Transcript 幻灯片 1
IV MOTILITY OF THE SMALL INTESTINE 1 Function of Intestinal Motility (1)To mix chyme with digestive secretion (2)To bring fresh chyme into contact with the absorptive surface of the microvili (3)To propel chyme toward the colon 2 Types of small intestinal movement 1. Tonic contraction: the base of the other contractions 2. Segmentation contractions (1) def. When a portion of the small intestine becomes distended with chyme, the stretch of the intestinal wall elicits a rhythmical contraction and relaxation of localized circular muscles spaced at intervals along the intestine, (2) function: mix the chyme with the digestive juice increase its exposure to the mucosal surface 3 Types of small intestinal movement 3. Peristalsis: propels the small intestinal contents towards the large intestines peristaltic rush：initiated by the harmful stimulation 4. MMC: Occurs during fasting state moves any undigested material still remaining in the small intestine into the large intestine prevents bacteria from remaining in the small intestine long enough to grow and multiply excessively 4 Segmentation: mix contents to promote digestion & absorption 5 Peristalsis • Distinctive pattern of smooth muscle contractions that propels foodstuffs distally through the esophagus and intestines • Mediated by…. • Local, intrinsic nervous system • Ex: peristalsis is not affect to any significant degree by vagotomy or sympathectomy 6 Small Intestinal Motility Peristalsis: movement along the tract 7 Peristalsis 8 Figure 24.4 peristalsis 9 Peristalsis of the small intestine 10 http://medweb.bham.ac.uk/research/toescu/Teaching/OverviewGITY2.html Peristalsis – law of intestine 11 Berne et al., 2004 Peristalsis – law of intestine 12 Berne et al., 2004 Peristalsis – law of intestine 13 Berne et al., 2004 Peristalsis – law of intestine 14 Berne et al., 2004 Peristalsis – law of intestine 15 Berne et al., 2004 Peristalsis – law of intestine • Bolus of food →Mechanical distension and mucosal irritation → stimulates afferent enteric neurons → 2 effects 1. Excitatory motor neurons above the bolus activated → contraction of smooth muscle above the bolus • Via Ach, substance P 2. Inhibitory motor neurons → stimulate relaxation of smooth muscle below the bolus • Via nitric oxide, vasoactive intestinal peptide and ATP 16 Control of Intestinal Motility – Neuronal Mixing – segmentation Frequency set by slow waves (12/minute duodunum) additional control: myenteric plexus Propulsion – peristalsis Local reflex – stretch causes relaxation distal and contraction proximal (Bayliss – Starling law of the intestines) Moves bolus through intestines Intestino-intestinal reflex – extrinsic nerves Local stretch in one area inhibits contraction in rest of 17 bowel Movement in Small Intestine Peristalsis (ou propulsivos) e Segmentation (mixing) 18 http://medweb.bham.ac.uk/research/toescu/Teaching/OverviewGITY2.html Central and peripheral control of contractile patterns Vagal centre Intestinal wall Vago-vagal reflexes Interneurons Integrating circuits Sensory neurons Motorneurons Program circuits Contractile patterns Enteric nervous system Intestinal lumenl Peptide (CCK) Receptors Glucose - Osmolality Long chain fatty acids Amino acids Luminal stimuli elicit vago-vagal reflexes which activate integrating and program circuits of the enteric nervous system. These activate specific motorneurones responsible for specific contractile 19 patterns. Control of Intestinal Motility – Hormonal Gastrin CCK Secretin + motility -- Glucagon 5-HT VIP Motilin GIP 20 Ileocecal Valve • What it is • Opening to large intestines • Function: (1) prevent the repulsion (2) control the emptying • normally closed. Short-range peristalsis in terminal ileum and distension relaxes IC sphincter --> small amount of chyme is squirted into the cecum. • Distension of cecum contracts IC sphincter. • Gastro-ileal reflex: enhances ileal emptying after eating. 21 • The hormone gastrin relaxes ileocecal sphincter. V. GASTROINTESTINAL MOTILITY DURING FASTING STATE 22 Gastric motility on fasting “Migrating Motor Complex, MMC” Occurs during fasting To clear undigested food particles Peristaltic contractions sweep down stomach and duodenum – pylorus relaxes Pattern of contraction approx every 90 min Slow peristaltic waves sweeping whole of GI tract 23 Thought to be controlled by motilin (胃动素） 24 MMC(migrating motor complex) • PhaseⅠ: Almost have no contractions 40-60 min • PhaseⅡ: have contractions, only have few 30-45 min • PhaseⅢ: have continuous contractions 5-10 min 25 The interdigestive motility consists of three phases III Interdigestive Cycles Phases II I Phase III Stomach Phase III Pylorus Duodenum Accumulation of residues of chyme Jejunum Phase I Contraction of reservoir Forceful peristaltic waves Motor quiescence of stomach and duodenum III Phase II Sporadic peristaltic waves Segmenting contractions and single peristaltic waves Phase II Motor quiescence Ileum Phase I Phase III The phase III of the migrating motor complex (of dog) Originates simultaneously at the stomach and duodenum 26 Migrates within 90 to 120 minutes along the small intestine Importance of MMC 1.Sweep the contents of the small intestine towards the colon Housekeeper of the small intestine 2.Inhibit the migration of colonic bacteria into the terminal ileum 27 VI MOTILITY OF THE COLON 28 Large intestine • Functions • Absorption of water and electrolytes • Storage of feces • In non-ruminant herbivores, fermentative digestion and absorption of nutrients • Motility patterns • mixing (form haustrations) • propulsive (mass movements) 29 Segmentation in large intestine • Haustration: （结肠袋） modified form of segmentation in which intense, local contraction of circular muscle causes large intestine to appear to bulge into sacs 30 Mass movement • Occurs in colon; also known to occur in equine cecum • Period of intense propulsive activity that moves entire contents of colon distally toward rectum • Contractions progress for long distance such that long length of colon contracts as a unit • Entry of fecal matter into recturn triggers defecation reflex 31 Mass Movement 32 Defecation Defecation Reflex initiated when rectal walls stretch parasympathetic reflex walls of the sigmoid colon and the rectum to contract & relaxation of the anal sphincter External sphincter control is voluntary control If defecation is delayed: the reflex stops until the next mass movement 33