1. Digestive Physiology Digestive Physiology Introduction, anatomophysiology & functional structure of the digestive system By: M.H.Dashti Lecture 1

2. Digestive System: Overview Digestive System: Overview The alimentary canal or gastrointestinal tract (GIT) consists of : –Main digestive organs: mouth, pharynx, esophagus, stomach, small intestine, and large intestine –Accessory digestive organs : teeth, tongue, salivary glands, liver, gallbladder and pancreas

3. Layers of the GI Tract Layers of the GI Tract 1. Mucosal layer 2. Submucosal layer 3. Muscularis layer 4. Serosa layer

4. Mucosa Mucosa Epithelium –stratified squamous in mouth,pharynx,esophagus & anus _ simple columnar in the rest  Structural  Digestive – contain enzyme on apical surface  Absorptive  Secretory-Exocrine,Paracrine,Endocrine Lamina propria –thin layer of loose connective tissue –contains Blood and Lymphatic Vessel's & nerves Muscularis mucosae ---thin layer of longitudinal smooth muscle – formation intestinal folds –Replace UWL with “new” nutrients: increasing digestion & absorption

5. Increase in epithelial surface area Increase in epithelial surface area Circular folds or valvula connlvents (~cm) – 3x  surface area Villi (~mm) –20x  surface area Microvilli (~nic) –100x  surface area

6. Structure of villi & Microvilli Structure of villi & Microvilli Tigth junction Interstitial fluid

7. Submucosa Submucosa Loose connective tissue containing : –B–BV, glands and lymphatic tissue –I–Intrinsic nerve plexus-- Meissner’s or sub mucosal plexus –E–Extrinsic nerve supply  Parasympathetic & sympathetic innervations –V–Vasoconstriction –m–mucosal movement

8. Muscularis Externa Muscularis Externa Skeletal muscle = voluntary control –in mouth, pharynx, upper esophagus and anus –control over swallowing and defecation Smooth muscle = involuntary control –inner circular fibers & outer longitudinal fibers –mixes, crushes & propels food along GIT

9. Activity of single unit smooth muscles in GIT Activity of single unit smooth muscles in GIT

10. Serosa Serosa An example of a serous membrane Covers all organs and walls of cavities not open to the outside of the body Secretes slippery fluid Consists of connective tissue covered with simple squamous epithelium

11. Enteric nervous system (little brain) Enteric nervous system (little brain) sub mucosal or Meissner’s plexus Myenteric or Auerbach’s plexus –Produce Reflex Arches  Sensors (stretch,chemo or osmo receptors)  Afferent neurons  Integrating center  Efferent neurons  Effectors( smooth muscle or epithelial cells) ENS

12. Central Nervous system sympathetic ganglion Vagal nuclei spinal cord Myenteric plexus Meissner’s plexus smooth muscle cells Secretory cells Endocrine cells Blood vessel's pelvic nerves Vagal nerves preganglionic fibers postganglionic fibers Enteric Nervous System Extrinsic Neuronal Pathways To GIT Vagal nuclei spinal cord Central Nervous system preganglionic fibers

13. Neural Control of GI Functions Neural Control of GI Functions Pre,v,g Sensory receptor stimuli ENS EFECTOR Short / Prevertebral Reflex Long / Central Reflex CNS Sensory receptor stimuli ENS EFECTOR Sensory receptor stimuli ENS EFECTOR Local / Enteric Reflex

14. FunctionsDigestive System: Functions of the Digestive System : F FF Functions of the D DD Digestive System : :: : Ingestion of water,nutrients,vitamins & electrolytes Transport (propulsion) via GI motility Digestion: breaking large molecules to small molecules from mouth to anus –mechanical_ via GI motility –Chemical – by GIT secretion –Bacterial_ by GIT flora storage Absorption movement from GIT into the blood stream excretion and defecation

15. Major activities of GIT Motility –Propulsive –Mixing (segmental) Secretion –Exocrine –Paracrine –Endocrine

16. Segmental movement Segmental movement

17. Propulsive movement Propulsive movement

18. Peristaltic Movement mechanism lumen Stretch Receptor bolus Direction of propulsion Muscularis externa Myenteric plexus Contraction by Sp/Ach S.L.A relaxation L.L.A contraction NO/VIP/ATP SP/5HT Aboral oral

19. Exocrine Secretion of Water and Electrolytes Exocrine Secretion of Water and Electrolytes Na + K+K+ Cl - Na + K+K+ Cl - Na + H2OH2O LUMENLUMEN Enterocyte Tight Junction K+K+

20. Exocrine Secretion of Proteins Exocrine Secretion of Proteins