Transcript Part II Gastric Motility

III GASTRIC MOTILITY
1
Major Function of Gastric Motility
To serve as a reservoir
To break food into small particles and
mix food with gastric secretions
 To empty gastric contents into the
duodenum at a controlled rate
2
1. Anatomy and innervation of the
Stomach
3
4
The stomach can be divided into
three anatomic regions (A)
and two functional regions (B)
A
B
Fundus
Pylorus
Antrum
Corpus
Gastric pump
Phasic contractions
Gastric reservoir
Tonic contractions
5
Functional Anatomy of Stomach
Fundus
Body
Antrum
• Storage
•
•
•
•
•
Oesophagus
Lower Oesophageal
Sphincter
Storage
Duodenum
Pylorus
Mucus
HCl
Pepsinogen
Intrinsic factor
• Mixing/Grinding
• Gastrin
Fundus
Body
Antrum
6
Anatomy
7
Innervation of the GI tract
8
2. Responses to Gastric Filling –
Receptive Relaxation
9
Receptive relaxation
During chewing and swallowing food,
the stimulation of food to the receptors
in mouth, pharynx, and esophagus
reflexly causes the smooth muscle of the
fundus and body of the stomach to relax,
This process allows the stomach to
accommodate a large amounts of food
and fluid.
10
11
The relaxation of the gastric reservoir is mainly regulated
by reflexes.
Three kinds of relaxation can be differentiated:
the receptive, adaptive and feedback-relaxation
Mechanical
stimuli in the
pharynx
1. Receptive
relaxation
3. Feedback
relaxation
2. Adap
relax
Vagus
centre
tive
ation
Tension
receptors
ACH
NO + VIP et al.
CCK
Nutrients
Inhibitory
vagal fibre
(NANC-inhibition)
Nutrients
Relaxation of
gastric reservoir
Distension
12
3. Peristalsis of the Gut and Gastric
Emptying
13
Gastric Motility
Peristaltic waves: Body  Antrum
Body
Thin muscle  weak contraction
 No mixing
Antrum
Thick muscle  powerful contraction
A Mixing
B Contraction of pyloric sphincter 
1 Only small quantity of gastric
content (chyme) entering duodenum
2 Further mixing as antral contents
forced back towards body
14
15
What produces gastric peristaltic waves?
• Peristaltic rhythm (~3/min) generated by pacemaker
cells (longitudinal muscle layer)
• Slow waves – spontaneous depolarisation/
repolarisation
• Slow wave rhythm = basic electrical rhythm (BER)
• Slow waves conducted through gap junctions along
longitudinal muscle layer
• Slow wave depolarisation sub-threshold - require
further depolarisation to induce action potentials 
contraction
• Number of APs/wave determines strength of
16
Gastric Slow Waves and Motility
17
peristalsis
18
Peristalsis
19
Figure 24.4
The contraction of the gastric pump can be differentiated into
three phases:
A: phase of propulsion,
B: phase of emptying,
C: phase of retropulsion and grinding
Phase of propulsion
Phase of emptying
Phase of retropulsion
Antrum
Bulge
Rapid flow of liquids with
suspended small particles
and delayed flow of large
particles towards pylorus
Emptying of liquids with
small particles whereas
large particles are retained
in the buldge of the terminal
antrum
Retropulsion of large
particles and clearing
of the terminal antrum
20
21
Control of gastric motility
Vagovagal reflex – fundal relaxation
Myenteric plexus – slow waves –
contraction
Parasympathetic and Gastrin – increase
contraction force and frequency
Sympathetic – decrease contraction
force and frequency
22
Gastric emptying
1. Def.
The process by which the chyme is expelled from the
stomach into the duodenum is called the gastric emptying.
2. Control
1) stomach: stimulating factor, neuronal and hormonal
2) duodenum: inhibiting factor
entero-gastric reflex, hormones
23
Control of Gastric emptying
Stimulating factors in stomach
Presence of food
Gastrin
24
Control of gastric emptying
25
Balance between gastric
reservoir and antral pump
Gastro-gastric reflexes
Enhanced and
prolonged relaxation of
reservoir
Inhibitory reflex
Distension
Distension
Antral pump switched on
and intensified
Excitatory reflex
26
Control of Gastric emptying
Inhibitory effects in duodenum and jejunum – throug
refelxes and hormones
Inhibitory reflexes – direct – myenteric plexus
indirect – via extrinsic nerves
Neural reflexes stimulated by:
Distension, irritation, acidity, high osmolarity, protein/fat
Fats and acids also stimulate release of humoral factors which
reduce gastric emptying
Cholecystokinin (CCK), stimulated by fats
Secretin, stimulated by acids
27
Enterogastric Reflex
regulates the rate at which chyme leaves the stomach
28
The feedback regulation of gastric emptying is performed
by entero-gastric reflexes and release of intestinal hormones
Vagal
center
Nutrients
Long chain fatty acids
Amino acids
Dipeptids
Glucose
Osmolality
Hydrochloric acid
+
_
+
Inhibitory
vagal fibers
Stimulating cholinergic
vagal fibers
ACH
NO, VIP et al.
CCK
ACH
Reduced opening
of pyloric sphincter
Enhanced
relaxation
and
storage
Backflow
Reduced
contraction
It causes enhanced relaxation of the gastric reservoir, inhibition of the antral
pump, and reduced opening of the pyloric sphincter.
Ehrlein
29 14
Figure
“Quality” of food regulates gastric emtying
non-digestible spheres
30
Solids and liquids of the gastric chyme are emptied with
different velocities.
Lag phase
100
Solids
80
Viscous
content
60
40
Liquid
content
20
0
0
20
40
60
80
100 120
Time (min)
Emptying of liquids is exponential.
Emptying of large solid particles only begins after sufficient grinding
(lag phase).
31
Afterwards the viscous chyme is mainly emptied in a linear fashion
4. Vomiting
• Emesis
• Stretching, toxins, alcohol, spicy foods, and drugs
may stimulate this.
• Emetic Center of the Medulla
• Diaphragm and abdominal wall contract
• Cardiac sphincter relaxes.
• Soft palate rises
32