2. Outlines of Lecture
• Introduction of Alimentary tract
• Functions of GIT
• Histology of Gut
• Electrical Activity of GI smooth muscle
• Neural control of GI function
• Hormonal control of GI motility.
11. GI smooth muscle
•Smooth muscle fibres are electrically connected
through GAP JUNCTIONS
• That allow ions to move from one cell to next.
•Each muscle layer functions as SYNCYTIUM
• When an action potential is elicited in muscle
mass, it generally travels in all directions.
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12. GI smooth muscle.
Unitary (single unit) smooth Muscle.
• The fibers usually are arranged in sheets or
bundles, their membranes are adherent at
multiple points, these are gap junctions. This
also known as syncytial smooth muscle or
visceral smooth muscle
• e.g. Gut. Bile duct. Ureters, Uterus and blood
vessels.
13. Electrical activity of GI
Smooth Muscle
• Resting MP of GI smooth muscle is about-
56 mv.
• Slow Waves
» These are slow undulating changes in
resting MP of GI smooth muscle.
» They are not true AP, but they control
Spike potentials.
» Duration is 5-15 msec
» Caused by pumping activity of Na-K
pump.
14. Electrical activity of GI
Smooth Muscle
• Spike Potentials
» These are true action potentials that
occur when RMP of GI smooth muscle
rises above-40 mv.
» Caused by slow Ca-Na pump
» Duration is 10-20 ms.
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17. Neural Control of GI Functions
(Autonomic NS)
» Parasympathetic NS
» Cranial PS innervation by vagus
nerve
» Esophagus
» Stomach
» Small Intestine
» Pancreas
» 1st half of Large Intestine
18. Neural Control of GI Functions
(Autonomic NS)
• Parasympathetic NS
» Sacral PS innervation by pelvic
nerves
» For distal half of colon
• Sympathetic NS innervates all portions of
GIT.
19. Difference between the myenteric and sub mucosal
plexuses
Myenteric Plexus Submucosal(Meissner’s) Plexus
It lies between longitudinal and circular
layers of intestinal smooth muscle.
Functions.
A) Excitatory.
• increased tonic contractions
• Increased intensity of rhythmical
contractions.
• Slightly increased rate of rhythm of
contraction.
• Increased velocity.
B) Inhibitory
Inhibit intestinal sphincter muscles to
impede movement of food
• Pyloric sphincter
• Lower oesophageal sphincter
• Sphincter of the ileocecal valve
It is located in the sub mucosa.
Functions.
• Sensory signals originate from
the gastrointestinal epithelium
and integrated in this plexus to
help control.
1. Local Intestinal secretions
2. Local absorption
3. Local contraction of the sub
mucosal muscle that causes
various degrees of infolding of
gastrointestinal mucosa.
20. Neurotransmitters secreted by
enteric neurons.
1. Acetylcholine
2. Nor epinephrine
3. Serotonin
4. Dopamine
5. Cholecystokinin
6. Substance – P
7. Vasoactive intestinal polypeptide
8. Somatostatin
9. Leu – enkephalin
10. Met - enkephalin
11. Bombesin.
21.
22. Gastrointestinal reflexes
► The anatomical arrangement of enteric nervous system
and its connections with sympathetic and
parasympathetic system
► Three types of Reflexes
1. Reflexes that are integrated entirely within the gut wall
enteric nervous system.
1. Control GI Secretions, peristalsis, mixing
contractions, and local inhibitory effects.
23. Gastrointestinal reflexes
1. Reflexes from the gut to the pre vertebral
sympathetic ganglia and then back to the
gastrointestinal tract.
I. Gastro colic reflex.(signals from the
stomach to cause evacuation of the colon)
II.Enterogastric reflex (signals from the
colon and small intestine to inhibit
stomach motility and stomach secretion )
III.Coloileal reflex(colon to inhibit emptying
of ileal contents into the colon)
2.Reflexes from the gut to the spinal cord or
brain stem and then back to
gastrointestinal tract.
24. I. Pain reflexes (pain reflexes that
cause general inhibition of the entire
gastrointestinal tract)
II.Defecation reflex (reflexes that
travel from the colon and rectum to
the spinal cord and back again to
produce the powerful colonic, rectal,
and abdominal contractions required
for defecation)
III. Vagovagal reflex (reflexes from
the stomach and duodenum to the
brain stem and back to the
stomach—by way of the vagus
nerves— to control gastric motor and
secretary activity)
27. Movement of GIT(Functional)
• Two types
1. Mixing movements
• Caused by
• Peristaltic contractions
• Local constrictive contractions.
2. Propulsive movements
• Caused by
• Peristalsis
28. Movement of GIT(Functional)
• Peristalsis
• It is contractile ring that appears in syncytial
smooth muscle tubes.
• It causes any material in front of it to move
forward.
• Caused by Myenteric plexus.
• Law of GUT
• Myenteric reflex plus analward direction of
movement of peristalsis.
32. Splanchnic Circulation
• Splanchnic Circulation includes blood flow through
• Gut
• Spleen
• Pancreas &
• Liver.
• Almost all of the FATS absorbed from intestinal
tract are carried by intestinal lymphatics & then to
Thoracic duct
• Bypassing the Liver
36. Control of GI Blood flow
• Two types of control
• Local Control
• Increased Gut activity leads to increased
blood flow towards Gut.
• Mediated by local vasodilators like CCK,
VIP, Gastrin, Secretin, & Bradykinin.
• Decreased O2 concentration also
causes local vasodilation
37. Control of GI Blood flow
• Neural control
• Parasympathetic NS
• Increases GI blood flow due to
increased GIT activity.
• Sympathetic NS
• Decreases GI blood flow due to
vasoconstriction of arterioles.
38. Autoregulatory Escape
• After sympathetic vasocontriction, local
metabolic vasodilator mechanisms initiated
due to ischemia, cause re vasodilation of
GIT blood vessels.
39. Countercurrent blood flow
mechanism in villi
• Arterial flow into and venous flow out of villus
are in opposite directions & lie close to each
other, so that O2 & other nutrients can
diffuse easily.
• In normal conditions this is not harmful
• But in condition like Circulatory Shock, O2
deficit in tip of villus is too much that it causes
Ischemic death of tip or even whole villus.
