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 (, haustrations, mass movements) ______

➢ LO4 - Define how we remove indigestible matter (anatomy of the ano-rectum, defecation and external anal sphincter control) ______

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Slide 3 LO2 ______Swallowing (deglutition)

Phase I - ORAL Phase II - PHARYNGEAL Phase III - OESOPHAGEAL VOLUNTARY INVOLUNTARY INVOLUNTARY ______

______

______• Food bolus formed by • rises • UOS contracts mastication • closes • Bolus moved by peristalsis • moves up and • contracts • LOS relaxes backwards • UOS relaxes Pharynx ______UOS Pharynx

Oesophageal ______body Tactile/distension STEM Striated muscle receptors LOS ______Smooth muscle UOS relaxes

Slide 4 ______Entry of food into the ______

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 pressure Vagal efferent ______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 & ______

29% duodenum III – , 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 ______

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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

______Spinal cord Spinal Distention + ______Food + in rectum Ach duodenum Food in Colon stomach ______VIP + FAECES ATP Mass IAS - ______+ movements - EAS ______Pudendal anus Faeces nerve ______Defaecation reflex