Download Motility function of the gastrointestinal system

Motility function of the
gastrointestinal system
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The 3 major patterns of the digestive tract
motility
1. Peristalsis
2. Rhythmic segmentation
3. Tonic contraction
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• Usually the stimulus for peristalsis is distention
• It requires intact enteric nervous system but can
be modulated by the autonomic nervous system
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Esophageal Function
 Esophagus is a collapsible muscular tube.
It transports food to stomach
Secretes mucus with no digestive or absorptive function.
Upper oesophageal
sphincter (UES)
* UES closes in between
swallowing to:
– Prevent esophageal contents
reflux
into pharynx
–Prevents air entry into the
esophagus
Diaphragm
Lower oesophageal
sphincter (LES)
 LES :
–Closed in between swallowing
–Prevents stomach content reflux into
esophagus
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Swallowing or Deglutition
 Swallowing is the movement of food from
mouth into the Stomach
It is facilitated by secretion of saliva and
mucus
It involves mouth, pharynx and esophagus
It is coordinated by the swallowing center in
medulla oblongata and lower pons
It involves 3 phases or stages (oral,
pharyngeal & esophageal)
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Phases of Swallowing
1. Oral phase:
Voluntary
The swallowing
starts when the food
bolus is forced to the
back of the oral
cavity and into the
pharynx by the
movement of the
tongue upward and
backward against
the palate
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Phases of Swallowing
2. Pharyngeal phase (Involuntary)
• Tongue sweeps backward →
bolus into the oro-pharynx
• Elevation of soft palate and
contraction of the upper constrictor
muscle of the pharynx to close
nasopharynx.
• Epiglotis and vocal cords
shut off the larynx
• Reflex apnea
• Relaxation of UES
• Peristatic contraction begins in the
upper constrictor muscle → middle &
inferior constrictor muscle
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Phases of Swallowing
3. Esophageal Phase (Involuntary)
 Begins once the food bolus enters the
esophagus
 Peristalsis pushes the bolus onwards.
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Esophageal Phase cont…

At the lower of the
oesophagus
 LES (Cardiac
sphincter) relaxes
to allow the bolus to
enter the stomach
 It is usually closed
to prevent gastric
reflux
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Functions of the stomach
1. Storage of ingested food until
it is emptied into small
intestine.
2. Secretion of HCl and enzymes
that begin protein digestion.
3. Stomach mixing movements:
─ Ingested food is pulverized and
mixed with gastric secretion 
Chyme
─ Chyme is emptied into the
duodenum (gastric emptying)
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Stomach Motility Function
 Four Aspects of Gastric Motility:
 Gastric Filling
 Gastric Storage
 Gastric Mixing
 Gastric Emptying
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Gastric Filling and storage:
•
The stomach is able to accommodate such a 20-fold change in
its volume
 Question: HOW?
 Answer: Receptive Relaxation
─ During a meal stomach relaxes slightly with each mouthful
RECEPTIVE RELAXATION
─ Receptive relaxation enhances the stomach ability to
accommodate with extra volume of food.
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Gastric emptying & mixing:
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1. Peristaltic contraction (PC)
originates in the upper fundus → the
pyloric sphincter
2. The PC becomes more vigorous as it
reaches the antrum.
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3. The strong PC propels the chyme
forward
4. A small portion of the chyme is
pushed through the “partially” open
sphincter into the duodenum
5. When PC reaches the pyloric
sphincter, the sphincter closes tightly →
No further emptying
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6. The chyme that was not delivered in to
the duodenum is forced backward into the
stomach for further mixing
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Regulation of Gastric emptying
Distension of the stomach by the presence of food
Secretion of gastrin and increase parasympathetic impulses
Stimulate contraction of lower esophageal sphincter,
increase motility of the stomach
Relax of the pyloric sphincter
Gastric
emptying
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Distension of the duodenum by chyme, fatty acids
Enterogastric reflex
parasympathetic stimulation
Sympathetic stimulation
CCK
Gastric motility
Carbohydrates
empty > Proteins >
fats
Inhibition of gastric
emptying
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Small Intestine





Site of digestion and absorption
Divided into 3 regions: duodenum, jejunum,
ileum
Joins the large intestine at ileocecal sphincter
Stomach chyme must be transported from
duodenum down the full length of the small
intestine for digestion and absorption to take
place efficiently.
Chyme is chopped, churned and mixed with
small intestine secretions
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Small intestine Motility
Two types of SI movement
1. Segmentations

Mix contents with the digestive
juices and bring the particles of
food into contact with the
mucosa for absorption

They do not push the intestinal
contents along the tract.
2. Migrating motility complexes
(MMC)

It is type of peristalsis

It starts in the lower stomach
and pushes chyme forward along
the small intestine.

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Ileocecal sphincter
Ileocecal juncture prevents
contamination of the small
intestine by large intestine
contents.
Normally remain partially
closed.
After a meal gastroileal reflex
intensifies ileum peristalsis and
forces chyme into caecum.
Gastrin cause sphincter
relaxation.
When caecum distended the
contraction of ileocaecal
sphincter intensifies
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Large Intestine
Figure 23.29a
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Motility of Large Intestine
1. Haustration (segmentation in colon)
• Slow segmenting movements that move the contents of the
colon (occur every 30 min)
• Controlled by the intrinsic plexuses
• Stimulated by distension
• Movement are slow → absorptive and storage functions
2. Mass movements (propulsive movements)
• ↑↑↑ motility in ascending and transverse colon occurring after a meal
• Drive the colonic contents to the distal portion of large intestine
• Triggered by:
─ Gastrocolic and duodenocolic reflexes
─ Irritation
─ Intense parasympathetic stimulation
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Defecation Reflex
Parasympathetic nerve
Fibers (pelvic nerve)
Two anal sphincters:
 Internal anal
sphincter: smooth
muscle & NOT
under voluntary
control.
 External anal
motor
sphincter: striated Skeletal
nerve (pudendal
nerve)
muscle, under
voluntary control &
is innervated by the
pudendal nerve
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Defecation Reflex
Mass movement
Rectum is distended
Activation of stretch receptors
Signals to sacral spinal cord
Gives desire to defecate
Through pelvic nerve (parasympthatic),
relaxation of internal anal sphincter
If the conditions are
right:
Voluntarily relaxation
of external anal
sphincter allows
defecation.
Otherwise, the reflex
subsides until the
rectum is filled again
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