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Gastrointestinal Physiology.docx

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Physiology 3120
Tom Stavraky

GASTROINTESTINAL PHYSIOLOGYIntroduction and AnatomyFour Digestion Processes1DigestionChemical and mechanicalSome monosaccharides digested chemically to carbs2AbsorptionFrom GI lumen to bodyGI tractmouth to rectumWant monosaccharides but not microbes3MotilityStirs and drives contentsBetter coverage and digestion with enzymesWant to make space for next meal4SecretionIn 2 directionsEnzymes water acid and mucus in GIExocrineoMostly from single layer of GI tract cellsoAlso from glands and other accessory organsEndocrine secrete into blood via vesselsExcretions of fibre some reabsorbed dead cells and bacteria from large intestineLabelAccessory glands dont come in contact with G tract but affect processingoEg salivary glandsLiver gall bladder and pancreas feed into small intestineMost digestion and absorptionsmall intestineAppendix deals with bacteria repopulationGeneral Layers of GI TractAlmost homogenous throughoutMucosa innermost layer facing lumenoMucus membrane with enterocytes not all the same various function absorptive cellsoLamina propria connective tissue layer very thin with small blood and lymphatic vesselsoMuscularis mucosae thin layer with smooth muscle contracts and relaxes for folding and motilitySubmucosa thicker layer of connective tissue bigger bloodlymph vesselsMuscularis externa major smooth muscle oContract circular muscledecrease diameteroContract longitudinalshorter tractoCoordinate to change GI tractSerosa outer connective tissue fibrous and more mechanicaloLayer secretes fluid outwards to GI to slide itself by other organs lubricationoContinuous with mesentery thin tissue connecting all organsoAlso has lymph tissue to protect from microbesEnteric Nervous SystemSubmucosal plexus and myenteric plexuso In submucosa and muscularis external layer respectively As many neurons in GI as spinal cordInnervation of PNS and SNS but ENS can function independentlyFunctions of ENSMotility controloInnervates circular and longitudinal musclesLocal blood flow regulationoEnteric controls vasodilation blood takes stuff awayGastic and pancreatic secretion regulationoEg acid in stomachEndocrine cell secretion in GI tract regulationoAlong tract secrete hormones and regulate releaseEnteroenteric reflexesoFood in stomach tells small intestine to start secreting hormonesDefense reactionsoVomiting or diarrheaInteractions with CNSoFull starving paindiscomfortoosmolarity in stomachShort and Long Reflexes of ENSStimulus food H2Ofood contributes ionsgut to brain goes to CNS via synapses long reflex pathwayCNS and autonomic nervous systemENS lots of neurons in GI wallEffector cells pancreas is part of pathwayShort reflex pathway sensory neuron in submucosal plexus innervates itself or next layeroSmooth muscle contraction and secretions
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