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Gulf Medical University

Dr. Sovan Bagchi

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gastrointestinal motility physiology digestive system human anatomy

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This document is a presentation about gastrointestinal motility, including learning objectives, basic structure, and types of motility. It covers the stages of swallowing, and emptying of the stomach.

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Gastrointestinal motility Dr. Sovan Bagchi Professor of Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Learning Objectives Describe the organization of enteric intrinsic nervous system List functions of GI m...

Gastrointestinal motility Dr. Sovan Bagchi Professor of Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Learning Objectives Describe the organization of enteric intrinsic nervous system List functions of GI motility Define peristalsis Describe the mechanism of deglutition Describe the motility of stomach Describe the movements of small intestine and large intestine Explain defecation reflex Basic structure of the alimentary canal Mucosa Epithelium Lamina propria – areolar connective tissue , lymphatic tissue Muscularis mucosae – smooth muscle Submucosa Areolar connective tissue Blood and lymphatic vessels Neurons – submucosal plexus Muscularis Smooth muscle Neurons – myenteric plexus Serosa CT & epithelium Motility in the mouth 1. Mastication (chewing) This process is voluntary taking place in the mouth using teeth, tongue and muscles of mastication. Teeth will cut the food to smaller pieces Mixes food with saliva to soften and lubricate it Saliva contains salivary amylase. 2.Swallowing or Deglutition Swallowing is the movement of food from mouth into the Stomach It is facilitated by secretion of saliva and mucus It involves mouth, pharynx and esophagus It is coordinated by the swallowing center in medulla oblongata and lower pons It involves 3 phases or stages (oral, pharyngeal & esophageal) Phases of Swallowing 1. Oral phase: Voluntary The swallowing starts when the food bolus is forced to the back of the oral cavity and into the pharynx by the movement of the tongue upward and backward against the palate 2. Pharyngeal phase (Involuntary) Tongue sweeps backward bolus into the oro-pharynx Elevation of soft palate and contraction of the upper constrictor muscle of the pharynx to close nasopharynx. Epiglotis and vocal cords shut off the larynx Reflex apnea Relaxation of UES Peristatic contraction begins 3. Esophageal Phase (Involuntary) Begins once the food bolus enters the esophagus Peristalsis pushes the bolus onwards. Peristalsis Wave-like muscular contractions of adjacent segments 1. Circular smooth muscle contract behind, 2. relaxes in front of the bolus, followed by 3. longitudinal contraction (shortening) of smooth muscle. Rate of 2-4 cm/sec. It is taking place through out the GIT is helping in propelling the food Lower Esophageal Sphincter (Cardiac sphincter) At the lower of the oesophagus relaxes to allow the bolus to enter the stomach It is usually closed in between swallowing to prevent gastric reflux Stomach Motility Gastric Filling Gastric Storage Gastric Mixing Gastric Emptying Gastric Filling and storage: The stomach is able to accommodate such a 20 fold change in its volume — During a meal stomach relaxes slightly with each mouthful ➔Receptive relaxation — Receptive relaxation enhances the stomach ability to accommodate with extra volume of food. As the bolus reaches the lower oesophagus: ▪ LES opens ▪ Circular muscle of the proximal 1/3 of the stomach relaxes ▪ This relaxation is vago vagal reflex ▪ Peristalsis then begins in the lower portion of stomach Gastric mixing & emptying The contraction of the gastric pump can be differentiated into three phases: A: phase of propulsion, B: phase of emptying, C: phase of retropulsion and grinding Phase of propulsion Phase of emptying Phase of retropulsion Emptying of liquids with Rapid flow of liquids with Retropulsion of large small particles whereas suspended small particles large particles are retained particles and clearing and delayed flow of large in the buldge of the terminal of the terminal antrum particles towards pylorus antrum 16 Regulation of Gastric emptying Distension of the stomach by the presence of food Secretion of gastrin and increase parasympathetic impulses Stimulate contraction of lower esophageal sphincter, increase motility of the stomach Relax of the pyloric sphincter Gastric emptying Vomiting or emesis The sudden and forceful oral expulsion of the contents of the stomach and sometimes from the intestines It is a basic physiologic protective mechanism, that involves medullary center The vomiting center is activated by; ✓ Distention or irritation in the GIT ✓ Stimuli from various parts of the brain in response to sight, smell or ischemia ✓ Pain or stress ✓ The vestibular apparatus ✓ Increased intracranial pressure 18 Motility of Small intestine Two basic motility patterns exist segmentation and peristalsis. Motility of the small intestine serves 3 functions: 1.Mixing contents with enzymes and other secretions ĺ help digestion 2.Maximizing exposure of the contents to membranes of intestinal cells ĺ help absorption and digestion. 3.Propulsion of contents into the large intestine. The transit time in the Small intestine is 8 – 9 hrs Irritation of small intestine mucosa as in infectious diarrhea causes powerful and rapid peristalsis Small intestine Motility Segmentations Nonadjacent segments of the intestine alternately contract and relax Mix contents with the digestive juices and bring the particles of food into contact with the mucosa for absorption They do not push the intestinal contents along the tract. Migrating motility complexes (MMC) It is type of peristalsis It starts in the lower stomach and pushes chyme forward along the small intestine. Each movement lasts for 10 min. Sweeps the contents towards colon. Motilin hormone and intrinsic plexus are said to be responsible for MMC Motility of Large Intestine Haustration (segmentation in colon) Slow segmenting movements that move the contents of the colon (occur every 30 min) Proximal colon motility is increased by vagus Controlled by the intrinsic plexuses Stimulated by distension Helps in mixing, propulsion and absorption Transit time in colon ranges from 12 – 72 hrs Mass movements (propulsive movements) ĹĹ motility in ascending and transverse colon occurring after a meal Drive the colonic contents to the distal portion of large intestine Occurs 1 – 3 times / day Propels feces towards rectum Occurs during defecation. Triggered by: —Gastrocolic and duodenocolic reflexes —Irritation —Intense parasympathetic stimulation Defecation Reflex Distension of rectum with feces initiates the reflex. Rise in rectal pressure causes desire to defecate Distension stimulate stretch receptors Signals to sacral spinal cord Relaxation of internal anal sphincter through pelvic nerve (parasympthatic), The internal sphincter is a smooth muscle and supplied by pelvic nerve (involuntary) The external anal sphincter is a somatic muscle and innervated by pudendal nerve (voluntary ). During defecation reflex, the external and internal anal sphinctersare relaxed. Learning Resources Text Book: Marieb EN. Human Anatomy and Physiology, 9th Edition, Pearson International Edition; 2014. ISBN-13: 978-1-2920-2649-7. Chapter 23, pp. 863-866. Power-point presentation in the moodle www.gmu.ac.ae COLLEGE OF MEDICINE

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