gastro intestinal reflexes


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gastro intestinal reflexes

  1. 1. Addis Ababa University College of Health Sciences Department of Medical Physiology Presentation on Gastro intestinal ReflexesBy Girmay fitiwi 10/30/2011 1
  2. 2. Presentation out Line1.Objectives2.Introduction3.Short reflexes4. Long reflexes 4.1. Defecation reflexes 4.2. Vomition (emesis ) reflexes5. References10/30/2011 gastro intestinal reflexes 2
  3. 3. 1. ObjectivesAt the end of this presentation students willable to :-• Mention the types of gastro intestinal reflexes• Clarify the roles of different GI reflexes• Explain the mechanisms of defecation reflexes• list the control mechanisms of defecation• Discuss the mechanism, merits and demerits of vomiting reflexes.10/30/2011 gastro intestinal reflexes 3
  4. 4. 2. introduction• The digestive system has a complex system of motility and secretion regulation which is vital for proper function.• Accomplished via a system of long reflexes from the CNS, short reflexes from ENS and reflexes from GI peptides working in harmony with each other.• Three types of gastrointestinal reflexes .10/30/2011 gastro intestinal reflexes 4
  5. 5. …………..cont’d1.Local reflexes• Reflexes that are integrated entirely within the gut wall enteric nervous system.• These include reflexes that control much gastrointestinal secretion, peristalsis, mixing contractions, local inhibitory effects.10/30/2011 gastro intestinal reflexes 5
  6. 6. GI reflexes cont’d2. Short reflexes• Reflexes from the gut to the prevertebral sympathetic ganglia and then back to the gastrointestinal tract.• These reflexes transmit signals long distances to other areas of the gastrointestinal tract.• gastrocolic reflex• enterogastric reflex.• colonoileal reflex.• Ileogastric reflex10/30/2011 gastro intestinal reflexes 6
  7. 7. GI reflexes cont’d …………3.Long reflexes• Reflexes from the gut to the spinal cord or brain stem and then back to the gastrointestinal tract. Vago vagal reflexes Pain reflexes that cause general inhibition of the entire gastrointestinal tract. Defecation reflexes Vomition reflexes10/30/2011 gastro intestinal reflexes 7
  8. 8. Different nervous reflexes of the GIT10/30/2011 Fig.1 different gastro intestinal reflexes 8
  9. 9. GI reflex cont’d10/30/2011 Fig.2 reflex control of gut activity 9
  10. 10. Distension of stomach by food Mucous membrane of stomach is stimulated Afferents go to internal plexus Efferents from internal plexus G- cells in pyloric Gastric glands glands Release of gastric juice 10Fig .3 Short reflex
  11. 11. Presence of food in stomach Mucous membrane of stomach is stimulated Afferents go via the vagus Medullary centre Efferents come via vagus Synapse in the intrinsic plexuses G-cells in pyloric Gastric glands glandsFig.4 Long reflex 11 Release of gastric juice
  12. 12. 3.Short Reflexes1. Gastrocolic (Gastroileal) Reflex• Stomach activity leads to ileocecal relaxation and increased mass movements in the colon.• These reflexes are mediated through both long and short nervous pathways (extrinsic and intrinsic) and hormones (CCK, gastrin)  Most evident after first meal of the day.  Often followed by urge to defecate.  New born children routinely defecate after meal.10/30/2011 gastro intestinal reflexes 12
  13. 13. Short reflexes cont’d2.Enterogastric reflex When fat or protein chyme reaches the duodenum, receptors detect and send impulses to enteric nerves of the stomach that in turn cause the inhibition of stomacheal motility and secretion. Delays emptying.3. Intestino-intestinal Distention of one portion of the intestine leads to decreased contractions caudad of the bolus.  Depends on extrinsic neural connections.10/30/2011 gastro intestinal reflexes 13
  14. 14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4 Nerve impulses inhibit peristalsis in stomach wall From CNS Vagus nerve To CNS 1 Duodenum fills with chyme 3 Sensory nerve impulses travel to central 2 Sensory stretch nervous system receptors are10/30/2011 Fig.5 enterogastric reflexes 14 stimulated
  15. 15. Short reflexes cont’d4. Vago vagal reflexes• GI reflex circuits where afferent and efferent fibers of the vagus nerve coordinate responses to gut stimuli via the dorsal vagal complex in the brain.• Controls contraction of the GI muscle layers in response to distension of the tract by food.• Allows for the accommodation of large amounts of food in the GITs.10/30/2011 gastro intestinal reflexes 15
  16. 16. ……….cont’d• Carries signals from stretch receptors, osmoreceptors, and chemoreceptors to dorsal vagal complex where the signal may be further transmitted to autonomic centers in the medulla.• Efferent fibers of the vagus then carry signals to the gastrointestinal tract up to the splenic flexure.10/30/2011 gastro intestinal reflexes 16
  17. 17. ………….cont’dFunction• Active during the receptive relaxation of the stomach in response to swallowing of food .• When food enters the stomach a "vagovagal" reflex goes from the stomach to the brain, and then back again to the stomach causing a reduction in the muscular tone of the stomach wall.10/30/2011 gastro intestinal reflexes 17
  18. 18. …………..cont’dMechanism• when the corpus and fundus of the stomach are distended secondary to the entry of a food bolus.• stimulation of the mechanical receptors located in the gastric mucosa stimulates the vagus afferents.• The completion of the reflex circuit by vagus efferents leads to the stimulation of postganglionic muscarinic nerves.• These nerves release Ach to stimulate two end effects.10/30/2011 gastro intestinal reflexes 18
  19. 19. ……………..cont’d1.The parietal cells in the body of the stomach are stimulated to release H+.2. The ECL cells of the lamina propria of the body of the stomach are stimulated to release histamine.10/30/2011 gastro intestinal reflexes 19
  20. 20. 4. Long reflexes4.1 defecation reflexes• An Intrinsic reflex mediated by the local enteric nervous system in the rectal wall.• To be effective it usually must be fortified by parasympathetic defecation reflex• Distention of the rectum causes the internal anal sphincter to relax, which produces the urge to defecate.• The external anal sphincter is under voluntary control.• relaxation of this sphincter, coupled with contraction of the rectum and sigmoid colon, results in defecation.10/30/2011 gastro intestinal reflexes 20
  21. 21. Defecation reflexes cont’d10/30/2011 Fig 6. anatomical view of rectum and anal channel 21
  22. 22. …………..cont’d• Rectum usually (almost) empty (retrograde contractions return content to sigmoideum, until there is too much of it)• Just before defecation mass movement in sigmoideum fills rectum pressure reflex relaxation of inner sphincter (smooth muscle) & contraction of outer sph. (skeletal muscle controlled intentionally via pudendal nerves)• Stretch receptors in rectal wall can adapt - urge to defecate can temporarily subsided suppressed.10/30/2011 gastro intestinal reflexes 22
  23. 23. Defecation Reflexes cont’dA. Intrinsic reflex• Intrinsic reflex mediated entirely by ENS is initiated when feces enters rectum via mass movements and the rectal pressure increase to 55 mmHg. – Peristaltic waves in descending colon, sigmoid and rectum – Relaxation of internal anal sphincter (inhibitory action of the myenteric plexus) – Weak when functioning alone.10/30/2011 gastro intestinal reflexes 23
  24. 24. 10/30/2011 24 Fig7. defecation reflexes
  25. 25. …………cont’d B.Parasympathetic defecation reflex • Involves sacral segments of the spinal cord . • Greatly intensifies intrinsic reflex (but is not different qualitatively) • Afferent signals go to sacral cord and then back to descending and sigmoid colon, and rectum by way of parasympathetic fibers in pelvic nerves. • The lower neurons S2-S4 provide sensory and motor fibers for defecation reflex.10/30/2011 gastro intestinal reflexes 25
  26. 26. 10/30/2011 gastro intestinal reflexes 26
  27. 27. ………………….cont’d • Afferent signals entering spinal cord initiate other effects that require intact spinal cord.  Deep breath, closure of glottis, and increased abdominal pressure  Relaxation and movement of pelvis floor downward  All work to move fecal contents downward • Spinal transection or injury can make defecation a difficult process. • Cord defecation reflex can be excited (either digitally or with enema) ,Forcing fecal particles into the rectum to cause new reflexes, Not as effective as the natural reflexes.10/30/2011 gastro intestinal reflexes 27
  28. 28. Vomiting (emesis)• The ejection of stomach contents through the mouth.• preceded with nausea, sometimes anorexia, autonomic reactions (salivation, sweating, cold skin,...)• Vomiting center in medulla (next to cardiovascular & respiratory centers).• CTZ located in the root of 4 th ventricle.• Protective reflex against toxicity; however, longer vomiting can cause metabolic alkalosis & dehydration.10/30/2011 gastro intestinal reflexes 28
  29. 29. …………….cont’d  There is a neural connection between vomition center and CTZ.  CTZ causes central vomition and is stimulated by chemical substances (e.g., drugs like morphines , pregnancy, alcohol, movement etc.)10/30/2011 gastro intestinal reflexes 29
  30. 30. Vomiting cont’d• Reverse peristalsis from the middle of small intestine to larynx .• Strong contraction of abdominal muscles&diaphragm.• Relaxation, then closure of pylorus, relaxation of LES and finally UES (glottis closure, inhibition of breathing)• Forced inspiration against closed glottis - intrathoracic pressure, abdominal (diaphragm)10/30/2011 gastro intestinal reflexes 30
  31. 31. …………cont’d• Vomiting may be induced by:-1.Drugs like apomorphine stimulate CTZ.2.Afferent impulses from vestibular nuclei• They mediate vomiting of motion sickness3.Afferent impulses from viscera stimulate vomiting center via NTS.• Vomiting induced in visceral disease.10/30/2011 gastro intestinal reflexes 31
  32. 32. 10/30/2011 gastro intestinal reflexes 32
  33. 33. References• Berne and levy physiology, sixth edition Bruce M.Koeppen, Bruce A. Stanton• Guyton and Hall Textbook of Medical Physiology, 12th Edition.• Human physiology: The Basis of Medicine, 3rd Edition.• Lecture note• Institutional websites10/30/2011 gastro intestinal reflexes 33