Anesthetics] induced inhibition of swallowing reflex- may
results in to aspiration of vomitus- cause asphyxia [Fatal some time]
• Achalasia –
– neurological failure within myenteric plexus-prevent relaxation of
lower esophageal sphincter results in to dysphasia.
– Bolus remain in esophagus casing local distention

17. Motor Function of Stomach
• Storage: large quantities of food until the food can be
processed in the stomach, duodenum, and lower intestinal
tract
• Mixing: food with gastric secretions until it forms a semifluid
mixture called chyme
• Emptying of the chyme: from the stomach into the small
intestine at a rate suitable for proper digestion and
absorption by the small intestine.

18. Stomach
• 3 divisions [fundus, body and antrum with differences in motility], but
divided into two regions,
• Orad region:
– thin walled region, comprises of fundus and the proximal portion of
the body
– Generate much weak contractions and mainly mixing movement
• Caudad region:
– thick walled, contains the distal portion of the body and the antrum
– Generate much stronger contractions than the orad region. Mix the
food and propel into the small intestine.
• Innervation of the stomach includes vagus nerve and sympathetic fibers
originating in the celiac ganglion

19. Divisions of Stomach

20. Storage Function
• Entry of food bolus in stomach results stretch, Activate a "vasovagal
reflex” afferent and efferent of the reflex are carried in the vagus nerve
• Sensory impulse of distention of the stomach sent to the CNS via vagus.
• CNS then sends motor signals to the smooth muscle of the orad
stomach release VIP from these postganglionic vagal nerve.
• Reduces the tone in the muscular wall of the body of the stomach
and causing it to relax. [Receptive relaxation]
• Wall bulges progressively outward, accommodating greater and greater
quantities of food up to a limit, called accommodative relaxation
• Completely relaxed stomach can store up to 0.8 to 1.5 liters of food.

21. Mixing and Propulsion function
• Distention of stomach, initiated by the slow wave
of gut wall -produce a weak peristaltic constrictor
waves, called mixing movement
• Begins in the mid to upper portions of stomach
wall move toward the antrum about 3-4/ seconds.
• As the constrictor waves progress from the body
of the stomach into the antrum, becomes more
intense,
• Digs deeply into the food contents in the antrum
and mix the gastric contents with juice
• These contractions periodically expelled a few
milliliters of antral contents into the duodenum

22. • Most of the antral contents are squeezed back
toward the body of the stomach for further mixing
and further reduction of particle size, called
"retropulsion,”
• Process continues until the food broken down in
very small size and mixing complete.
• Vagus, gastrin and motilin increase the frequency of
action potentials and the force of gastric
contractions.
• Sympathetic stimulation secretin and GIP,CCK
decrease the frequency of action potentials and the
force of contractions.
Mixing and Propulsion function

23. Hunger Contractions
• Refer to special type of intense rhythmical
peristaltic contractions occurs in the body of the
stomach.
• Lasts for 2 to 3 minutes, often fuse to cause a
continuing tetanic contraction
• Most intense in young, healthy people or
during hypoglycemia
• Hunger contraction associated with pain is
called hunger pangs.
• Begin 12 to 24 hours after the last ingestion of
food or 3 to 4 days after starvation, and
gradually weaken in succeeding days.

24. Gastric Emptying
• Propulsion of gastric content into duodenum -Gastric emptying
• Intense mixing movement as tight ring like constrictions begin in mid
stomach and spreading through the caudad stomach called strong
peristaltic contraction
• Each contraction create 50 to 70 cm of water pressure in stomach,
six times as powerful as the usual mixing type of peristaltic waves.
• Higher gastric pressure due intense contraction wave, several
millimeter gastric chyme is propelled in to duodenum by each strong
peristaltic contraction under normal pressure- Cause stomach
emptying.
• As emptying progresses, constrictions rings begin farther and farther
up the body of the stomach, gradually pinching off the food in the
body of the stomach and adding to the chyme in the antrum.

25. Gastric Emptying

26. Regulation of Gastric Emptying
• Control mechanism is mainly Neural and Hormonal, influencing
stomach and duodenal mechanisms
• Stomach Mechanisms : Weaker regulation, promotes emptying
– Volume of food- increase volume food elicit local myenteric reflexes in
the wall that greatly increase activity
– Vagal stimulation- more release of Ach – more force of contraction
– Gastrin: increases antral contraction but increases constriction of
pyloric sphincter – though stimulate force of contraction but decreases
gastric emptying
– Sympathetic postganglionic fibers stimulation decreases gastric
emptying

27. • Duodenal factors: powerful control,
inhibit emptying
• Enterogastric Reflex: Over Distention
of duodenum- inhibit gastric emptying
by reducing gastric peristaltic
contraction and increase pyloric
pump tone.
• More acidic Chyme- inhibit
• Hyperosmotic or hypo-osmotic chyme
– inhibit [maintain fluid balance]
• Protein and fat excess in Chyme –
slows down the gastric emptying
Regulation of Gastric Emptying

28. • Hormonal mechanism:
• cholecystokinin (CCK) released from “I” cells of the mucosa of
the jejunum in response to fatty substances in the chyme. This
hormone acts as an inhibitor to block increased stomach motility
caused by gastrin.
• Secretin is released mainly from “S” cells of the duodenal mucosa in
response to gastric acid passed from the stomach through the
pylorus.
• gastric inhibitory peptide [GIP] is released from the upper small
intestine in response mainly to fat in the chyme, has weak effect of
decreasing gastrointestinal motility.
Regulation of Gastric Emptying

29. Movement of small intestine
• Small intestine comprises of three parts: Duodenum -5%, Jejunum-
40%, Ileum-55%
• Major function- digestion and absorption, propulsion and mixing
movement
• Movement is due to muscular externa – longitudinal and circular
muscle
• Types of Movements
1. Peristalsis (Propulsive)
2. Segmentation contraction (Mixing)
3. Tonic contractions
4. Movements caused by muscularis mucosa and muscle fibers of
villi

30. Segmentation Movements
• Also called as mixing movements
• Ring like contractions , appear at regular
intervals along the gut, then disappear
and then replaced by another set of ring
contractions in the segments between the
previous contractions.
• Determined by slow electrical waves of
BER
• Normally 12/min at duodenum & jejunum,
weakens as moves down (9/min at ileum)
• If excitatory activity of enteric nervous
system is blocked by atropine
contractions become too weak.

31. Functions of segmentation contraction
• Helps in progressive mixing of chyme
with intestinal secretions, ensure
completion of digestion.
• Slow contractions permits longer
contact of the chyme with mucosal
surface and permits absorption
• Influenced with ANS and Hormonal
control
• CCK, Motilin, Gastrin, Ach,
serotonin- increase the motility
• Secretin and glucagon inhibit the
motility

32. Tonic contractions
• Slow and sustained contraction of large segments of
intestine, relatively for prolonged period so isolates one
segment of the intestine with other.
Function same as segmentation.

33. Peristaltic rushes
• Intense peristaltic waves not seen normally ,
• Observed during
– intestinal obstructions,
– intense irritation of mucosa or
– severe cases of infectious diarrhea.
Function : being powerful strong peristalsis, traveling long
distances, sweeps the contents of ileum into colon and
relieves ileum of irritative chyme & excessive distension

34. Migrating Motor Complex
• A propulsive movement initiated during interdigestive phase or
fasting
• begins in the stomach and moves undigested material from the
stomach and small intestine into the colon.
• Movement terminated at the distal ileum and begins a new one in the
stomach.
• Repeats every 90–120 minutes
• High circulating levels of motilin [hormone of the small intestine]
known to cause this movement.
• Function: sweeps the GIT tract having left over undigested food and
prevents the backflow of bacteria from the colon into the ileum

35. Movements of Large intestine
• Function of Proximal half of colon is absorption and distal
half storage & excretion of fecal matter
• Most slow movement,
• Migratory Motor Complex is absent
• Main types of Movements
– Segmentation contraction (Haustrations)
– Mass action contraction or mass peristalsis (unique to colon)
– Defecation

36. Haustration
• Similar to segmentation movements
• Comprises of large circular constrictions with simultaneous contraction
of longitudinal muscle of the colon, cause the unstimulated portion of
the large intestine to bulge outward into baglike sacs called
haustrations.
• Each haustration reaches peak intensity in about 30 seconds and then
disappears during the next 60 seconds.
• Function:
– Facilitate absorption of water converts chyme in to semi solid
– Provide a minor amount of forward propulsion of the colonic
contents.

37. Mass Peristalsis
• Modified type of peristalsis
• Simultaneous contraction of the smooth muscle over the large areas,
occurs twice a day.
• A ring of constriction appears at distended portion extend to 20 or
more centimeters of colon, travels down to colon, sweeping the
descending colon, pushing the feces into rectum.
• Function- moves material from one portion of the colon to other.
• Also move the material into rectum, rectal distension in turn initiates
defecation reflex.

38. Defecation reflex
• Stimulus- distension of the rectum with feces, following a mass
peristalsis.
• Normally defecation is a spinal level reflex, but to some extent
voluntarily can be controlled.
• Reflex consists of development of peristaltic waves in the sigmoid
colon & rectum pushing the feces into anus, increased pressure in
anus, relaxation of internal anal sphincter.
Steps of defecation
• Mass movement
• Filling of rectum
• Desire of defecation
• Stimulate intrinsic myenteric reflex

39. Defecation reflex
• External sphincter: skeletal muscle, voluntary control
• Internal sphincter: ring of smooth muscle, involuntary control
• distension of the rectum with feces, following a mass peristalsis –
caused by myenteric reflex ,
• Mass peristalsis in the terminal colon fills the rectum and causes a
reflex relaxation of the internal anal sphincter and a reflex contraction of
the external anal sphincter.
• Voluntary relaxation of the external sphincter accompanied with
propulsive contraction of the distal colon complete defecation.
• Conscious desire control the anal sphincter by exciting or inhibiting
pudendal nerve- results in defecation

40. Defecation reflex
• In adults habits & cultural factors play
a large role in determining when
defecation occurs.
• By voluntary efforts help reflex in
emptying of distended rectum. Such
as
• Violent expiratory efforts with glottis
closed ,
• Raises intra abdominal pressure,

41. Hirschspurng's disease or megacolon
• Rare congenital disorder, caused by absence of nerve
cells [Ganglion cells deficiency in the myentric plexus]
in the rectum and/or colon.
• Severe constipation, bowel movements may occur only
once a week or so, leads to accumulation of large
quantities of fecal matter,
• Colon may distend to a diameter of 3-4 inches.

42. Irritable bowel syndrome
• Group of symptoms that occur together.
• Symptoms include
• abdominal pain or cramping, bloating, gas,
• Altered bowel movement patterns such as diarrhea or constipation
Abdominal or stomach cramping and pain that are relieved with
bowel movements
• Number of theory to describe pathophysiology proposed
• Result from a combination of abnormal gastrointestinal tract
movements, a disruption in the communication between the brain
and the gastrointestinal tract movements

43. Disorders of motility of large intestine
Constipation:
• Infrequent bowel movements (less than 3 per
week), passage of hard stools, and sometimes
difficulty in passing stool.
Diarrhea:
• An excessive number of high amplitude
propagating contractions. Symptoms are frequent,
loose or watery stools