General Principles of GI Motility PDF

GIT Block · General Principles of GI Mo4lity Dr. Saif Ahmed MBBS , MD Dr. Sarah Al-Mazidi Assistant Professor Clinical Neurophysiologist Department of PHYSIOLOGY Department of PHYSIOLOGY College of Medicine College of Medicine  1. Describe the...

GIT Block · General Principles of GI Mo4lity Dr. Saif Ahmed MBBS , MD Dr. Sarah Al-Mazidi Assistant Professor Clinical Neurophysiologist Department of PHYSIOLOGY Department of PHYSIOLOGY College of Medicine College of Medicine  1. Describe the major excitatory and inhibitory motor neurotransmi9ers and major diges&ve hormones in the GI tract and how these biomediators a>ect func&on in GI &ssues and cells 2. Describe the neural circuitry driving major GI reBexes and the neural pathways and neurotransmi9ers that accomplish reBex control of GI func&ons 3. Describe the Swallowing ReBex and Esophegeal Gastric Objec&ves Junc&on 4. State the factors inBuencing Gastric Emptying 5. Describe the Mixing and Propulsive movements of the Intes&ne 6. Describe the Defeca&on ReBex.  of/I Structural Organiza4on of GIT GI Layers Intro: sina.io Digestion iii -External Internal ly celluer incase an -gut- mechanical entimes ration - metabolism - - area mastication To asurface parastating - - Submucosal plexus -> Secution Myenteric plexus Motality - -> bet There are 2 layers of plexuses that are connection of nerve fibres : 1) Myenteric plexus (lies between circular and longitudinal muscular layers) 2) Meisner plexus (below submucosa)  FYI * * GI system has its own neurons that governs the secretions and the movement however it is also influenced by external neurons such as the vagus nerve  Control of the diges4ve system Movement of materials along the diges&ve tract is controlled by: – Neural mechanisms mpthatic motality & Sy Intrinsic and Extrinsic myenteric Enteric submucosal - -> Autonomic parasympthatic digestion – Hormonal mechanisms Enhance or inhibit smooth muscle contrac&on – Local mechanisms L Coordinate response to changes in pH or chemical s&muli Intrinsic neural mechanisms refers to the myentric and meisner plexuses Extrinsic neural mechanisms refers to Vagus nerve action and the ANS as a whole  Faster than the hormonal Neural Control of the Fp diges4ve system - motality & Myenteric nerve plexus Also called (Auerbach) ▪ Lies between circular and longitudinal muscularis externa ▪ Controls peristalsis and segmenta&on r Because the muscle layer is always responsible for the movement submucosa -> - Meissner’s nerve plexus ▪ Lies in submucosa ▪ Signals glands secratory However both the plexuses do both jobs of secretion and contraction of muscles But mainly Myenteric controls the contraction and Meissener controls the secretion  Nerve Supply The enteric nervous system is linked to the central nervous system via the autonomic The nerve plexuses in the mucosa, submucosa and muscularis propria are of three types: – cholinergic parasympathe&c (with muscarinic or nico&nic receptors) Stimulation – adrenergic sympathe&c (with both α and β receptors) inhibition So they don’t give ACH nor they will – non-cholinergic non-adrenergic (NANC) give adrenergic response For NANC, the transmi9ers are thought to be either cyclic nucleo&des and ATP or intes&nal hormones (e.g. VIP) or nitric oxide a person given a cholinergicdrug to treathis eye as a sideeffect he will have constipation or Direa Q Neurotranslitter At target organ for NANC what's L erase Constriction and Receptive Operistaltic Push Relaxation Receptpfetiat Prophy [ et para Push GI Above the food is which is constriction by Acetylcholine thehonelo below the food is dilatation Responsiblefor (Relaxation) by VIP and NO regdtit.it c p p This is called receptive relaxation in which the muscles are expecting the food to come so it relaxes and it is carried out by non- cholinergic non-adrenergic  Q1) receptive relaxation is a property of … A- non-cholinergic non-adrenergic (NANC) Q2) which transmitters are responsible for receptive relaxation A- VIP + NO THE PHARYNX AND OESOPHAGUS  Deglu44on Movement of food from the mouth to the stomach is known as Deglu&&on (swallowing) Swallowing is facilitated by salivary and mucuos secre&ons. It occurs in 3 stages... esophages * sphincter Oral Phase is always close to Voluntary prevent the air to come in x Pharyngeal Phase Involuntary Esophageal Phase ·  Nervous control of swallowing E in - It controls the food at all levels but it’s major control is in the involuntary phase in the oesophagus and pharynx. - It moves the food in One Direction only. - if something wrong happens in this centre there will be vomiting  Esophageal Phase Lower Esophageal Sphincter (LES) Anatomically indistinct, it is a Connected to pharynx It is formed by the distal 4 cm of esophageal smooth muscle It normally remains constricted, relaxing only transiently to allow the passage of bolus into the stomach When the pressure of the stomach increases the tightening of the lower oesophageal sphincter will increase this is called anti-reflux Connected to stomach mechanism i.e : if you eat more or drink more the pressure of the stomach will increase so the lower oesophageal sphincter will be closed more strongly  ifGERD Lowes An4-reRux Vomi4ng/Emesis Mechanisms Ant Parskelisis against parstalks LES rapidly regains its normal Forceful expulsion of food from tone (following relaxa&on to stomach allow a bolus to enter the stomach) and thereby Vomi&ng centre is Chemoreceptor prevents reBux. Trigger Zone (CTZ) located in It is capable of increasing “area postrema” in medulla. tone in response to rises in It reverse the action of the swallowing centre intra-abdominal and Smixing f*** A>erent impulses arise by intragastric pressures irrita&on T of GI mucosa, ves&bular and digestion appartus and other organs to s&mulate CTZ. It has no blood brain barrier  GERD- Gastroesophageal ReRux Disease GERD May develop when an&-reBux mechanisms fail. The failure of lower oesophageal sphincter This a condi&on in which the food or ;uid content of the stomach regurgitates into the oesophagus. imp * The regurgitated food or Buid usually contains acid and I pepsin produced by the stomach and can in;ame and damage the lining of the oesophagus leading to heartburn and oesophagi&s and can lead to ulcera&on Q1) which of the following is a pre-cancerous lesion … b then can devolpe A- Pars oesophageal lesion Cancer  Achalasia Cardia- a mo4lity disorder of L Means no movement Oesophagus f Achalasia cardia is a disease characterized by : Momentofoesophagus is zero Nuronal if Messes its internsc Plexuses – aperistalsis in the body of the esophagus – failure of relaxa&on of the lower esophageal sphincter on ini&a&on of swallowing So whatever he eats it will stay in the oesophagus and there will be a big mass above the diaphragm Dysphagia- It means dicculty in swallowing. It may occur due to disorder involving any of the stage of Deglu&na&on The Stomach  PfYI* Structure The stomach is divided into a small area immediately distal to the oesophagus (the cardia) – upper region (the fundus which lies under the led diaphragm) – mid-region or body – the antrum, which extends into the pyloric region Two sphincters: the gastro-oesophageal sphincter and the pyloric sphincter; the la9er is largely made up of a thickening of the circular muscle layer The muscle wall of the stomach has three layers – outer longitudinal – inner circular – innermost oblique layer of smooth muscle  Structure sphincters)  Motor func4ons of Stomach C Storage of food un&l the food can be processed in the stomach, duodenum, and lower intes&nal tract & Mixing of this food with gastric secre&ons un&l it forms a semiBuid mixture called chyme ③ β the futures Slow emptying of the chyme from the stomach into the small intes&ne at a rate suitable for proper diges&on and absorp&on by the small intes&ne  Gastric Mo4lity Mechanical Electrical port part 7 peristal sis - is - Pyloruso. D: Siys FEELS Per ista l si s s Basal Electrical Rhythm J pacemaker BER It consists of cells (cells of cajal) that fires electrical impulses to induce mechanical actions of the whole GI IEiiEi system In case the stomach gets stretched the electricity will build up until it reaches the action potential then it will lead to contraction ERconvertsto peristalsis  Basic Electrical Rhythms [BER] Cyclic Slow waves of depolariza&on in smooth muscle -- cells of Stomach cells of cats β Ini&ated by Pacemaker Cells (outer circular layer of smooth muscle in ‘Body’) BER Itself Rarely Cause Muscle Contrac&on * AS if onlyhappen if u changePA streatch force A threshold APs Paristats Peristalsis of stomach occurs @ 3/min and is coordinated by BER. ·  Stomach Musculature # A ↳ Stomach Musculature Relaxes Before and Ader Food Gets Into it Y Recep&ve Relaxa&on – occurs when food is s&ll In Esophagus (Vagally Mediated and Gastrin-induced) Dr Saif says that we should check whether 2 Adap&ve Relaxa&on – occurs when food is in Stomach it’s true or false if (Local Nerve Plexus) because he’s not 100% sure titre  Gastric Emptying Begins near the middle of the body of the stomach towards pylorus more powerful contrac&ons in pyloric antrum peristalsis near the pylorus – pyloric sphincter closes only small amount of liquid chyme squirts through sphincter chyme bounces back – mixing with gastric contents Peristaltic waves move Peristalsis & mixing most towards pylorus vigorous close to pylorus & The stomach Pylorus pumps small Pylorus forces duodenum act amounts of chyme most of the chyme together as (about 3 ml) into backwards a PUMP duodenum inhibatory - (NO) Rfb aftereating  Gastric emptying S4mulated by The vagus - Gastrin (hormone produced by the stomach) Inhibited by Sympathe&c s&mula&on Hormones SECRETIN, CHOLECYSTOKININ (CCK), GASTRIC - INHIBITORY PEPTIDE (GIP) Fats, acid and hyperosmo&c substances in the duodenum Fear and anxiety  Gastric Emptying Fatty Meal Emptying &me: Fat > protein > carbohydrates THE SMALL INTESTINE - fYI* The most developed structure in small intestine is mucosa because it is associated with absorption and release of enzymes forabsorbtics  Structure The small intes&ne extends from the duodenum to the ileocaecal valve. It is approximately 6 m in length, the upper 40% - the jejunum; the remainder - the ileum. Its surface area is increased by mucosal folds ↑ surface area - absorption It has onger-like projec&ons called villi and the surface area is further increased by microvilli consists of blood vessels, lympha&cs and cells and is covered by epithelial columnar cells that are absorp&ve On its luminal side the epithelial cell has a brush border of microvilli that is covered by the glycocalyx / The crypts of Lieberkühn open into the lumen, between the villi historical feature found in Small intestine ON  Motility of Small Intestine The contractile patterns of the small intestinal muscular layers are primarily determined by integrated neural circuits within the gut wall - the enteric nervous system The CNS and gut hormones also have a modulatory role on motility. The interstitial cells of Cajal lie within the smooth muscle. These mesenchymal cells appear to govern rhythmic contractions Pacemakers found in Judorm During fasting, a distally migrating sequence of motor events termed the migrating motor complexes (MMC) occurs in a cyclical fashion Basic electrical rhythm is electricity released by pacemaker cells This electricity causes basic amount of contraction This basic amount of contraction is called migrating motor complexes (MMC) during fasting contractions gets stronger  Migra4ng Motor Complexes (MMC) is Mechanical weak house cleaning MMC is motor ac&vity in smooth muscle of GIT, migra&ng to distal ileum and increases during fas4ng fasting: inthe - Stomach -> X contraction Small intestine to contraction (random movement ( Due to the MMC Each MMC cycle consists of 3 phases: – period of motor quiescence (phase I) – period of irregular contrac&le ac&vity (phase II) – a short (5-10 min) burst of regular phasic contrac&ons (phase III) Each MMC cycle lasts for approximately 90 -120 minutes and is completely inhibited by meals. - - Func4on: propel secre&ons and residual food towards the colon  Mo4lity of Small Intes4ne Ader a meal, the MMC pa9ern is replaced by irregular contrac&ons lasts typically for 2-5 hours, depending on the size and nutrient content of the meal The irregular contrac4ons of the fed pa9ern have a mixing func&on, moving intraluminal contents The difference between peristalsis and migrating motor complex (MMC) is that peristalsis are set of strong movements that are unidirectional and help push the food whereas the migrating motor complex are slow waves that has a cleaning function and can’t push the food Segmenta4on and Peristal4c Movements Both Mixing  is a 8 al but peristatic also Pushing Segmenta4on Mixing movements Ring-like contrac&ons at regular intervals (Contrac&on of circular muscles) Moves the chyme increasing its exposure to mucosal surface for absorp&on The difference between peristalsis and segmentation is that peristalsis contracts in a way that pushes the food where is constricts before the food relaxes after the food whereas segmentation contracts in a way that mixes the food and do not push it ⑨ No propulsion No direction opposite to peristalsis  Peristalsis Propulsive movements that propels the intes&nal contents (chyme) toward the large intes&ne. Occurs at any part of small intes&ne, most frequent in duodenum then slows down in jejunum & ileum -> Ss Stomach Peristalsis at Proximal intes4ne >>> faster than terminal intes4ne not week Peristal&c movements are weak, and con&nues unidirec&onally towards the anus. This is called Law of Gut. Net movement of chyme ~ 1 cm/min 3-5 hours journey from pylorus to ileocecal valve intesti food diffuse  L 0 fat The circular muscle contraction inhibits the food from going back  Gastroileal reRex Gastroileal reRex ▪ When the food leaves the stomach , it triggers relaxa&on of ileocecal valve. Stomach stretches >> Vagus is stimulated >> ileocecal valve opened o This is vagally mediated reBex. ▪ This allows chyme to pass from small intes&ne into large intes&ne The Large Intestine  Movements of the Colon The proximal half of the colon is concerned principally with absorp&on, and the distal half with storage. b Mainly absorption of water and some ions The movements of the colon are normally slow The movements are similar to those of the small intes&ne and can be divided once again into * – mixing movements- segmenta&on [ – propulsive movements-peristalsis.  Defeca4on ReRex Presence of Faeces in RECTUM · Stretch Receptors in the wall gets stimulated (Afferent fibres of Pelvic Contraction of Ant Abdominal muscles nerve) Tonic relaxation of Internal Anal sphincters But External Anal sphincter remains closed Series of peristaltic contractions of rectum moving towards anus (SHORT Relaxation of Puborectal sling REFLEX LOOP) Desire to DEFAECATE, a coordinated Actual release of Ifaeces requires a reflex (S2, S3, S4) empties conscious effort to relax EXTERNAL Descending colon, Sigmoid colon into SPHINCTER by Pudendal nerve Rectum (LONG REFLEX LOOP)  Defeca4on ReRex seas a streatch is in our control Fecal incontence wit happen due to external spherder fail causes I Gastrocolic ReRex To explain the defecation reflex - Once there is digested food in the rectum the walls of rectum gets stretched so the sensory fibres will send signals to The spinal cord Both segmenta&on and peristal&c movements which will cause some reflexes that contracts the walls of rectum and relaxes the internal Anal sphincter. occur frequently following meals. - However The external Anal sphincter overrides the internal anal sphincter so defecation does not occur until the external Anal sphincter relaxes which is voluntary controlled The disten&on of stomach by food ini&ates contrac&on in rectum and desire to defecate, called as Gastrocolic ReBex.  Gastrocolic Reflex Both segmentation and peristaltic movements occur frequently following meals. The distention of stomach by food initiates contraction in rectum and desire to defecate, called as Gastrocolic Reflex. This is comman in children and may be due to action of gastrin on the colon. whenever she feed her child that's Mother Complains the time he poops gastrocolic Reflex Normal Igg Queries invited: [email protected] [email protected]