The enteric nervous system (ENS) is a web of sensory neurons, motor neurons, and interneurons embedded in the wall of the gastrointesinal system, stretching from the lower third of the esophagus right through to the rectum. The neurons of the ENS are arranged in two layers, the submucosal and myenteric plexuses of the gut wall. It has been estimated that the ENS actually contains more neurons than the whole of the spinal cord. The ENS processes a range of sensations, such as the nature of gut contents and gut distension, and integrates this information with input from the autonomic nervous system. In this way the ENS can guide and optimise the muscular and secretory activity of the gastrointestinal tract. Many of the ENS effector neurons are also innervated by parasympathetic motor neurons, so they act as effector neurons of the parasympathetic nervous system. For this reason the ENS is regarded as an integral part of the parasympathetic nervous system, but its specialized sensory neurons and independent processing make it rather more complex than a simple parasympathetic ganglion. The ENS displays sophisticated coordination and exhibits plasticity and learning in response to changing dietary habits or disruptions to the gut.

1. ENTERIC NERVOUS SYSTEM

3. ENS
• LOCATION: WALL OF GUT
• NEURONS: 100 MILLIONS
• GIT MOVEMENTS AND SECRETIONS
• COMPOSED: TWO PLEXUSES
• OUTER PLEXUS (MYENTERIC AND AUERBACH'S PLEXUS)
• INNER PLEXUS (MEISSNER'S PLEXUS AND SUBMUCOSAL PLEXUS)
• MYENTERIC PLEXUS
• GI MOVEMENTS
• SUBMUCOSAL PLEXUS
• SECRETION AND LOCAL BLOOD FLOW

4. NEURAL CONTROL OF GUT WALL

5. EXTRINSIC SYMPATHETIC AND PARASYMPATHETIC FIBERS
MYENTERIC AND SUBMUCOSAL PLEXUS
GASTROINTESTINAL FUNCTION INHIBIT OR ENHANCE
SENSORY NERVE ENDINGS
AFFERENT FIBERS
PREVERTEBRAL GANGLIA
SPINAL CORD
VAGUS NERVES → BRAIN STEM
LOCAL REFLEXES
REFLEXES PREVERTEBRAL GANGLIA OR BASAL REGIONS BRAIN

6. DIFFERENCES B/W MYENTERIC AND
SUBMUCOSAL PLEXUSES
• MYENTERIC PLEXUS: LINEAR CHAIN OF INTERCONNECTING NEURONS
• LONGITUDINAL AND CIRCULAR LAYERS OF INTESTINAL SMOOTH MUSCLE
• CONTROL MUSCLE ACTIVITY ALONG WALL OF GUT
• TONIC CONTRACTION OF GUT WALL, INCREASE INTENSITY AND SLIGHT INCREASE RATE OF
RHYTHMICAL CONTRACTION, INCREASE VELOCITY OF CONDUCTION OF EXCITATORY WAVES
CAUSING MORE RAPID MOVEMENT OF GUT PERISTALTIC WAVES
• VASOACTIVE INTESTINAL POL
YPEPTIDE (INHIBITING INTESTINAL SPHINCTER MUSCLES)
• SUBMUCOSAL PLEXUS: CONTROL FUNCTION OF EACH MINUTE SEGMENT OF
INTESTINE
• LOCAL INTESTINAL SECRETION, LOCAL ABSORPTION, LOCAL CONTRACTION OF
SUBMUCOSAL MUSCLE

7. TYPES NEUROTRANSMITTERS SECRETED BY ENTERIC
NEURONS
• ACETYLCHOLINE
• NOREPINEPHRINE
• ADENOSINE TRIPHOSPHATE
• SEROTONIN
• DOPAMINE
• CHOLECYSTOKININ
• SUBSTANCE P
• VASOACTIVE INTESTINAL POLYPEPTIDE
• SOMATOSTATIN
• LEU-ENKEPHALIN
• MET- ENKEPHALIN
• BOMBESIN

10. AUTONOMIC CONTROL OF GIT PARASYMPATHETIC INNERVATION
• CRANIAL AND SACRAL DIVISIONS
• CRANIAL PARASYMPATHETIC IN VAGUS NERVES
• OESOPHAGUS, STOMACH, PANCREASE AND
LARGE INTESTINE
• SACRAL PARASYMPATHETIC S2, S3, S4 OF THE
SPINAL CORD
• PELVIC NERVES → DISTAL HALF OF LARGE
INTESTINE → ANUS
• POSTGANGLIONIC NEURONS (MYENTERIC AND
SUBMUCOSAL PLEXUSES )
• ENHANCE GI FUNCTIONS

11. SYMPATHETIC INNERVATIONS
• INHIBIT GIT ACTIVITY AND OPPOSITE TO PARASYMPATHETIC SYSTEM
• SPINAL CORD: B/W SEGMENT T-5 and L-2
• PREGANGLIONIC FIBERS, AFTER LEAVING THE CORD, ENTER THE SYMPATHETIC CHAINS,
THEN TO OUTLYING GANGLIA (CELIAC GANGLIA AND VARIOUS MESENTRIC GANGLIA)
• POSTGANGLIONIC SYMPATHETIC NEURON BODIES ARE IN THESE GANGLIA, AND POST
GANGLIONIC FIBERS THEN SPREAD THROUGH POSTGANGLIONIC SYMPATHETIC NERVES
TO ALL PARTS OF THE GUT
• THE SYMPATHETIC INNERVATE ESSENTIALLY ALL OF THE GIT, RATHER THAN BEING MORE
EXTENSIVE NEAREST THE ORAL CAVITY AND ANUS

12. SECRETE:
NOREPINEPHRINE
EPINEPHRINE
EFFECTS:
• INHIBIT INTESTINAL SMOOTH
MUSCLE
• INHIBITORY EFFECT ON
NEURONS OF ENTERIC
NERVOUS SYSTEM
STRONG STIMULATION:
INHIBIT MOTOR MOVEMENT OF
THE GUT

13. AFFERENT SENSORY NERVE FIBERS FROM THE GUT
 STIMULATION OF SENSORY NERVES
1. IRRITATION OF GASTRIC MUCOSA
2. EXCESSIVE DISTENTION OF THE GUT
3. PRESENCE OF SPECIFIC CHEMICAL IN THE GUT
• SENSORY SIGNALS GUT→SPINAL CORD AND BRAIN STEM
• 80 PERCENT NERVE FIBER IN VAGUS ARE AFFERENT
• GUT→BRAIN MEDULLA → VAGAL REFLEX
SIGNALS
 →GASTROINTESTINAL TRACT

14. GASTROINTESTINAL REFLEXES
• GUT WALL ENTERIC NERVOUS SYSTEM (GASTROINTESTINAL
SECRETION, PERISTALSIS, MIXING CONTRACTION,LOCAL INHIBITORY
EFFECT)
• GUT→PREVERTEBRAL SYMPATHETIC GANGLIA→GIT (GASTROCOLIC
REFLEX, ENTEROGASTRIC REFLEXES, COLONOILEAL REFLEX)
• GUT→SPINAL CORD OR BRAIN STEM→GIT(GASTRIC MOTILITY AND
SECRETION, PAIN REFLEXES, DEFECATION REFLEXES)

16. CHOLECYSTIKININ
• SECRETED: “I” CELLS IN THE MUCOSA OF THE DUODENUM AND
JEJUNUM
• STIMULI: FA
T
, FA
TTY
ACIDS AND MONOGL
YCERIDES
• ACTIONS: BILE, INHIBIT STOMACH CONTRACTION AND APPETITE

17. GASTRIN
• SECRETED: “G” CELLS OF ANTRUM OF STOMACH
• STIMULI: MEAL, DISTENTION OF STOMACH, PROTEINS
AND GASTRIN RELEASING PEPTIDE
• ACTIONS: GASTRIC ACID SECRETION, GROWTH OF GASTRIC
MUCOSA

18. SECRETIN
• SECRETED: “S”CELLS IN THE MUCOSA OF THE DUODENUM
• STIMULI: ACIDIC GASTRIC JUICE
• ACTIONS: GASTROINTESTINAL MOTILITY, PANCREATIC SECRETION OF
BICARBONATE

19. GASTRIC INHIBITORY PEPTIDE

SECRETED: MUCOSA OF UPPER SMALL INTESTINE

STIMULI: FATTY ACIDS, AMINO ACIDS
 ACTIONS: DECREASE STOMACH MOTILITY, INSULIN
SECRETION

20. MOTILIN
• SECRETED: STOMACH AND UPPER DUODENUM
• STIMULI: FASTING
• ACTIONS: INCREASE GASTROINTESTINAL MOTILITY, WAVES OF
GASTROINTESTINAL MOTILITY (90 MIN)
• INHIBITED: INGESTION

21. Functional Types of Movements in the Gastrointestinal
Tract
1. PROPULSIVE MOVEMENTS
2. MIXING MOVEMENTS
PROPULSIVE MOVEMENTS (PERISTALSIS)
CONTRACTILE RING
INHERENT PROPERTY OF SYNTIAL SMOOTHI
MUSCLE TUBE
BILE DUCT etc.
• DISTENTION OF GUT
• IRRITATION OF EPITHELIAL LINING IN THE GUT
• STRONG PARASYMPATHETIC NERVOUS SIGNALS
TO GUT

22. FUNCTION OF MYENTERIC PLEXUS IN
PERISTALSIS
• CONGENITAL ABSENCE OF MYENTERIC PLEXUS
• TREATED WITH ATROPINE
DIRECTIONAL MOVEMENT OF PERISTALTIC WAVES TOWARDS THE ANUS
• EITHER DIRECTION
• MYENTERIC PLEXUS POLARIZED IN ANAL DIRECTION

23. RECEPTIVE RELAXATION
• INTESTINAL TRACT: PERISTALSIS BEGINS IN ORAD DIRECTION
• PUSHING INTESTINAL CONTENTS 5-10 CM IN ANAL DIRECTION
• GUT RELAX SEVERAL CM DOWNSTREAM TOWARDS ANUS
MYENTERIC REFLEX OR PERISTALTIC REFLEX
LAW OF THE GUT (PERISTALTIC REFLEX AND ANAL DIRECTION MOVEMENT OF
PERISTALSIS )
MIXING MOVEMENTS
PERISTALTIC CONTRACTION
LOCAL INTERMITTENT CONSTRICTIVE CONTRACTIONS
LAST: 5-30 SEC

24. GASTROINTESTINAL BLOOD FLOW
SPLANCHNIC CIRCULATION
BLOOD FLOW: GUT, SPLEEN, PANCREAS AND LIVER
(LIVER SINUSOIDS)
RETICULOENDOTHELIAL CELLS (REMOVE BACTERIA
AND OTHER PARTICULATE MATTER)
CARBOHYDRATE AND PROTEIN ABSORPTION
FATS ABSORPTION

25. ARTERIALBLOOD SUPPLY TO
INTESTINE

26. ARTERIAL BLOOD SUPPLY TO
GUT
• SUPERIOR MESENTERIC,
• INFERIOR MESENTERIC ARTERIES
• CELIAC ARTERY
ARTERIES BRANCH AND CIRCLING BOTH DIRECTIONS AROUND GUT
MUCH SMALLER ARTERIES PENETRATE INTO INTESTINAL WALL AND ALONG THE
MUSCLE BUNDLE, INTO INTESTINAL VILLI, SUBMUCOSAL VESSELS
BLOOD FLOW THROUGH INTESTINAL VILLUS MULTIPLE LOOPING
CAPILLARIES

27. EFFECT OF METABOLIC FACTORS ON GI BLOOD FLOW
• LEVEL OF LOCAL ACTIVITY
• BLOOD FLOW INCREASES EIGHTFOLD
• AFTER MEAL, MOTOR, SECRETORY, ABSORPTIVE ACTIVITIES INCREASED WITH
INCREASE BLOOD FLOW
CAUSES OF INCREASED BLOOD FLOW DURING GASTROINTESTINAL ACTIVITY
VASODIALATORS SUBSTANCES (PEPTIDE HORMONES) CHOLECYSTOKININ,
VASOACTIVE INTESTINAL PEPTIDE, GASTRIN, SECRETIN
TWO KININS (KALLIDIN, BRADYKININ), POWERFUL VASODIALATORS
DECREASED OXYGEN CONCENTRATION IN GUT WALL (BLOOD FLOW 50-100%)
ADENSOINE (VASODIALATOR)

28. “COUNTERCURRENT” BLOOD FLOW IN THE
VILLI
• ARTERIAL FLOW AND VENOUS FLOW IN OPPOSITE DIRECTIONS AND
CLOSE TO EACH OTHER
• BLOOD OXYGEN DIFFUSES OUT OF THE ARTERIOLES INTO VENULES
• SHORT CIRCUIT ROUTE
• DISEASE CONDITIONS BLOOD FLOW TO GUT LESS
• VILLUS SUFFER ISCHEMIC DEATH
• IN GASTROINTESTINAL DISEASES, DIMINSHED INTESTINAL
ABSORPTIVE CAPACITY

29. NERVOUS CONTROL OF GASTROINTESTINAL BLOOD FLOW
• STIMULATION OF PARASYMPATHETIC NERVES
• SYMPATHETIC STIMULATION DIRECT EFFECT ON ALL GASTROINTESTINAL TRACT CAUSE
VASOCONSTRICTION OF ARTERIOLES WITH DECREASED BLOOD FLOW
• AUTOREGULATORY ESCAPE (LOCAL METABOLIC VASODIALATOR MECHANISM)
IMPORTANCE OF NERVOUS DEPRESSION OF GASTROINTESTINAL BLOOD FLOW
WHEN OTHER PARTS OF BODY NEED EXTRA BLOOD FLOW
SYMPATHETIC VASOCONSTRICTION IN GUT SHUTOFF OF GI AND SPLANCHNIC BLOOD FLOW
• SYMPATHETIC STIMULATION CONSTRICTION OF LARGE VOLUME INTESTINAL AND
MESENTERIC VEINS
• LARGE AMOUNT OF BLOOD IN OTHER PARTS OF CIRCULATION
• IN HEMORRHAGIC SHOCK, 200-400 ml BLOOD