Motility of GIT, 2024 Dr. Aliya PDF

‫بسم هللا الرحمن الرحيم‬ ‫‪20.11.2024‬‬ Motility Of The Gastrointestinal Tract (GIT) Dr. :Aliya Elamin B.1.2 Ref. Guyton 14th edition, Unit X11, Chap: 63, PP: (787-794) & Chap: 64, PP: (797-805) ...

‫بسم هللا الرحمن الرحيم‬ ‫‪20.11.2024‬‬ Motility Of The Gastrointestinal Tract (GIT) Dr. :Aliya Elamin B.1.2 Ref. Guyton 14th edition, Unit X11, Chap: 63, PP: (787-794) & Chap: 64, PP: (797-805)  Learning Objectives At the end of the lecture students should be able to describe: 48. What does the central nervous system consist of? What is the relation between the CNS, ANS and ENS? ( PP: 789- 791) 49.What is the difference between phasic & tonic contractions in the gastrointestinal tract? where do these types of contraction occur? (P.789) 50.Describe the voluntary Stage of Swallowing (P. 797) 51.Describe the mechanics of the pharyngeal stage of swallowing (P. 798 -799 ) 52.What is the difference between primary & secondary peristalsis (P. 799) 53.What are the functions of the stomach? (P.799) 54.What causes retropulsion? what is its significance? How are peristaltic contractions (slow waves) generated in the stomach? (P. 800) 55.What are the main consequences of a pyloric spasm? (slides 28,29) (P. 801) 56.What causes the motility of the small intestine? What are the functions of this motility? (PP.802-804) 57.What is the function of the interstitial cells of Cajal? (P. 788) 58.Describe the postprandial & interdigestive motility patterns in the stomach & small intestine ( PP. 792-793) 59.What are the main functions of the large intestine? (P. 804) 60.What are mass movements? what is their relationship with the hustra? ( PP. 804-805) 11/19/2024 3  Neural Control of GIT Functions A. Intrinsic component B. Extrinsic component Enteric Nervous System [ENS] Autonomic Nervous System [ANS] ≡ Symp.& Parasymp. NS 2 Plexuses Sympathetic nervous system: Symp. NS, Parasympathetic nervous system: Parasymp.NS ENTERIC NS = ENS 1. An outer plexus, (myenteric plexus) or Auerbach's plexus: Between longitudinal & circular muscle layers → Controls GIT movements ENS Can direct all functions of the 2. An inner plexus, (Meissner’s plexus) GIT, even in the or submucosal plexus: In submucosa absence of extrinsic → Controls GIT secretions & local BF innervation  Stimulation↑ activity Extrinsic component of the entire ENS 1. Parasymp. NS ↑Activity of most Postganglionic neurons GIT functions located in Myenteric & submucosal plexuses - ↑ Peristalsis & - Relaxing sphincters Rapid propulsion of contents Enteric nervous system: ENS - ↑ Secretion Extrinsic component 2. Symp. NS 2. (NE) inhibit (ENS) neurons Inhibits activity of GIT by: 1. Direct effect of secreted (NE) → inhibit GIT Strong stimulation smooth muscle - Inhibits peristalsis & (Except mucosal muscle) -↑Tone of sphincters Slowed propulsion of food -↓Secretion Constipation Enteric nervous system: ENS, Norepinephrine: NE Sensory nerve endings Many afferent sensory nerve fibers innervate the gut Stimulation: Irritation, distention, chemical Cause excitation or, inhibition of intestinal movements or secretions Intrinsic component Extrinsic component Autonomic NS Enteric NS ↑ motility & Outer plexus (myenteric Parasymp. secretions NS plexus) or Auerbach's plexus ↓motility & Controls GIT movements Symp. NS secretions An inner plexus, (Meissner's plexus) or submucosal plexus Controls GIT secretions & local BF Afferent sensory nerve fibers er  Relationship between CNS - ANS - ENS Autonomic NS is the part of the peripheral NS ≡ »» involuntary control & regulates basic visceral functions through the ENS 11/19/2024 10  Membrane Potentials In Intestinal Smooth Muscle Resting membrane potential (RMP) = Between −50 & −60 mv  Averages : − 56 mv When the peaks of the slow waves → more +ve than −40 mv, spike potentials appear on these peaks Slow waves: Basic electrical rhythm (BER) 11/19/2024 11 Interstitial Cells of Cajal, Act as electrical pacemakers Form a network with each other Between the smooth muscle layers With synaptic-like contacts to smooth muscle cells Possess Cyclic changes in membrane potential? Due to special ion channels: That periodically open & produce inward (pacemaker) currents → Generate slow wave activity: slow, undulating changes in RMP =BER Slow waves: Entry of Na+ not Ca++ [no contraction]  Phasic & Tonic Contractions Phasic contractions: Tonic contractions: - Occur rhythmically - Maintained contraction without - Determined by the relaxation (mins-hrs) frequency of the - Not associated with slow waves “slow waves” - ↑ or ↓ in intensity but continues - Periodic contractions Causes: followed by relaxation - Continuous repetitive spike potentials - Hormones - Continuous entry of Ca++ → interior of the  Esophagus & cell small intestine  Sphincters Functional Types of Movements in GIT 1. Propulsive Movements - Peristalsis A contractile ring appears around the gut & then moves forward Any material in front of the contractile ring is moved forward 2. Mixing Movements: Differ in different parts of the GIT e.g. - Peristaltic contractions at sphincters - Local intermittent constrictive contractions  Swallowing (deglutition) 2 3 1 Pharyngeal Voluntary Stage Esophageal Stage (Mouth) Stage  1.Voluntary Stage of Swallowing - Mouth When food is ready for swallowing → "voluntarily" squeezed posteriorly → pharynx By pressure of the tongue upward & backward against the palate From here on, swallowing becomes entirely- automatic cannot be stopped 11/19/2024 16 2. Pharyngeal Stage As food enters posterior mouth & pharynx → Stimulates epithelial swallowing receptor areas, around opening of the pharynx - (Tonsillar Pillars) Impulses → brain stem → (deglutition - swallowing center) → »»»» CON… 1. Soft palate: -Pulled upward, close the -posterior nares → -Prevent reflux of food → Nasal cavities 2. Palatopharyngeal folds - Pulled medially, approximate each other → a sagittal slit -Performs a selective action → allowing food that masticated sufficiently to pass with ease 3. CON… A o Larynx Pulled upward & o Vocal cords of the larynx anteriorly by the neck Strongly muscles enlarges approximated the opening to the esophagus B o Epiglottis All these effects prevent passage of food → Swing backward over nose &trachea or → the opening of the Strangulation C larynx Con… 4. Upper 3 to 4 cm of the esophageal muscular wall ≡ upper esophageal sphincter ≡ pharyngoesophageal sphincter → relaxes Between swallows: - Sphincter remains strongly contracted → preventing air from entering → esophagus during respiration 11/19/2024 20 CON… 5. Then the entire muscular wall of the pharynx contracts - → Propels the food by peristalsis → esophagus  3. Esophageal Stage Two Types of peristaltic movements: 1. Primary peristalsis: Continuation of peristaltic wave that begins in pharynx → esophagus during pharyngeal stage Pharynx → stomach (8 to 10 s) In upright position, more rapid (5 to 8 sec) - gravity 11/19/2024 22 2. Secondary peristaltic waves If primary peristaltic wave fails to move → stomach all the food that entered the esophagus Distention of the esophagus by retained food → Secondary peristaltic waves Continue until all food → Emptied → stomach Initiated: - Partly by myenteric NS - Partly by reflexes that begin in pharynx → vagus → medulla → fibers → esophagus CON…. If vagus nerves are cut ? Myenteric plexus of the esophagus → excitable ( after several days) → Secondary peristaltic waves After paralysis of the brain stem swallowing reflex, food fed by tube → esophagus → stomach 11/19/2024 24 1 Storage of large quantities of food Motor Functions until the food of the Stomach processed in stomach/duodenum/ lower IT Mixing of food 2 with gastric secretions → a semifluid mixture Slow emptying (chyme ) of chyme → 3 small intestine Intestinal tract: IT  Retropulsion Food in the stomach → weak peristaltic constrictor waves (mixing waves) Begin in the mid-to upper portions of the stomach wall & move → antrum Initiated by “slow waves” = BER (3/min) As the constrictor waves progress → more intense → powerful peristaltic contractions → Constrictor rings force the antral contents under higher P → pylorus = Propulsion Basic electrical rhythm: BER, Pressure: P CON… Pylorus opening is small→ only a few ml of antral contents expelled →» duodenum with each peristaltic wave Peristaltic wave contracts the pyloric muscle → ↑ impedes emptying through it 11/19/2024 27 CON… So most of the antral contents are squeezed upstream through the peristaltic ring toward → body of the stomach Important mixing The moving peristaltic constrictive ring + mechanism upstream squeezing action = Retropulsion  Consequences of Pyloric Spasm Pyloric Spasm: Is a condition of ↑ tonicity of the pylorus Consequences: 1. Stay of food for long time in the stomach & ↑ its acidity 2. Vomiting of acidic contents 3. Pain 11/19/2024 29  Motility of the Small Intestine 1. Mixing Contractions (Segmentation) Stretching of the wall with chyme →localized concentric contractions spaced at intervals along the intestine As one set of contractions relaxes, a new set often begins, at new points between the previous ones 11/19/2024 30 CON… Its frequency is determined by the frequency of the slow waves (BER), 12/min in duodenum, 8 or 9/min in ileum Also propel the food down the intestine 11/19/2024 31  2. Propulsive Movements ( Peristalsis ) Functions: A. Progression of chyme → ileocecal valve (slow movement) B. Spread out the chyme along the intestinal mucosa Peristaltic activity ↑ after a meal due to : 1.Stretching of the duodenal wall (chyme) 2.Gastroenteric reflex: By myenteric plexus from the stomach (nervous) Gastroileal reflex: Intensifies peristalsis in the ileum 11/19/2024 32  Hormones ↑ intestinal motility Hormones Inhibit intestinal motility Gastrin Secretin CCK Glucagon Insulin Motilin Serotonin  Postprandial & interdigestive motility patterns (Stomach & Small Intestine) Motilin: Secreted by the stomach & upper duodenum Hormone Motilin during fasting → ↑ GIT motility Stimuli for Fat Secretion Acid Released cyclically → stimulates waves of GI Nervous motility = Interdigestive myoelectric complexes Site of M cells of the Secretion duodenum & Jejunum Move through the stomach & small intestine every 90 min in a fasted person Actions Stimulates Gastric & Intestinal Its secretion is inhibited after ingestion motility 11/19/2024 Gastrointestinal: GI 34  Main Functions of the large intestine 1. Absorption of water& electrolytes from chyme → solid feces (Proximal Half ) 2. Storage of fecal matter until → expelled (Distal Half) 11/19/2024 35 1. Mixing Movement - Haustrations 2.5 cms of circular muscle contracts Simultaneously, longitudinal muscle (teniae coli) contracts Combined contractions → unstimulated portion of large intestine → bulge outward into baglike sacs (haustrations) After few mins another one ( occurs continuously) Fecal material gradually exposed to mucosa → fluid & dissolved substances are progressively absorbed → 80 to 200 mL of feces /day Has a minor propulsive role 11/19/2024 36 2. Propulsive Movements - Mass Movements Modified type of peristalsis A constrictive ring in response to a distended or irritated point in the colon Rapidly, portion of colon distal to the constrictive ring (20 cm or ↑) lose haustrations &contract as a unit Propelling the fecal material en masse down the colon Relaxation occurs during the next 2 to 3 min Then, another mass movement occurs 1 to 3 times/day 11/19/2024 37 CON… When they have forced a mass of feces → rectum, the desire for defecation is felt Gastrocolic & duodenocolic reflexes facilitate it Transmitted by the autonomic NS Irritation: Initiate intense mass movements Ulcerative colitis → persist mass movements 11/19/2024 38