lec 4 Flashcards
Anatomically the stomach is composed of
the fundus, body and the antrum.
Physiologically the stomach composed of
The orad portion or Gastric Reservoir part (tonic contraction):
2. the caudad portion or Antral pump (phasic contraction):
the caudad portion or Antral pump (phasic contraction):
lower third of the body & antrum
The orad portion or Gastric Reservoir part (tonic contraction)
fundus & upper two thirds of the body
The smooth muscle layers in the fundus and body are
thin
The smooth muscle layers in the antrum
has much heavier musculature
Control of gastric motility
- Vago-vagal reflex
- Parasympathetic and Gastrin
- Sympathetic
Vago-vagal reflex
fundal relaxation
Parasympathetic and Gastrin:
increase contraction force and frequency
Sympathetic
decrease contraction force and frequency
Function of Gastric Motility
- reservoir
- break food into small particles and mix food with gastric secretions
- empty gastric contents into the duodenum
volume when the stomach empty
50 ml;, 1 L ,1.5 L
The stomach AND V during meal
a 20-fold change in volume
The stomach AND tension during meal
little change in tension
The stomach AND intra-gastric pressure, during meal
little rise in intra-gastric pressure
cause of little change in tension and
little rise in intra-gastric pressure
deep folds of stomach
During a meal
the folds get smaller and nearly flatten out
the stomach relaxes slightly with each mouthful
three kinds of gastric relaxation difference
is the region and the receptors
Types of Receptors of gastric relaxation
- receptive relaxation
- adaptive relaxation
- feedback-relaxation
receptive relaxation
swallowing of food (before stomach )
adaptive relaxation
food in stomach →stretch receptors
feedback-relaxation
food in duodenum →the release of CCK
stretch receptors
mechano or tension receptors)in stomach
;givegus
Afferent: vagus
c. Center: vagal center
d. Efferent: vagus ►enteric neurons (inhibitoryneurotransmitter: Nitric oxide or VIP)
e. Effector organ: muscle relaxation of stomach wall
vagal innervation is interrupted
↑ intra-gastric pressure →vomiting
vomiting result from
the inability of the proximal stomach smooth muscle to undergo receptive relaxation.
the newest food lying closest to
the esophageal opening
the oldest food lying nearest the
the outer wall of the stomach
functions of gastric reservoir
to store
to evacuate digesta
The emptying of the reservoir is caused by two mechanisms:
by a tonic contraction of the reservoir and
by peristaltic waves moving
As food enters the stomach, it forms
the food in the orad portion of the stomach
Both the peristaltic waves and the tonic
contractions of the reservoir are stimulated
by cholinergic & enteric neurons
cholinergic & enteric neurons are
under modulatory
vagal tone
In the region of the gastric corpus the
peristaltic waves only produce
a small circular constriction → mix superficial layer
in the center of the gastric reservoir
the pH remains high and the digestion of starch by amylase continues
Mechanical contraction of stomach
Electrical activity of gastric wall
Mixing movement:
Peristaltic activity, manifested as
slow waves occurs at the basal electrical rate (BER) of the stomach (3-4 waves/minute)
Slow waves conducted through
gap junctions along longitudinal muscle layer
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in the mid-portion of the greater curvature (the
proximal corpus), and travel distally towards the pylorus
once every 15 to 20 seconds
Propagating is slightly faster velocity along the greater
curve than along the lesser curve.
The gastric action potential lasts about
5 seconds
four phases of A,P IN GI
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Phase 0
Resting membrane potential; outward potassium current.
Phase 1
Rising phase (upstroke depolarization); activation of voltage-gated calcium channels and voltage-gated potassium channels.
Phase 3
Plateau phase; balance of inward calcium current and outward potassium current
Phase 4
Falling phase (repolarization); inactivation of voltage-gated calcium channels and activation of calcium-gated potassium channel
Mixing movement includes
- Peristaltic movements
2. Retropulsion movements
The mechanical peristaltic movements caused by
depolarizing spikes at peak of basal electrical rhythm cycle
peristaltic contraction increases by
Gastric distension ↓ vagal stimulation ↓ release of acetylcholine ↓ increase of gastrin ↓ ↑contraction
Peristaltic contraction begins in
the mid stomach and proceed caudally.
As the wave proceeds towards the pylorus it become
deeper,
stronger and
faster (
in pylorus traveling
3-4 cm/sec
in fundus
(< 1 cm/sec) .
n the deep wave of contraction
at proximal third of antrum away from pylorus:
pylorus is relaxed
peristalsis may push antral content (water and small food particles) toward the duodenum
Pylorus thickness of the circular wall muscle becomes
50 to 100 percent
greater than in the earlier portions of the stomach antrum
the pyloric circular muscle is called
the pyloric sphincter.
why the pyloric circular muscle is called the pyloric sphincter.
Pylorus remains slightly tonically contracted almost all the time
solids food fate
- reduced to between 1-2mm in size before delivered to the duodenum.
- large, indigestible solids remain in the stomach
Retropulsion movements
sievingغربلة function
antral systole)
peristaltic waves are most marked in distal half of stomach
Liquids pass through the pylorus in
spurtsدفقات
In the fasting condition the pyloric sphincter remains
relaxed
When food enters the pyloric sphincter re
closes
The time of opening the sphincter depends on:
a) The normal motility of the stomach,
(b) Quality and consistency of the food
(c) Stage of digestion
with water and liquid diet, the sphincter
opens
a mixed diet the sphincter opening starts
15 minutes (average half an hour)
The degree of constriction of the pylorus is increased or decreased under the influence of
nervous signals
hormonal signals
from both the stomach and the duodenum
Some evidence suggests that it is controlled by opiates, acetylcholine, and nitric oxide (NO)
retropulsion
The backward movement of food particles
mixing movement beneficial effects are
to effectively mix food and gastric secretions,
to grind gastric contents into chyme.
Gastric emptying is
the chyme is expelled from the stomach into the duodenum
Gastric emptying results from a
progressive wave of forceful contraction
Gastric emptying involves
antrum
pyloric sphincter
proximal duodenum
Gastric emptying is determined by the force of
gastric peristalsis and NOT the variation in tone of pyloric sphincter
Gastric emptying waves
spread over the antrum as strong peristaltic ring-like contraction
Gastric emptying waves
50-70cmH2O
Gastric emptying occurs when the chyme is decomposed into
enough small pieces
(typically <1 mm2) to fit through pyloric sphincter.
Significance of gastric emptying:
1.prevents solid and bigger food particles from entering التحكم ب حجم حبات الطعام duodenum
2.allows small volume (2-7mL) of chyme from entering التحكم ب حجم سائل الطعام.time a at duodenum
3.prevents
التحكم ب عدم رجوع الطعامstomach in chyme of regurgitation
The contraction of the pyloric (or gastric or antral ) pump phases
phase of propulsion
phase of emptying
phase of retropulsion and grinding
phase of retropulsion and grinding
terminal antrum
Jet-like back-flow with grinding +
duodenal contraction
Retropulsion of large particles and clearing
of the terminal antrum
Due to the regularly occurring pacesetter
potentials these phases occur cyclically.
phase of propulsion
Contraction of proximal antrum Propulsion of chyme into terminal antrum +
Duodenal contraction
Raid flow of liquids with suspended small particles and
Delayed flow of large particles towards pylorus
phase of emptying
Contraction of middle antrum Transpyloric and retrograde flow +
duodenal relaxation
Emptying of liquids with small particles whereas
large particles are retained in the bulge of the terminal antrum
