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Gastrointestinal physiology II.
Motility of the GI tract
Learning objectives: 67, 69, 70, 75.
prof. Gyula Sáry
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Bayliss studied the heart, circulation and the
gastrointestinal tract.
Together with Starling they discovered
secretin, the first endocrine substance in
1902 and thus founded modern
endocrinology.
Bayliss made some fundamental
observations concerning peristaltic activity in
the gut.
Sir William Maddock
Bayliss
1860-1924
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serosa
longitudinal muscles
circular muscles
submucosal layer
mucosa
mesenterium
(arteries, veins, nerves, lymph vessels)
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Boron, Boulpaep, Medical Physiology,
Elsevier Saunders, 2012
2
Types of smooth muscles
Electrical activity of GI smoot muscle
- muscle cells connected via gap junctions
- the resting potential is less negative (than sceletal muscle cells) and oscillates
- mesenchymal pacemaker cells (interstitial cells of Cajal)
• BER: Basic Electrical Rhythm
(slow waves) triggered
by pacemaker cells
and propagated
by smooth muscle.
Resting
ACh
Stretch
Noradrenaline
• Spikes = action potentials
superimposed on slow waves.
Spikes are associated with
Ca++ influx.
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Motor activity of GI smooth muscle
•
•
•
Only APs elicit contractions
The frequency of contractions depend on the slow waves
The force of contractions depend on the number of spikes
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How slow
waves are
generated
Boron, Boulpaep, Medical Physiology,
Elsevier Saunders, 2012
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4
Pacmaker activity of GI smoot muscle
I
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Sanders et al. NIPS, Dec. 2000
slow waves in cultured cells
slow waves in the gut (jejunum)
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Migrating motor complexes (MMC)
•
•
•
Electrical and motor activity occurring during fasting.
Activity lasts for 3-5 min and recurs at 90-100 min periods.
Activity starts in the stomach and moves aborally.
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Migrating motor complexes (MMC)
•
•
•
Electrical and motor activity occurring during fasting.
Activity lasts for 3-5 min and recurs at 90-100 min periods.
Activity starts in the stomach and moves aborally.
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Movement types in the GI tract
•
Tonic contraction with intermittent relaxation: sphincters
•
Segmentation
•
Peristalsis
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Segmentation
Segmental contractions are responsible for mixing
There is no netto forward movement
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The law of the gut (BAYLISS)
Stimulation in the GI tract elicits gut movements
1. Contraction on the oral
side of the stimulation, and
2. ..relaxation on the
caudal (aboral) side, and
Stimulation
3. ..the contractile ring preceded by
dilatation moves in aboral direction.
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IPAN= Intrinsic Primary Afferent Neuron
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Exners’s phenomenon
Needle thrown
into the wall causes
stimulation.
Sharp (pointed)
objects turn
in the GI tract.
Peristalsis
Peristalsis turns
the needle.
Peristalsis pulls
out needle.
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Motor functions of the GI system: the mouth
Food intake:
Sucking (brainstem reflex in the newborn)
Biting
CHEWING (MASTICATION)
Chewing deficit does not compromise digestion but the process is greatly
prolonged and large particles may hurt gastric mucosa.
Chewing is a unilateral reflex:
• Opening the mouth activates a stretch reflex and the jaw rises.
• Stimulation of mechanoreceptors in the mucosa inhibits
stretch reflex and the jaw drops.
• Opening the mouth activates a stretch reflex and the jaw rises.
etc.
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SWALLOWING (DEGLUTITION)
1. From the mouth to the pharynx.....voluntary phase
2. Pharyngeal stage
.....................reflex phases
3. Esophageal stage
}
• All passages that are normally open must be closed (airways).
• The passage that is normally closed (esophagus) must open.
• The peristaltic wave starts from the pharynx.
• Muscles of the pharynx and upper third of the esophagus are striated muscle:
peristaltic activity in the upper portion of the alimentary canal is controlled by
somatomotor innervation.
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SWALLOWING (DEGLUTITION)
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ESOPHAGUS
Primary peristalsis:
Peristaltic wave initiated
from the pharynx.
upper esophageal sphync.
Secondary peristalsis:
residual bolus left in the
esophagus initiates new
peristalsis.
(e.g., during vomiting)
lower esophageal sphync.
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PRESSURE WAVES IN THE ESOPHAGUS DURING
SWALLOWING (esophagometry)
Boron, Boulpaep, Medicap
Physiology, Elsevier Saunders, 2012
ACHALASIA
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FUNCTIONAL DIVISONS OF THE STOMACH
MOTILITY
SECRETION
Proximal (orad)
portion
Distal (caudad)
portion
Oxyntic (HCl producing)
portion
Gastrin producing
portion
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FUNCTIONS OF THE STOMACH
• Storage and emptying in small portions
• Production of intrinsic factor
• HCl promotes absorption of iron
• Trophic influence on the rest of the GI tract (gastrin)
• Grinding, milling
• Digestion of proteins
• Bacteriostatic function
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MOTILITY OF THE PROXIMAL PORTION OF THE STOMACH
During the filling phase:
• receptive relaxation
• vago-vagal reflex,
• local reflex,
• stress relaxation
After the filling phase:
tonic contraction
The proximal portion does
not participate in peristalsis.
X
stretching
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proximal part
of the stomach
pacemaker
distalis
distal parts
gyomor
of the stomach
t
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Boron, Boulpaep, Medical Physiology,
Elsevier Saunders, 2012
15
MOTILITY OF THE DISTAL PORTION OF THE STOMACH
1. During fasting: MMC
2. Filled state: PERISTALSIS
pacemaker
region
• The major function of the stomach is storage and grinding.
• The pyloric region contracts before the peristaltic wave reaches the pylorus.
• The pyloric canal serves as a „filter” allowing only small parts to pass
• Only 2-4 ml liquid chyme enters the duodenum.
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contraction ring
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CONTROL OF GASTRIC EMPTYING
Intestinal mechanisms:
INHIBIT EMPTYING
Humoral:
CCK
Secretin
GIP
Gastric mechanisms:
PROMOTE EMPTYING
Protein
Lipid
Acid
Neural:
Hyperosmosis
Acid
Distention
Neurotensin
Ileum
Distention
Protein
Gastrin
pyloric sphincter:
intrinsic neurons (enkephalin, VIP)
extrinsic: vagus, sympathicus
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Boron, Boulpaep, Medical Physiology,
Elsevier Saunders, 2012
17
FUNCTIONS OF THE SMALL INTESTINE
• Digestion
• Mixing
• Absorption of food degradation products
• Absorption of water and electrolytes
• Absorption of vitamins
• Transport
• Immunological protection
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MOTILITY OF THE SMALL INTESTINE
1. MMC (in fasting condition)
2. Segmentation
3. Peristalsis - slow peristalsis (short segments)
- peristaltic rush (irritation, long distance)
REFLEXES
1. Gastroenteric reflex
2. Intestino-intestinal reflex
Gastrin:
stimulation of
motility
Pain
Sympathetic
inhibition
of motility
(paralytic ileus)
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14th century illustration of vomiting
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VOMITUS
cerebellum
Evoking stimuli:
Gastric irritants peritonitis
mechanoreceptors
chemoreceptors
pain
chemosensitive trigger zone
(Area postrema)
medullary center
Kinetosis
Drugs
psychic, emotional stim.
pregnancy
irradiation
…
Nausea: symptoms preceding
vomitus
• Contractions in the small intestines
and in the stomach
• Müller maneuver
• Relaxation of the LES
• Contraction of the abdominal muscles
• Relaxation of UES
• Closure of the airways
• Forceful expiration (Valsalva)
• Vomitus
Reverse filling of the stomach is caused by giant
retrograde intestinal contractions
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FUNCTIONS OF LARGE INTESTINE
• Moderate capacity to absorption of water and electrolytes
• Transport
• Storage and controlled evacuation
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REGULATION OF THE ILEOCECAL JUNCTION
Gastroileal reflex
Filling of
the ileum
Filling or
irritation
of the colon
Ileocecal sphincter
Gastrin:
relaxation
of sphincter
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MOTILITY OF THE COLON
Haustral shuttling
~ segmentation
Mass movement
~ peristalsis
Gastro-colic
reflex
Gastrin:
increased
motility
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Boron, Boulpaep, Medical Physiology,
Elsevier Saunders, 2012
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MOTILITY OF THE RECTUM AND ANAL CANAL: DEFECATION
sacral
spinal cord
sympath.
ggl.
n. pelvicus
(parasympathetic)
• Parasympathetic
reflex elicited by
distention of the
rectum (1 & 2).
• External anal
sphincter is
controlled
voluntarily (3).
n. pudendus
(somatomotor)
α2
m. sphincter
ani ext.
m. sphincter
ani int.
Passive and active
incontinentia
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Fear realted unrination defecation
Cortex, pons, amygdala
sacral
spinal cord
sympath.
ggl.
n. pelvicus
(parasympathetic)
• External anal
sphincter is
controlled
voluntarily (3).
n. pudendus
(somatomotor)
α2
m. sphincter
ani ext.
• Parasympathetic
reflex elicited by
distention of the
rectum (1 & 2).
m. sphincter
ani int.
Passive and active
incontinentia
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