Slide 1Slide 2Slide 3Interstitial Cells of CajalContraction will occur when threshold is reachedSlide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20GI Motility• Movement of food from the mouth to the anus•Mechanically mixing food to break it into smaller particles and to mix with digestive juicesServes two important functionsMuscle types involved in GI motility•Muscles of mouth, pharynx ,upper esophagus, and external anal sphincter are striated and innervated by somatic motor neurons. •Muscles of the rest of GI tract are smooth and innervated by autonomic neurons.GI Motility includes the following processes:•Ingestion: Taking food into the mouth.•Mastication: Chewing the food and mixing it with saliva.•Deglutition: Swallowing the food.•Peristalsis and Segmentation: Rhythmic, wavelike contractions (peristalsis), and mixing contractions in different segments (segmentation) move food through the GI tract.•Defecation: Elimination of solid, semisolid, and/or liquid waste from the GI tract via the anus.GI Motility part 2•Smooth muscle is an involuntary non-striated muscle.•GI smooth muscle contracts spontaneously, driven by pacemakers•Cells are electrically connected by gap junctions•Different regions exhibit different types of contractions•Tonic contractions•Phasic contractions•Slow wave potentials•3-20 per min (depends on segment of GI tract)•Not all result in contractionGI Motility part 3General Characteristics of GI smooth muscle:Interstitial Cells of Cajal•Pacemaker cells•Basic electrical rhythm•Slow waves•3-5 per min stomach•12-20 per min small intestine•6-8 per min colon•Gap junctions•Amplitude & frequency modulated by extrinsic & intrinsic nerves and hormones •Excite: acetlycholine, substance P•Inhibit: VIP, NO•Slow waves that are not accompanied by an action potential elicit little or no contraction of smooth muscle•Strength of contraction dependent upon number of action potentials.Contraction will occur when threshold is reachedContraction of GI smooth muscle•Calcium•CaM: calmodulin•MLCK: myosin light-chain kinase•ATP•Phosphorylation•Actin•MyosinMotor Patterns of the Small Intestine1.Peristalsis2.Segmentation3.Migrating motor complex (MMC)Figure 21-4 - OverviewPeristalsis and SegmentationMigrating Motor ComplexChewing and Swallowing•Chewing•Serves to:•Mixing food with saliva to lubricate and facilitate swallowing•Reduces size of food particles to facilitate swallowing•Mixes ingested carbohydrate's with salivary amylase to begin carbohydrate digestion.•Both voluntary and involuntary (e.g., evoked reflexes initiated by food in the mouth).•Mechanoreceptors•Relayed information to Brain stem•Results in the orchestration of reflex oscillatory pattern of muscles involved in chewing•Swallowing•Both voluntary and involuntary (i.e., reflex)•Reflex portion controlled by the swallowing center in the medulla evoked by the presence of food in the mouth.•Vagus and glossopharyngeal nerves provide both afferent and efferent pathways between sensory neurons, swallowing center, and the striated muscle of the pharynx and upper esophagus. •Three phases•Oral phase•Pharyngeal phase•Esophageal phaseOropharyngeal stage of swallowing Oral Phase1. Muscles of mouth and tongue mix food with saliva and create bolus of food to be swallowed.2. Skeletal muscle pushes food to back of oral cavityPharyngeal Phase3. Complex reflex involving nerve coordination of skeletal muscle4. closes the epiglottis5. opens the upper esophageal sphincter6. propels food into the esophagusThe oropharyngeal stage is the last voluntary act in processing food until the anal end of the GI tract.Structures of the upper gastrointestinal tract1. Upper esophageal sphincter(UES) opens, bolus of food enters the esophagus, then the UES closes.2. Primary peristaltic contraction forces the bolus of food down the esophagus.3. Lower esophageal sphincter (LES) opened by peptidergic fibers in the vagus nerve that release vasoactive intestinal peptide (VIP) as their neurotransmitter.4. Orad region of the stomach (upper portion) relaxes by a phenomenon of “receptive relaxation”.The function of motility in the esophagus is to propel the food bolus from the pharynx to the stomachGastric emptying and mixing as a result of peristaltic contractions50% of stomach contents emptied2.5 to 3 hoursTotal emptying of the stomach 4 to 5 hours50% emptying of the small intestine2.5 to 3 hoursTransit through the colon 30 to 40 hoursGI Transit TimeHow is motility regulated?•GI hormones•Neural activity•Cholecystokinin (CCK)•Secreted by endocrine I-cells of duodenum.•Receptors found on smooth muscle cells through out entire gut (esophagus, stomach, small intestine, colon). •Inhibits gastric emptying•Stimulates intestinal and colonic motility•Motilin•Secreted by endocrine M-cells found in the crypts of the small intestine.•High levels secreted between meals•Increases the “migrating myoelectric complex”•“housekeeper of the gut”GI Hormones that Influence GI Motility•Neural activity •Myenteric plexus•Excitatory: Acetylcholine, Substance P•Inhibitory: Vasoactive Intestinal Peptide (VIP), nitric oxide•Extrinsic nerves•Parasympathetic•SympatheticHow is motility regulated? Part 2The various segments of the GI tract are separated by six sphincters that control the flow of material along its axis.1. Upper esophageal sphincter2. Lower esophageal sphincter3. Pyloric sphincter4. Ileocecal sphincter5. Internal anal sphincter6. External anal sphincterA SEVENTH sphincter, The Sphincter of Oddi, controls the flow of the secretory products of both the pancreas and liver into the duodenum.Only the UES and the external anal sphincter consist of striated muscle. The rest are made up of smooth muscle.Important Points to Consider1. How is the term “motility” used in reference to GI physiology?2. What are types of muscle are found in the GI tract?3. Voluntary vs Involuntary actions? What is a reflex?4. What is the difference between and functions of peristalsis and segmentation?5. Describe the electrical activity of smooth muscle?6. What is a migrating electrical complex? What is its function?7. How is smooth muscle contraction