Presentation on theme: "Motility function of the gastrointestinal system"— Presentation transcript:
1 Motility function of the gastrointestinal system
2 The 3 major patterns of the digestive tract motility PeristalsisRhythmic segmentationTonic contraction
3 It requires intact enteric nervous system but can Usually the stimulus for peristalsis is distentionIt requires intact enteric nervous system but canbe modulated by the autonomic nervous system
4 Esophageal Function Esophagus is a collapsible muscular tube. It transports food to stomachSecretes mucus with no digestive or absorptive function.Upper oesophagealsphincter (UES)UES closes in between swallowing to:Prevent esophageal contents refluxinto pharynxPrevents air entry into the esophagusDiaphragmLower oesophagealsphincter (LES)LES :Closed in between swallowingPrevents stomach content reflux into esophagus
5 Swallowing or Deglutition Swallowing is the movement of food from mouth into the StomachIt is facilitated by secretion of saliva and mucusIt involves mouth, pharynx and esophagusIt is coordinated by the swallowing center in medulla oblongata and lower ponsIt involves 3 phases or stages (oral, pharyngeal & esophageal)
6 Phases of Swallowing 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
7 Phases of Swallowing 2. Pharyngeal phase (Involuntary) Tongue sweeps backward → bolus into the oro-pharynxElevation of soft palate and contraction of the upper constrictor muscle of the pharynx to close nasopharynx.Epiglotis and vocal cordsshut off the larynxReflex apneaRelaxation of UESPeristatic contraction begins in the upper constrictor muscle → middle & inferior constrictor muscle
8 Phases of Swallowing 3. Esophageal Phase (Involuntary) Begins once the food bolus enters the esophagusPeristalsis pushes the bolus onwards.
9 Esophageal Phase cont… At the lower of the oesophagusLES (Cardiac sphincter) relaxes to allow the bolus to enter the stomachIt is usually closed to prevent gastric reflux
10 Functions of the stomach Storage of ingested food until it is emptied into small intestine.Secretion of HCl and enzymes that begin protein digestion.Stomach mixing movements:Ingested food is pulverized and mixed with gastric secretion ChymeChyme is emptied into the duodenum (gastric emptying)10
11 Four Aspects of Gastric Motility: Stomach Motility FunctionFour Aspects of Gastric Motility:Gastric FillingGastric StorageGastric MixingGastric Emptying11
12 Gastric Filling and storage: The stomach is able to accommodate such a 20-fold change in its volumeQuestion: HOW?Answer: Receptive RelaxationDuring a meal stomach relaxes slightly with each mouthful RECEPTIVE RELAXATIONReceptive relaxation enhances the stomach ability to accommodate with extra volume of food.
13 Gastric emptying & mixing: 11. Peristaltic contraction (PC) originates in the upper fundus → the pyloric sphincter2. The PC becomes more vigorous as it reaches the antrum.3423. The strong PC propels the chyme forward4. A small portion of the chyme is pushed through the “partially” open sphincter into the duodenum55. When PC reaches the pyloric sphincter, the sphincter closes tightly → No further emptying66. The chyme that was not delivered in to the duodenum is forced backward into the stomach for further mixing13
14 Regulation of Gastric emptying Distension of the stomach by the presence of foodSecretion of gastrin and increase parasympathetic impulsesStimulate contraction of lower esophageal sphincter,increase motility of the stomachRelax of the pyloric sphincterGastricemptying
15 Carbohydrates empty > Proteins > fats Distension of the duodenum by chyme, fatty acidsEnterogastric reflexparasympathetic stimulationSympathetic stimulationCCKGastric motilityCarbohydrates empty > Proteins > fatsInhibition of gastricemptying
16 Small Intestine Site of digestion and absorption Divided into 3 regions: duodenum, jejunum, ileumJoins the large intestine at ileocecal sphincterStomach chyme must be transported from duodenum down the full length of the small intestine for digestion and absorption to take place efficiently.Chyme is chopped, churned and mixed with small intestine secretions
17 Small intestine Motility Two types of SI movement1. SegmentationsMix contents with the digestive juices and bring the particles of food into contact with the mucosa for absorptionThey do not push the intestinal contents along the tract.2. Migrating motility complexes (MMC)It is type of peristalsisIt starts in the lower stomach and pushes chyme forward along the small intestine.
18 Ileocecal sphincterIleocecal juncture prevents contamination of the small intestine by large intestine contents.Normally remain partially closed.After a meal gastroileal reflex intensifies ileum peristalsis and forces chyme into caecum.Gastrin cause sphincter relaxation.When caecum distended the contraction of ileocaecal sphincter intensifies
20 Motility of Large Intestine Haustration (segmentation in colon)Slow segmenting movements that move the contents of the colon (occur every 30 min)Controlled by the intrinsic plexusesStimulated by distensionMovement are slow → absorptive and storage functionsMass movements (propulsive movements)↑↑↑ motility in ascending and transverse colon occurring after a mealDrive the colonic contents to the distal portion of large intestineTriggered by:─ Gastrocolic and duodenocolic reflexes─ Irritation─ Intense parasympathetic stimulation20
21 Defecation Reflex Two anal sphincters: Parasympathetic nerveFibers (pelvic nerve)Two anal sphincters:Internal anal sphincter: smooth muscle & NOT under voluntary control.External anal sphincter: striated muscle, under voluntary control & is innervated by the pudendal nerveSkeletal motor nerve (pudendal nerve)
22 Defecation Reflex Mass movement Rectum is distended Activation of stretch receptorsSignals to sacral spinal cordGives desire to defecateThrough pelvic nerve (parasympthatic),relaxation of internal anal sphincterIf the conditions are right:Voluntarily relaxation of external anal sphincter allows defecation.Otherwise, the reflex subsides until the rectum is filled again