GI Physiology Dr. Mard, Ph.D Physiologist

1. GI Physiology Dr. Mard, Ph.D Physiologist

2. Definition of food: Definition of Complex and simple food Complete food : complex food + trace elements Duty of GI : Complex simple food Removal fat from diet Death

4. GI system composed of: Length of GI tubes:

5. Physiologic Anatomy of the GI wall • Mucosa • 2. Submucosa ( connective tissue, contain : bood & lymphatic vessels, GI glands , submucosal plexus) • 3. Muscularis (Gap J. ) : skeletal M. (voluntary) & smooth M. (involuntary) • 4. Serosa (visceral peritoneum) • Mucosa composed of : • Epithelium (renewal each 5-7 days, exocrine : secrets mucus, entroendocrine : secretes hormones to boodsream such as : Gastrin) • 2. Lamina propria (connective tissue & MALT :contains immune system cells that protect against disease : tonsils, small & intestine, appendix.) • 3. A thin layer of smooth muscle (formation the intestinal folds & villi increases the surface of absorption area )

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10. Physical basis for smooth muscle contraction: • Lack of arrangement beetween actin and myosin • 2. Actin attached to dense bodies (instead of Z disc) • 3. Some dense bodies are attached to the cell membrane • 4. Some dense bodies of djacent cells are bonded together by inercellular • protein bridges ( Gap J) • 5. Through these bonds the force of contraction is transmitted from one cell to the next

12. Cause of slowness of smooth muscle contraction: Molecular process of contraction: Differences beetween the contraction in smooth M. and striated (skeletal) M. :

13. Electrical properties of GI smooth M. : • RMP = - 56 mv • Depolarization (RMP > - 40 mv) • 3. B.E.R (basal electrical rhythm or Slow W.) and • Spike potentials • 1. Slow waves: • Definition: • Cause of generation: • Origin : cajal • Area of generation : • Ferequence: (influenced by ANS & some hormones) • Functions: • Location : • 2. Spike P. :

14. Cajal cell : in the stomach & small intestine, these cells are located in the outer circular muscle layer near the myentric plexus; in the colon, they are at the submucosal border of the circular muscle layer.

15. 2. Spike potentials : real action potential (RMP > -40 mv) Depolarition phase : caused byinward Ca++ & maybe Na+ Repolarization phase : caused byoutward K+ 3. Tonic contraction (sustained contraction) : repeated AP, some hormones… . Stimulant & inibitant GI Smooth muscle :

16. such as : fundus

19. Neural innervation of the GI tract • Enteric nervous system (extensive, well developed & • cab be independent) • Auerbachs (myentric) : controls GI movement • Located beetween GI muscular layers ? Acts generally • Meisner (submucosal plexus) : controls GI secretions • and local blood flow. • Lies in the submucosa ? Acts locally

20. 2. ANS (Autonomic nervous system) : Sympathetic (T8 – L2) Parasympathetic ( Vagus nerve and S2-S4) Role of ANS & CNS in GI 1. Conrols the GI vessels 2. Increases the speed of GI function 3. Generates harmony between GI system and other systems 4. Generates harmony between different part of the GI system 5. Ready GI system to receive food 3. GI sensory nervous system ( GIreflex pathways) : Chemoreceptor, Osmoreceptor & Mechanoreceptor . Synapse with ENS, ANS & CNS. Soma located in the vagal or dorsal root of spinal ganglia ( pain & fullness)

26. GI reflexes • Definition :A reflex is a fast, automatic, unplanned sequence of actions that occurs in response to a particular stimulus. • Integrated entirely within the gut wall ENS : GI secretions, peristalsis, mixing contractions, local inhibitory effects & so forth. • 2. Integrated by sympathetic ganglia : such as signals from the stomach to cause evacuation of the colon (gastrocolic R.) or enterogastric or colonoileal R. • 3. Integrated by spinal cord or brain stem : such as excitatory or inhibitory vago-vagal R. , Pain or defecation R.

27. Types of neurotransmitters secreted by Enteric neurons Ach , NE, ATP, Serotonin, Dopamine, CCK - PZ, Substance P, VIP, Somatostatin, met - & leu – ekephalin, and bombesin.

29. Hormonal control of GI motility • GI hormones mainly control the secretions > movement • Gastrin (14, 17 : 2-3 min, and 34 : 15 min) • G cells (antrum) • secrets in response to distention, GRP & protein products, Vagus nerve • Functions: • Stimulate gastric acid & pepsin secretion • Stimulate insulin secretion (only after a protein meal) • Stimulate gastric motility • increases the strength of antral contraction or antral systole) & • increases constriction of the pyloric sphincter • diminishing the rate of gastric empyting

30. Cck - PZ : I Cell (t1/2 = 5 min, 8, 12, 33, 39 & 58) In response to digested products of fat, fatty acid and monoglyceride Functions : contraction the gallbladder stimulate the enzymatic secretion of pancreas regulation of food intake inhibits gastric empyting increases the secretion of enterokinase enhance the motility of the small intestine & colon contraction of the pyloric sphincter (prevents the reflux of duodenal contents into the stomach) Secretin t1/2 : 5 min (S cells, in response to acidic (H) gastric juicepromotes pancreatic secretion of HCO3

31. GIP (42 a.a, duodenum & jejunum) (K cell, to fatty acid, aa, carbohydrates) Functions : 1. weak inhibitory effect on gastric motility 2. Stimulate insulin secretion Motilin22 a.a., M cell Stomach, small intestine, & colon during fasting, 100 min phases, increase GI motility) Somatostatin (14 & 28 a.a.) an inhibitory hormone: ( stomach & intestine by D cell) inhibition of GI movement inhibition of GI secretion inhibition of absorption Inhibits pancreatic exocrine secretion, gastric acid secretion, gallbladder contraction Inhition of gastric secretion produced by Acid

32. باز کیموس با تکانهبا اسیدهای فراوانمیخورد بر بام روده • یادم آرد سکرتین راهورمون خنثی کنندهحافظ و هضم کننده • میشود از s ترشحیک ببندد بیش پیلوردو کُنَد کم "هاش" معدهاصل کاری پانکراسهمیفرستد "هاش سی او سه" • "سی سی کی " چون تیر برانحل نماید چربی ها را در دئودنوم و ژژونوم"‏ I " بسازد CCK را • پس با کار اینتروگاسترونهر غذایی میشود هضم میشود هضم

33. GI blood flow • Anatomy : Inferior & superior mesenteric artery supply • intestinal blood flow; the stomach supplied by celiac artery • Regulation of the GI blood flow : • 1. Metabolic effect during feeding • 2. Cck – PZ, VIP, Gastrin & secretin increase GI blood flow; • Kinins such as kalidin & bradykinin increase GI BF • O2 Adenosine release ( as a vasodilator substance) • 4. Neuronal control of GI blood flow : ANS

35. Types of movement in GI : 1. Propulsive (peristaltic) 2. Mixing (peristaltic and local intermittent constrictive contractions : segmentation or haustration contraction)

36. Peristaltism (Peri : around , -staltis : constriction): Definition : Direction : Stimli : local stretch, physical or chemical irritation (distention of the gut, physical & chemical irritaion of the epithelial lining in the gut) Speed : Necessary neural plexus : Types : (primary and secondary) Neurotransmitters : Ach and P substance (contraction ), ATP and NO and VIP) Mechanism : local stretch serotonin signal to ENS Excitatory & inhibitory response to muscular layer

40. Chewing (mastication) : Definition : Is a voluntary – reflexive phenomenoun controlled by CNS Mechanisms : Functions : mechanical digestion mixing ( food stuff with saliva) digestion the cellulose membrane

42. Bolus beetween teeth activation T receptor Affernt nerve (5, 7 & 9) Chewing center Contraction (Digastric & Lateral ptrigoid M.) & relaxation ( Maseter, temporalis & medial ptrigoid M.) Opening the mandibular

43. Swallowing (Deglutition) • Definition : • Preswallowing process : • Oral (voluntary ) • 2. Pharyngeal (unvoluntary) • 3. Esophageal (unvoluntary) • UES : • LES :

44. Activation the mechanoreceptor in pharynx, tonsils & tongue afferent nerve (9 & 10) Swallowing center ( NTS & DMV) Efferent nerve (5, 7 & 12) Inhibitory signal to 1. UES, 2. LES, 3. Respiratory center 4. gastric fundus Excitatory signal to 1. soft palate ( uvula), 2. Larynx ( approximation of vocal cord) 3. The Epiglotis closes off the opening to the larynx) 4. Contraction the muscles of pharynx

47. Esophagus Function : Movement : Secretion : UES : LES :

48. UES and LES What is importance of esophageal sphincters? -The esophagus is situated within the pressure thorax and the presence of these sphincters is important to prevent the entry of air and gastric contents In infants? Colic pain? Esophageal innervation The esophagus is richly supplied with enteric neurons. Functions of esophageal neurons are • Sensing the presence of food 2. Sensing the nature of contents

49. Esophageal motility pattern Type of peristalsis Primary Secondary (importance) -occurs when a bolus trapped in the esophagus and primary peristalsis fails to move downward it. -Strength of peristaltic wave is determined by size of bolus -Excess distention inhibit contractions The nature of bolus influences the intensity of the esophageal motility pattern 1. Larger and more viscous boluses are propelled with greater force 2. Warm boluses are moved more rapidly than cold ones.

50. Different responses of peristaltic movements of distal part of esophagus to acid or air 1.The presence of acid alone without significant distention elicits secondary peristaltic wave 2.The presence of air elicits retrograde movements, belching.