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

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 IRRITATION OF GASTRIC MUCOSA EXCESSIVE DISTENTION OF THE GUT 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 PROPULSIVE MOVEMENTS 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