CopyrightOTheMcGraw-HiliCeParotidsalivaryglandChapter 6Mouth-PharynxTracheaSublingualsalivaryglandEsophagusGastrointestinalSubmandibularsalivaryglandPhysiologyLiverStomachDai HuaGallbladder-PancreasMedical CollegeSmallintestineColonYangzhou UniversityLargeCecumintestineRectumAnus
Chapter 6 Gastrointestinal Physiology Dai Hua Medical College Yangzhou University
Gastrointestinal PhysiologySection 1IntroductionSection2Mastication and deglutitionSection3Gastric secretionSection 4Digestion in stomachSection5Digestion in small intestinesSection 6Physiology of colonSection7Absorption
Section 1 Introduction Section 2 Mastication and deglutition Section 3 Gastric secretion Section 4 Digestion in stomach Section 5 Digestion in small intestines Section 6 Physiology of colon Section 7 Absorption Gastrointestinal Physiology
copyrightoTidisplayParotidGastrointestinalSystemsalivaryglandMouthPharynxincludes Gltractplus theTracheaSublingualaccessoryorganssalivaryglandEsophagusSubmandibularsalivaryglandMany functions in the gut are foundin specificlocations along its length.LiverMost of digestion:StomachGallbladderPancreasAccomplishedintheSmallSmallIntestine.intestineColonLargeCecumintestineAbsorption:RectumAnusOccursinthesmall intestine
Many functions in the gut are found in specific locations along its length. Gastrointestinal System Most of digestion： Accomplished in the Small Intestine. Absorption： Occurs in the small intestine. — includes GI tract plus the accessory organs
ExocrineOrganFunctionssecretionsMouthandChewingbegins;initiation ofswallowing reflexPharynxSaltandwater moistenfoodSalivaryglandsAmylasePolysaccharide-digestingenzymeEsophagusMovingfoodtostomachbyperistalticwavesMucusLubricationStomachStore,mix,andcontinuedigestionoffood;regulateemptyingofdissolvedfoodintosmall intestineHCISolubilizationoffoodparticles;kill microbes;activationofpepsinogenstopepsinsPepsinogenProtein-digestingenzymesMucusLubricateandprotectepithelialsurfacePancreasSecretion ofenzymes and bicarbonate;alsohasnondigestiveendocrinefunctionsEnzymesDigestcarbohydrates,fats,proteins,andnucleicacidsBicarbonateNeutralizeHClenteringsmall intestinefromstomachLiverBilesaltsSecretionofbile;manyothernondigestivefunctionsSolubilizewater-insolublefatsBicarbonateNeutralizeHClenteringsmallintestinefromstomachOrganicwasteproductsandtracemetalsEliminationinfecesGallbladderStoreandconcentratebilebetweenmealsSmall intestineDigestionandabsorptionofmostsubstancemixingandpropulsionofcontentsEnzymesFooddigestionSalt and waterMaintainfluidity of luminal contentsMucusLubricationLargeintestineStorageandconcentrationofundigested waterabsorptionofsaltandwater,mixingandpropulsionofManyfunctionsinthegutarefoundcontents;defecationmixingandpropulsionofcontentsinspecificlocationsalongitslengthMucusLubrication
Stomach Store, mix, and continue digestion of food; regulate emptying of dissolved food into small intestine HCl Solubilization of food particles; kill microbes; activation of pepsinogens to pepsins Pepsinogen Protein-digesting enzymes Mucus Lubricate and protect epithelial surface Pancreas Secretion of enzymes and bicarbonate; also has nondigestive endocrine functions Enzymes Digest carbohydrates, fats, proteins, and nucleic acids Bicarbonate Neutralize HCl entering small intestine from stomach Liver Bile salts Secretion of bile; many other nondigestive functions Solubilize water-insoluble fats Bicarbonate Neutralize HCl entering small intestine from stomach Organic waste products and trace metals Elimination in feces Exocrine Organ secretions Functions Mouth and Chewing begins; initiation of swallowing reflex Pharynx Salt and water moisten food Salivary glands Amylase Polysaccharide-digesting enzyme Esophagus Moving food to stomach by peristaltic waves Mucus Lubrication Small intestine Digestion and absorption of most substance mixing and propulsion of contents Enzymes Food digestion Salt and water Maintain fluidity of luminal contents Mucus Lubrication Gallbladder Store and concentrate bile between meals Large intestine Storage and concentration of undigested water, absorption of salt and water, mixing and propulsion of contents; defecation mixing and propulsion of contents Mucus Lubrication Many functions in the gut are found in specific locations along its length
FourprocessescarriedoutbytheGltractCopyrightThe McGraw-Hill Companies, Inc.Permission requiredfor reproduction or display.BloodflowHeartLiverHepaticportalveinSecretionAbsorptionMouth-AnusFoodandDigestionwaterFecesEsophagusRectumSmallintestineStomachColonMotilityFunctionsofGastrointestinalSystem
Four processes carried out by the GI tract Functions of Gastrointestinal System
StructureoftheGlTractWallVeinSubmucosalplexusMesentery(plexusofMeissner)ArteryGlands insubmucosaNerveSubmucosaGlandinmucosaDuct of glandoutsidetractMyentericplexusLymphatictissueSerosa:LumenAreolarconnectivetissueEpitheliumMucosa:Muscularis:EpitheliumLaminapropriaCircularmuscleMuscularismucosaeLongitudinalmuscleFromthe mid-esophagus totheanus,thewall oftheGltracthasthegeneralstructure,included inthe epithelial layerare exocrine /endocrine cells
Structure of the GI Tract Wall From the mid-esophagus to the anus, the wall of the GI tract has the general structure, included in the epithelial layer are exocrine /endocrine cells
I. Physiological properties of gastrointestinalsmooth muscle(1)GeneralpropertiesCARDIACSKELETAL- Low excitabilitySMOOTH-High extensibilityTYPESOFMUSCLETISSUEToniccontractionwww.visiblebody.com-Autorhythmicity- High sensitivity to temperature, stretch &chemicalstimulation,but not electric stimulus
– High sensitivity to temperature, stretch & chemical stimulation, but not electric stimulus. I. Physiological properties of gastrointestinal smooth muscle (1) General properties – Low excitability – High extensibility – Tonic contraction – Autorhythmicity
Tonic contractions_ Tonic contractions are continuous instead of rhythmicaland last several minutes-to-hours- They are caused by:-Repetitive spikes- Continuous depolarization- Continuous entry of Ca?+
– Tonic contractions are continuous instead of rhythmical and last several minutes-to-hours. Tonic contractions – They are caused by: - Repetitive spikes - Continuous depolarization - Continuous entry of Ca2+
(2)Electrophysiologicalproperties(a) Resting potential:-Between-50~-60mV-lonicbasisEm (selective membrane permeability to KtNa+- K+ pump, K+, Cl, Ca2+o60Tension
– Ionic basis Em (selective membrane permeability to K+ ) Na+ - K+ pump, K+ , Cl- , Ca2+ (2) Electrophysiological properties (a) Resting potential: – Between - 50 ~ - 60 mV
(b) Slow wave (basic electrical rhythm, BER)- The spontaneous rhythmic, sub-thresholddepolarization of the cell membrane(slow wave) of the G.l. tractActionpotentialsae-Initiatedintheinterstitialcells of Cajal (ICC)Threshold(pacemakercell)60SlowwavesTime (sec)MechanicalthresholdChemicalthresholdTime (sec) 2011 Pearson Education, Inc
– The spontaneous rhythmic, sub-threshold depolarization of the cell membrane (slow wave) of the G.I. tract (b) Slow wave (basic electrical rhythm, BER) – Initiated in the interstitial cells of Cajal (ICC) (pacemaker cell) Mechanical threshold Chemical threshold