Slide 1 Year 1 MBChB – ___________________________________ Gastrointestinal system ___________________________________ I’ve got that gut feeling - motility in the GI tract ___________________________________ Prof. Barry Campbell ___________________________________ Infection Biology & Microbiomes, IVES ___________________________________ [email protected] http://pcwww.liv.ac.uk/~bjcampbl/gimotility.htm ___________________________________ ___________________________________ School of Medicine @UoLmedicine Slide 2 ___________________________________ Learning Outcomes: ___________________________________ ➢ LO1 - Explain the integration and control mechanisms of swallowing (oral, pharyngeal and oesophageal phases) and control ___________________________________ of lower oesophageal sphincter function. ➢ LO2 - Define the motility patterns in fasted and fed states of the intestinal tract ___________________________________ ➢ LO3 - Define motility in the small and large intestine (peristalsis, haustrations, mass movements) ___________________________________ ➢ LO4 - Define how we remove indigestible matter (anatomy of the ano-rectum, defecation and external anal sphincter control) ___________________________________ ___________________________________ Slide 3 LO2 ___________________________________ Swallowing (deglutition) Phase I - ORAL Phase II - PHARYNGEAL Phase III - OESOPHAGEAL VOLUNTARY INVOLUNTARY INVOLUNTARY ___________________________________ ___________________________________ ___________________________________ • Food bolus formed by • Soft palate rises • UOS contracts mastication • Epiglottis closes • Bolus moved by peristalsis • Tongue moves up and • Pharynx contracts • LOS relaxes backwards • UOS relaxes Pharynx ___________________________________ UOS Pharynx Oesophageal ___________________________________ body BRAIN Tactile/distension STEM Striated muscle receptors LOS ___________________________________ Smooth muscle UOS relaxes Slide 4 ___________________________________ Entry of food into the stomach ___________________________________ LOS = lower oesophageal sphincter BRAIN ___________________________________ Ach = acetylcholine STEM VIP = vasoactive intestinal polypeptide Vagal NO = nitric oxide afferent fibre ___________________________________ Crural ___________________________________ diaphragm Ach Phrenic nerve LOS VIF (VIP/NO) ___________________________________ VEF (Ach) LOS Vagal efferent pressure ___________________________________ fibres Slide 5 LO2 ___________________________________ Gastric motility ___________________________________ lower oesophageal sphincter Pyloric Fundus ___________________________________ sphincter “Pacemaker Duodenum zone” - peristaltic ___________________________________ contractions Corpus “acid-secreting” ___________________________________ Antrum “muscular pump” ___________________________________ ___________________________________ = retropulsion Slide 6 LO2 ___________________________________ Control of smooth muscle contraction – Interstitial cells of Cajal are pacemakers of the gut ___________________________________ ICC cell network Slow wave conducted to smooth muscle Slow wave mechanism ___________________________________ L type Ca2+ current & action potential mechanism Action potentials ___________________________________ 25 mV BER ___________________________________ 1.5g ___________________________________ Mechanical recording Basal electrical rhythm (BER) originates in ICC, but itself does not cause contraction; when spike potentials occur at maximum depolarisation of BER due to ___________________________________ Ca2+entry, the result is contraction Slide 7 LO2 ___________________________________ Motility in the interdigestive period - The Migrating Myoelectric Complex (MMC) ___________________________________ 71% antrum III – motilin, ghrelin & vagus nerve ___________________________________ 29% duodenum III – somatostatin, Serotonin (5-HT) and xenin ___________________________________ Phases of MMC Distal small intestine ___________________________________ III ~130 min Feeding II disrupts the I IV Colon cycle ___________________________________ I - quiescence; II - random contractions; III - burst of contractions (max. ___________________________________ amplitude & duration); IV - rapid decrease of contractions. Slide 8 LO2 ___________________________________ LO3 Intestinal movement - segmentation Alternate contraction and relaxation of adjacent ___________________________________ segments causes thorough mixing of food contents ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 9 LO2 ___________________________________ LO3 Intestinal movement - peristaltic reflex Animation at www.westga.edu/~lkral/peristalsis/ Ach = acetylcholine NO = nitric oxide ___________________________________ interneurons interneurons > TK = tachykinin VIP = vasoactive intestinal > > > TK/ACh ACh ACh polypeptide Intrinsic 5-HT = 5-hydroxytryptamine ___________________________________ primary (serotonin) afferent Excitatory Inhibitory neurons motor motor ___________________________________ (IPAN) neurons neurons > > ACh/TK Distension VIP/NO ___________________________________ (5-HT) Circular smooth muscle Orad Caudad ___________________________________ ___________________________________ Ascending contraction Descending relaxation Slide LO2 ___________________________________ LO3 Removing indigestible material – 10 reflexes in the colon and rectum ___________________________________ Spinalcord Distention + ___________________________________ Food + in rectum Ach duodenum Food in Colon stomach ___________________________________ VIP + FAECES ATP Mass IAS - ___________________________________ + movements - EAS ___________________________________ Pudendal anus Faeces nerve ___________________________________ Defaecation reflex .