The enteric nervous system controls gastrointestinal movements and secretions. It is composed of two plexuses: the myenteric plexus between the longitudinal and circular muscle layers, which controls gastrointestinal movements, and the submucosal plexus beneath the mucosa, which controls secretion and blood flow. The enteric nervous system works with the sympathetic and parasympathetic nervous systems to regulate gastrointestinal function. Sensory neurons in the gut wall send signals to the central nervous system to mediate reflexes. The enteric nervous system contains many types of neurons that secrete neurotransmitters like acetylcholine, serotonin and VIP.

1. ENTERIC NERVOUS SYSTEM
• 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

2. NEURAL CONTROL OF GUT WALL

3. 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

4. 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 POLYPEPTIDE (INHIBITING INTESTINAL SPHINCTER
MUSCLES)
• SUBMUCOSAL PLEXUS: CONTROL FUNCTION OF EACH MINUTE SEGMENT OF
INTESTINE
• LOCAL INTESTINAL SECRETION, LOCAL ABSORPTION, LOCAL CONTRACTION OF
SUBMUCOSAL MUSCLE

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

6. 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

7. 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

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

9. 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

10. 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)

11. HORMONAL CONTROL OF GASTROINTESTINAL MOTILITY
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
CHOLECYSTIKININ
• SECRETED: “I” CELLS IN THE MUCOSA OF THE DUODENUM AND JEJUNUM
• STIMULI: FAT, FATTYACIDS AND MONOGLYCERIDES
• ACTIONS: BILE, INHIBIT STOMACH CONTRACTION AND APPETITE

12. SECRETIN
• SECRETED: “S”CELLS IN THE MUCOSA OF THE DUODENUM
• STIMULI: ACIDIC GASTRIC JUICE
• ACTIONS: GASTROINTESTINAL MOTILITY, PANCREATIC SECRETION OF
BICARBONATE
GASTRIC INHIBITORY PEPTIDE
• SECRETED: MUCOSA OF UPPER SMALL INTESTINE
• STIMULI: FATTY ACIDS, AMINO ACIDS
• ACTIONS: DECREASE STOMACH MOTILITY, INSULIN SECRETION

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

14. 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

15. 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

16. 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

17. 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

18. ARTERIAL BLOOD SUPPLY TO INTESTINE

19. 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

20. 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)

21. “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

22. 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