OS 206: Abdomen and Pelvis: GI Motility PDF
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Uploaded by DazzlingFreedom
University of the Philippines College of Medicine
2024
Carlos R.G. CuaƱo
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Summary
This document, part of the UPCM 2029 curriculum, provides a comprehensive overview of GI Motility, covering functional anatomy, motility patterns, and regulatory mechanisms. Produced by Dr. Carlos R.G. CuaƱo, this guide includes information for the GI system.
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OS 206: ABDOMEN AND PELVIS GI MOTILITY UPCM 2029 | Dr. Carlos R.G. CuaƱo | LU3 A.Y. 2024-2025 ā Exocrine Pancreas OUTLINE...
OS 206: ABDOMEN AND PELVIS GI MOTILITY UPCM 2029 | Dr. Carlos R.G. CuaƱo | LU3 A.Y. 2024-2025 ā Exocrine Pancreas OUTLINE āā Synthesizes digestive enzymes I.ā Introduction C.ā Gastroesophageal āā Also has an endocrine function A.ā Role of Reflux ā Liver Gastrointestinal VIII.ā Gastric Motility āā Produce bile acids to aid in fat digestion System A.ā Functions āā Stores fat B.ā Functional Anatomy B.ā Gastric Emptying āā Detoxification C.ā Feces C.ā Regulation āā Synthesizes serum proteins D.ā General Organization D.ā Retropulsion ā E.g., albumin, globulin, clotting factors E.ā Regulation of GI E.ā Vomiting āā Synthesizes urea from ammonia Activities IX.ā Small Intestine Motility ā Gallbladder II.ā Control of GI Function A.ā Types of Movement āā Stores, concentrates, and releases bile A.ā 6 Basic Processes B.ā Regulation C.ā FECES B.ā GI Motility C.ā Ileocecal Valve C.ā GI Smooth Muscle X.ā Large Intestine Motility III.ā Electrical Activity of GIT A.ā Types of Movement A.ā Pacemaker Cells B.ā Defecation B.ā Smooth Muscles C.ā Rectoanal Inhibitory IV.ā Types of Movement Reflex V.ā Regulation of GI Motility D.ā Clinical Correlation A.ā Specific Motility XI.ā Gallbladder Motility Patterns A.ā Sphincter of Oddi VI.ā Mastication B.ā Clinical Correlation VII.ā Deglutition XII.ā Post Test A.ā Swallowing XIII.ā References B.ā Esophagus LEARNING OBJECTIVES 1.ā Discuss the parts, function, activities and control of the GI system 2.āDiscuss motility and its function 3.āDiscuss the different motility patterns of the Gi organs 4.āDescribe clinical correlations I.ā INTRODUCTION A.ā ROLE OF GASTROINTESTINAL SYSTEM ā Mechanically and chemically break down food into simple components ā Absorption and assimilation ā Supply these nutrients to the body Figure 2. Bristol stool scale ā Store and convert excess nutrients ā Feces contains excretory products āā E.g., glucose gets stored as glycogen and fat āā Heavy metals ā Manufacture materials ā Fe and Cu are major excretions through bile ā Excrete waste products of digestion āā Organic anions and cations ā Facilitate speech ā Drugs excreted in bile ā Stores blood in the liver āā Products poorly or not reabsorbed in intestines ā Regulate blood components ā Cell debris from GI mucosa ā Produce hormones ā Dead white blood cells āā The gastrointestinal tract is also an endocrine organ ā Brown color is due to bacterial action on bilirubin (stercobilin) in the B.ā FUNCTIONAL ANATOMY stool ā Odor āā Due to products of bacterial action like indole, skatole, hydrogen sulfide, mercaptans Fecal Composition ā Water (75%) ā Solid particles (25%) āā Fiber (30%) āā Colonic bacteria (30%) āā Cholesterol and fat (10-20%) āā Inorganic substances (10-20%) ā E.g. Ca2+ and iron phosphate (10-20%) ā Protein (2-3%) D.ā GENERAL ORGANIZATION Figure 1. Overview of parts in the gastrointestinal tract GI TRACT ā Esophagus āā Conduit of chewed food from the mouth to the stomach ā Stomach āā Receives and stores food proximally āā Retains and grinds food distally ā Small intestines āā Continue digestion of chyme āā Absorb nutrients, water, electrolytes, minerals Figure 3. Overview of parts in the gastrointestinal tract ā Colon ā Mucosa āā Store and process fecal matter āā Absorption and secretion āā Absorbs water ā Submucosa ACCESSORY ORGANS āā Supports the mucosa ā Physiologic barriers/partitions āā Blood vessels and lymph vessels āā Upper and lower esophageal sphincter ā Muscularis Externa āā Pyloric sphincter āā Propels food throughout the GI tract āā Composed of an inner circular and outer longitudinal layer Trans 1 TG30: Villanueva, Villanueva, Vitug, Wee, Yadao, Yu, Yu TH: Oribello 1 of 14 ā Serosa kinin (I cells) hydrolyzed endocrine afferent of gastric āā Prevents friction protein terminals, emptying āā Allows movement between the different coils of the GIT pancreatic and H+ acinar cells secretion; Exceptions in the Muscularis Externa stimulation of pancreatic enzyme secretion, gallbladder contraction , inhibition of food intake Secretin Duodenum Protons Paracrine, Vagal Stimulation (S cells) endocrine afferent of terminals, pancreatic pancreatic ductal duct cell secretion (H2O and HCO3-) Gluco-insul Intestine (K Fatty acids, Endocrine Beta cells Stimulation inotropic cells) glucose of the of insulin Figure 4. Histological layers of the stomach and large intestine peptide pancreas secretion (GIP) ā Stomach āā Composed of 3 layers instead of 2 since it is a highly motile Peptide YY Intestine (L Fatty acids, Endocrine, Neurons, Inhibition organ (PYY) cells) glucose, paracrine smooth of gastric ā Outer longitudinal hydrolyzed muscle emptying, protein pancreatic ā Middle circular secretion, ā Inner oblique gastric acid ā Large intestine secretion, āā Composed of two layers but with modifications: intestinal ā Outer longitudinal (Taenia coli) motility, āArranged in three strips over the ascending, transverse, and food intake descending segments of the colon *Table was displayed but not discussed by Dr. CuaƱo āThe three strips fuse at the rectosigmoid area to envelope II.ā CONTROL OF GI FUNCTION the entire surface of the intestines ā Inner circular E.ā REGULATION OF GI ACTIVITIES Figure 6. Control of GI Function (Berne et al., 2018) ā Stimuli: From the GI tract when you have a meal ā Sensors: Activation of both intrinsic and extrinsic sensory afferent pathways āā Brain and Spinal Cord: Emotional states (sight, smell, taste) of food can affect the Enteric Nervous System ā Enteric Nervous System: In turn, both intrinsic and extrinsic neuroreflex pathways will be activated ā Effectors A.ā 6 BASIC PROCESSES ā The digestive system performs six basic processes: ingestion, secretion, motility, digestion, absorption, and defecation. Figure 5. Regulation of GI activities ā Endocrine āā Enteroendocrine cells secrete hormones ā hormones go through Figure 7. Mechanical and Chemical Digestion of Food (Tortora and Derrickson, 2017) the bloodstream ā reaches target cell 1.ā Ingestion - Taking food into mouth ā E.g., Ozempic is a GLP-1 agonist, an enteroendocrine hormone 2.āSecretion - Liberation of water, acids, buffers, and enzymes into Gl āSelectively binds and activates the GLP-1 receptor lumen ā Paracrine 3.āMotility - Mixing & propulsion of food through the GI tract (GIT_ āā Chemical messenger/regulatory peptide ā diffusion into nearby ā Not just the movement of the food, but the MIXING for it to target cell ā ECL ā histamine ā parietal cells interact with the enzymes for adequate digestion ā Autocrine 4.āDigestion - Mechanical and chemical breakdown of food āā Acts on cells of origin 5.āAbsorption - Passage of digested products from GIT into blood or ā Neurocrine lymph āā Neurotransmitters from a nerve terminal ā target cell 6.āDefecation - Elimination of feces from GIT Table 1. Hormonal and Paracrine Mediators in the GI Tract (enlarged in appendix) B.ā GI MOTILITY GI Source Stimulus Pathway Targets Effect ā Mixing and propulsion of food along GIT Hormone for of action release āā Mixing: Distal stomach and intestine; for digestion and absorption Gastrin Gastric Oligopeptid Endocrine ECL cells Stimulation āā Propulsion: Intermittent throughout the alimentary canal antrum (G es and parietal of parietal āā Reservoir: Relaxation and contraction in the stomach and colon cells) cells of the cells to ā Example: Food is stored in the stomach gastric secrete H+ ā Coordinated with secretion and absorption corpus and ECL cells to secrete histamine Cholecysto Duodenum Fatty acids, Paracrine, Vagal Inhibition OS 206 GI Motility 2 of 14 C.ā GI SMOOTH MUSCLE III.ā ELECTRICAL ACTIVITY OF GIT A.ā PACEMAKER CELLS Figure 11. Cells and Electrical Events in the Muscularis ā Like the heart, the GIT has a pacemaker cell called Interstitial Cells of Cajal ā Interstitial Cells of Cajal (ICC) āā Cobbled to the smooth muscles and generate electrical impulses that cause smooth muscles to contract in a coordinated manner āā Located between the circular and longitudinal muscles of the GIT Figure 8. GI Smooth Muscle āā Produces conduction of slow waves which causes depolarization, opening of calcium channels, and produces action ā Spindle shaped potentials ā Autonomic nervous system control ā Involuntary B.ā SMOOTH MUSCLES āā However, the parts of the GIT lined with striated muscle can be ā Dictates the basic movement of the gut contracted voluntarily ā 2 Types: ā Muscular Layer āā Slow wave āā Inner Circular ā Generated by the ICC āā Outer Longitudinal ā Undulating changes in resting membrane potential (N.V. -56 āā Exceptions: mV) ā Esophagus: Upper ā striated, Middle ā striated + smooth, āChanges in activity of Na,K-ATPase pump Lower ā smooth ā Not cause muscle contraction ā External anal sphincter: striated āOnly changes in baseline tone āVoluntary: One can hold in poop/resist the urge to poop ā Depolarization is stimulated by: āStretch āAcetylcholine āParasympathetics ā āā Spike potential ā True action potential (< -40 mV) ā Higher the slow waves = greater spike potentials ā Cause muscle contraction ā Hyperpolarization is stimulated by: āNorepinephrine āSympathetics Figure 9. Circular and Longitudinal Muscles ā When the inner circular muscle contracts, the diameter decreases ā When the outer longitudinal muscle contracts, the length decreases ā The coordinated action of the circular and longitudinal muscles are able to move food throughout the GIT Figure 12.Electrical Activity Of The GI tract. ā Depolarization of slow wave (baseline electrical activity) produced by the Interstitial Cells of Cajal (through calcium influx) and it exceeds the threshold ā Causes the spike potential ā Causes contraction ā The spikes are the true action potentials (higher than slow wave), thus causing muscle contraction EXCITATION-CONTRACTION COUPLING Figure 10. Peristalsis ā Step 1: Contraction of circular muscles behind food mass = Diameter decreases āā Circular muscle is for pushing ā Step 2: Contraction of longitudinal muscle ahead of food mass = Length decreases āā GIT shortens ā Step 3: Contraction of circular muscle layer forces food mass forward ā Depending on where the contraction of the circular and longitudinal muscles happens, it could be simple propulsion or mixing Figure 13. Excitation-contraction coupling in the gut. (Enlarged In Appendix) ā At rest: Upward Movement is due to Ca2+ influx and downward OS 206 GI Motility 3 of 14 movement is due to K+ efflux ā Stimulated: As Spike Potentials Increase, contractions increase ā Inhibited: No Spike Potentials, no contractions but there is muscle tone āā E.g., Fundus of the stomach, sphincters IV.ā TYPES OF MOVEMENT PHASIC ā Short, rhythmic, in bursts āā Mixing and transmit of chyme ā 2 forms āā Peristaltic and segmentation ā Triggered by AP that cause increases cytosolic calcium ā Esophagus, gastric antrum, small intestine Table 2. Summary of muscle contractions [2028 Trans] SEGMENTATION PERISTALSIS Mixing Motility Figure 14. Regulation of GI motility (A) extrinsic (B) intrinsic. ā Local intermittent constrictive ā Brings food further down A.ā SPECIFIC MOTILITY PATTERNS contractions (5-30 secs), then the tract more than Table 3. Transport of food across the GI Tract new contractions occur at segmentation other points in the gut ā Most forward movement Time to Fasting Organ Length (cm) āā Mainly at points between that happens in the traverse Activity the previous contractions intestine Esophagus 30 6-8 sec Quiescent āā Non-orderly āā Contractile ring appears ā Movements push food back around the gut and then Quiescent Stomach 20-30 1-2 hrs and forth moves forward (fundus) ā In small intestine, ā Stimuli for intestinal Small bowel 500 1.5-4 hrs Active segmentation contractions peristalsis: Gut Distension chop chyme 2-3 times per ā Acetylcholine (ACh) Sphincter of 2-4 - Active minute and tachykinins Oddi āā Promoting progressive cause orad contraction Colon 100-150 12-30 hrs Minimally Active mixing of food with ā Vasoactive Intestinal intestinal secretions Polypeptide (VIP) and ā Quiescence: no food āā Exposes food surfaces to Nitric Oxide cause caudad āā UES and LES contracted ā no motility digestive enzymes relaxation ā No obvious contractions in the fundus (only tone is present) *was not discussed by Dr. CuaƱo VI.ā MASTICATION MOUTH TONIC ā Breaks food bolus ā Long, sustained ā Mixes food with salivary secretion āā Limit flow or provide reservoir ā Increase pleasure of eating ā Gallbladder, lower esophageal sphincter, orad stomach, and āā Contact taste receptors ileocecal and internal anal sphincter ā Teeth designed for chewing: āā āOradā = closer to the mouth āā Anterior teeth (incisors) - cutting (55 lbs of force) ā Causes āā Posterior teeth (molars) - chewing (200 lbs of force) āā Repetitive series of spike potentials ā Greater frequency = greater degree of contraction *Obtained from 2028 Trans āā Hormones ā Digestive enzymes act only on surfaces of food particles ā Continuous depolarization of smooth muscle āā Rate of digestion depends on total surface area exposed to āā Continues entry of Ca2+ into cell digestive secretions V.ā REGULATION OF GI MOTILITY ā Grinding the food to fine particulate consistency prevents excoriation of GI tract and increases ease at which food is EXTRINSIC emptied from stomach into succeeding segments ā Involves the autonomic NS ā Increases the rate of digestion since digestive enzymes act only āā Parasympathetic - stimulatory on surfaces of food particles ā Vagus āā Digestion depends on total surface area exposed to the āInnervates digestive secretions āā Esophagus ā Chewing and swallowing are partly voluntary and partly reflex āā Stomach ā Peristalsis pushes food through the esophagus to the stomach āā Pancreas ā LES keeps food from regurgitation to the esophagus āā Small intestine Functions of Saliva and Chewing (2028 Trans) āā Proximal half of Colon ā Pelvic ā Disruption of food to produce smaller particles āInnervates: ā Formation of a bolus for swallowing āā Distal transverse and left side of the colon ā Initiation of starch and lipid digestion āā Sympathetic - inhibitory ā Facilitation of taste ā Thoracolumbar region of the spinal cord ā Production of intraluminal stimuli in the stomach ā Regulation of food intake and ingestive behavior INTRINSIC ā Cleansing of the mouth and selective antibacterial action ā Involves the enteric NS ā Neutralization of refluxed gastric contents āā Myenteric plexus ā Mucosal growth and protection in the rest of the GIT ā Between longitudinal and circular muscle ā Aid in speech ā Motility āā Submucous plexus VII.ā DEGLUTITION ā Local secretion, absorption, contraction A.ā PHASES OF SWALLOWING 1. Oral Phase (0.5 sec) - voluntary āā Bolus between tongue and soft palate āā Soft palate elevates āā Tongue pushes bolus superiorly and posteriorly āā Bolus enters pharynx 2. Pharyngeal Phase (0.5 sec) - respiration interrupted āā Purely reflex āā Avoids distention of abdomen āā Elevation of larynx and closure of glottis āā Pharyngeal constrictors contract āā Bolus into esophagusā 3. Esophageal Phase āā Conduit for solids and liquids from pharynx to stomach B.ā ESOPHAGUS OS 206 GI Motility 4 of 14 ā Reflux occurs during decreased pressure in the LES/Gastroesophageal sphincter ā Causes for gastroesophageal reflux 1.ā Mechanically Incompetent LES a.ā Hypotensive LES (
