Neural Regulation of GIT PDF

neural regulation of GIT BY DR. Ali mohmed  INNERVATION OF GIT A.Intrinsic innervation local 1.Myenteric/Auerbach plexus 2.Submucosal/Meissners plexus. B.Extrinsic innervation- Higher centre 1.Parasympathetic -2.Sympathetic  Lies in the wall of the gut, beginning in the es...

neural regulation of GIT BY DR. Ali mohmed  INNERVATION OF GIT A.Intrinsic innervation local 1.Myenteric/Auerbach plexus 2.Submucosal/Meissners plexus. B.Extrinsic innervation- Higher centre 1.Parasympathetic -2.Sympathetic  Lies in the wall of the gut, beginning in the esophagus and - extending all the way to the anus controlling gastrointestinal movements and secretion. (1) an outer plexus lying between the longitudinal and circular muscle layers, called the myenteric plexus or Auerbach’s plexus, - controls mainly the gastrointestinal  2) an inner plexus, called the submucosal plexus or Meissner’s plexus, that lies in the submucosa. - controls mainly gastrointestinal secretion and local blood flow  myenteric plexus The myenteric plexus consists mostly of a linear chain of many interconnecting neurons that extends the entire length of the GIT When this plexus is stimulated, its principal effects are (1) increased tonic contraction, or “tone,” of the gut wall, - (2) increased intensity of the rhythmical contractions, - (3) slightly increased rate of the rhythmical contraction, - (4) increased velocity of conduction of excitatory waves along the gut wall, causing more rapid movement of the gut peristaltic waves  submucosal plexus - The submucosal plexus is mainly concerned with controlling function within the inner wall - local intestinal secretion, local absorption, and local contraction of the submucosal muscle Neurotransmitters: - (1) Ach (7) substance P - (2) NE. (8) VIP - (3)ATP (9) somatostatin - (4) 5– HT (10) bombesin - (5) dopamine (11) metenkephalin - (6) cholecystokinin (12) leuenkephali  Higher centre innervation the extrinsic sympathetic and parasympathetic fibers that connect to both the myenteric and submucosal plexuses. - the enteric nervous system can function on its own, independently of these extrinsic nerves, - stimulation by the parasympathetic and sympathetic systems can greatly enhance or inhibit gastrointestinal functions. - sensory nerve endings that originate in the gastrointestinal epithelium or gut wall and send afferent fibers to both plexuses of the enteric system, - as well as (1) to the prevertebral ganglia of the sympathetic nervous system, (2) to the spinal cord, and (3) in the vagus nerves all the way to the brain stem. These sensory nerves can elicit local reflexes within the gut wall  Autonomic Control Parasympathetic the cranial parasympathetic nerve fibers - mouth and pharyngeal regions of the alimentary tract, esophagus, stomach, and pancreas and somewhat less to the intestines down through the first half of the large intestine. - The sacral parasympathetics originate in the 2nd, 3rd & 4th sacral segments of the spinal cord and pass through the pelvic nerves to the distal half of the large intestine and all the way to the anus. - The sigmoidal, rectal, and anal regions are considerably better supplied with parasympathetic fibers than are the other intestinal areas - defecation reflexes.  Sympathetic Innervation spinal cord between segments T-5 and L-2. - Pre ganglionic - sympathetic chains- celiac ganglion and various mesenteric ganglia– post ganglionic - innervate essentially all of the gastrointestinal tract–inhibitory - (1) to a slight extent by direct effect of secreted NE to inhibit intestinal tract smooth muscle - (2) to a major extent by an inhibitory effect of NE on the neurons of the entire enteric nervous system  Afferent Sensory Nerve Fibers sensory nerves can be stimulated by (1) irritation of the gut mucosa, (2) excessive distention of the gut, (3) presence of specific chemical substances in the gut  Gastrointestinal Reflexes 1. Reflexes that are integrated entirely within the gut wall enteric nervous system– secretion, peristalsis, mixing contractions, local inhibitory effects 2. Reflexes from the gut to the prevertebral sympathetic ganglia and then back to the GIT - signals from the stomach to cause evacuation of the colon (the gastrocolic reflex), - signals from the colon and small intestine to inhibit stomach motility and stomach secretion (the enterogastric reflexes), - reflexes from the colon to inhibit emptying of ileal contents into the colon (the colonoileal reflex)  3. Reflexes from the gut to the spinal cord or brain stem and then back to the GIT. - (1) 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 secretory activity; - (2) pain reflexes that cause general inhibition of the entire GIT; - (3) defecation 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  MIGRATING MOTOR COMPLEX Electrical and motor activity in gut smooth muscles during interdigestive stage Duration : 90-100 min in each cycle Rate of movement is 5cm/min from oral to aboral site Phase 1-Quescent period with no activity Phase 2-Period of irregular activity Phase 3-Period of regular activity Initiated by motilin Gastic secretion,bile flow,pancreatic secretion increases MMC Food abolish MMC by inhibiting motilin  thanks