Download Peristalsis

MOTILITY OF THE GUT
NERVES
PACEMAKER
ACTIVITY
HORMONES
MOTILITY
PACEMAKER OF THE GUT
It is a thin layer of interstitial cells
; interstitial cells of Cajal, lying
between circular and longitudinal
cell layer.
interstitial cells of Cajal
It is characterized by:
a slow wave activity
gap junctions
tight synapses with enteric
nerves
PACEMAKER OF THE GUT
Insert fig. 18.16
Electro-physiology of smooth
muscles of the GUT
Resting membrane potential
It is -50 to - 60 mV with potential
oscillations
Slow Waves = Pacemaker
Potential = Basic Electric Rhythm
(BER)
It is spontaneous rhythmic
fluctuation in the smooth muscles
membrane potential between
– 60 mv & – 40 mv.
It is initiated by the interstitial cells of
Cajal
Pacemaker potential
They are not followed by
muscle contraction unless they
reach a threshold for the spike
potentials.
site
Frequency of BER
Stomach
3/min
Duodenum
12/min
Distal ileum
8/min
Cecum
9/min
Pacemaker zone of the stomach
The action potentials (spike
potentials)
is produced when slow-waves reach
the threshold automatically due to
Opening of L-type calcium channels
This is induced by Stretch of smooth
muscle, vagal stimulation, hormones
or myenteric plexus stimulation.
1- nervous stimulation
2- distension (stretch)
3- hormones
Enteric nervous system (gut brain)
Enteric nervous system (gut brain)
Enteric nervous system (gut brain)
The myenteric plexus has
Sensory receptor neurons
Motor effector neurons
The neurotransmittors
Excitatory & Inhibitory
Functional types of
movements in GIT
Functional types of
movements
Propulsive
movements
(peristalsis)
Mixing
movements
Peristalsis
stretch
vagal
++Enteric neurons
Contractile rings
irritants
Peristalsis
Peristalsis
This signal is transmitted by
interneurons
Excitatory (proximal) motor neuron
Inhibitory (distal) motor neurons,
bolus is transported in oral to
caudal direction
Mixing movement
They are local intermittent
constrictive contractions occur every
few cms in the gut wall, lasts only 5 -
30 seconds then new constrictions
occur at other points keeping the
contents thoroughly mixed together
Mixing movement
Patterns of motility
Tonic contractions
continuous contractions with different
intensity lasts minutes to hours.
It is caused by continuous repetitive
spike potential, any factor causes
continuous partial depolarization, or by
hormones.
It is usually occurs at the
sphincteric regions
Hunger contraction
It is rhythmical continous tetanic
intense prestalsis on empty stomach,
lasts 2-3 minutes in young.
It may cause mild pain in the pit of
stomach, hunger pange especially after
12 hours – 4 days of starvation then it
is gradually weakened.
Receptive relaxation of the
stomach:
When the esophageal peristalsis
approaches the stomach , a wave of
relaxation occurs in the entire stomach
to the duodenum to prepare to receive
food.
It is due to ++ of myentric inhibitory
neurons.
Reverse
peristalsis
(antiperistalsis)
It is peristaltic waves occur in the
reverse direction usually between
stomach and duodenum and
between ileum and cecum
Propulsive peristalsis:
It is the basic movements occurs in
esophagus, lower 2 thirds of
stomach, small and large intestine,
and rectum
Peristaltic rush
irritation of small intestine results
in powerful peristalsis travel the
whole intestine in minutes to
sweep its contents e.g., as on
cases of infectious diarrhea
Haustration (segmentation of the
colon)
it is simultanous strong contraction of
the circular muscles and teniae coli of
the colon results in out plugging of the
distal part to allow dug into and roll over
the fecal material to absorb fluid and
dissolved substances
Mass movements
It is peristalsis in the colon 1-3time/day.
20 cm distal to the constrictive ring
loses haustrations and contract as a
unit to propel the fecal content in mass
then inhibited to be returned after
hours mediated by autonomic fibers.
It appear after meals facilitated by
gastro-colic and ilio-colic reflexes.
Migrating motor complex (MMCs):
It is a fasting long peristalsis every 6090 minutes from the stomach to the
terminal ileum.
It sweeps any undigested food in
preparation for the next meal &
helps to prevents bacteria from
remaining in the small intestine
It is the mechanical processing of food
and made it ready to swallow
Grinding
Mixing é
saliva
Breaking
Softening
it is important for digestion of all foods
•
To increase the total surface area exposed to
the digestive secretions
chewing process is controlled
by nuclei in the brain stem
a chewing reflex
Once/sec

Primary peristalsis
To sweep the oesophagus
8 - 10 sec
 Secondary peristalsis
distention of the esophagus
myenteric circuit & by reflexes
Deglutition (swallowing)
The start is voluntary, but it is
completed reflexly.
The speed of swallowing depends on
the consistency of food.
The voluntary phase:
The pharyngeal phase:
The oesophageal phase:
The voluntary phase:
The pharyngeal phase:
contraction of the constrictor muscles of the
pharynx occurs accompanied by receptive
relaxation of the upper esophageal sphincter.
The pharyngeal phase:
1)
The posterior pillars approximate
to shut off the mouth cavity
2) Protective reflexes:
The oesophageal phase:
It is involuntary, passage of food to
the stomach
is rapid in the upper part & slow in the
lower end
Receptor
Afferent
around the pharyngeal
opening
V, IX, X
deglutition center
Center
Efferents
V, IX, X, XI, XII
motor functions
of stomach
Storage
Mixing
Emptying
Tonic
contraction
Peristalsis
Hunger
contraction
Receptive
relaxation
MMC
Tonic contraction
Maintained mild to moderate contraction
In the fundus
To maintain the I G pressure
The contenets
Receptive
relaxation
With food intake
Seeing,
smellig,
tasting
Bolus in
oesophagus
Bolus in
stomach
Peristalsis
Shortly after food intake
Mixing
Grinding
Propulsion
Peristaltic movement
esophagus
1
pyloric sphincter
2
3
duodenum
Fig. 7.6, p. 124
Hunger contraction
In empty stomach
Strong peristalsis in the body
after 12-24 h of last meal
Reach its max. 3-4 days
Due to hypoglycemia
If very strong
fuse
tetanic contraction
Hunger pain
Migration motor complex
In interdigestive state
Peristalsis starts in the oesophagus
Occurs every 60 – 90 min
Due to motilin
GIT
The
stomach usually
empties completely
within3-4 hours after a
meal.
The rate of gastric
emptying depends on the
contents of the stomach
as well as duodenal
factors
Stomach emptying
Gastric factors Duedenal factors Others
_____
+++++
1- volume of
gastric contents
1- enterogastric
reflex
2- gastrin hormone 2- hormones :
Secretin, CCK
1- chemicals
2- autonomic
Sympathetic
and parasymp.)
3-emotions
4-consistency
GIP, somatostatin &type of food
Intestinal motility
1- peristaltic movements (propulsive)
2- segmenting movements (mixing)
3- antiperistalsis
4- MMC
5- movement of the villi
6- peristaltic rush
1-Segmentation: mix contents to promote
digestion & absorption. It is myogenic i.e.
controlled by the basic electric rhythm (BER).
Mixing contraction of the Small Intestine.
Rhythmic Segmentations Bring Through
Mixing of the Intestinal Content
Intestinal Motility
Peristaltic movement
Stimulus
1-Distension of the duodenum
or the stomach (gastroenteric
reflex)
2- mechanical or physical
irritation
Rate or velocity
Velocity=0.5-2 cm/sec slower
distally, then die out after few
cms
Control
Neurogenic: Local myenteric
reflex (low of the gut)
Segmentation movement
Distension with chyme in the
small intestine
Rate= 11-12 in the duodenum
8-9 in the terminal ileum
Myogenic in nature (slow wave
+ spike potential on top)
Intestinal Motility
Peristaltic movement
Segmentation movement
Description
Circular muscle contraction
proximal to the bolus and
receptive relaxation distal to it,
While the longitudinal muscles
relax proximal to the bolus and
contract distal to it
Ring like contractions dividing
a loop of the intestine into
equal portions. Then, these
contractions relax and a new
set of contractions begin in the
previously relaxed points.
Functions
1-Mixing the contents with
intestinal secretion
2-Increase its exposure to
the brush border
1-Forward movement of food
towards the iliocecal valve
2-Spread out of the chyme
along the intestinal mucosa
Motility of the colon
• Segmental contractions
(corresponds to segmentation in small intestine)
= Haustration
• Peristalsis and antiperistalsis (reverse peristalsis)
• Mass movement
Large intestinal
motility patterns

Segmental contraction
(haustration)

peristalsis
Mass peristalsis
1- gastrocolic reflex
2- duodenocolic reflex
3- gastroilial reflex