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NUR1 324

SUMMARY DIGESTIONGeneral information about the GITMain role in homeostasis provide appropriate amount and type of nutrients to bodyMain propertiesoTubular natureoCommunication with external environmentThe lumen is considered as being part of the external environment 2 types of evolutionary developmentoGrowthIn length the human GIT is 3x the height of an average manGrowth of the internal surface inner surface is 600x larger than the outer surface because of convolutionsRole is to increase efficiency of diffusion oDifferentiationThe GIT is not a simple structure it is a sequence of interconnected organsHowever if you take a cross section anywhere you will get the same 4 typical layers making the wall of the GIT4 layers of the gut wall from outside to lumenoSerosa thin but though layer of tissueoMuscularis externaLongitudinal layer muscles fibers parallel to the tube responsible for the shortening of the GITCircular layer muscle fibers at right angle with the long axis of the gutThey cause constriction of the GIT when they contractNote the GIT is composed of smooth muscle everywhere except in mouth pharynx upper 13 of the esophagus and anus which have striated muscleoSubmucosa loose connective tissueCharacterized by having a lot of nerves lymphatics and blood vesselsoMucosaMuscularis mucosa smooth muscleLamina propria connective tissue with immune propertiesEpithelial cells secretory and absorptive cellsGIT functionsoMotilityPropulsionPhysical breakdownContractile activity of the muscle of the GIToSecretionChemical breakdownoAbsorptionTransfer to circulationRaison dtre of the GITDigestiveabsorptive efficiencyCarbohydrates 99Fat 95Protein 92The enteric nervous systemUnique to the GITIndependent integrative nervous systemInitiates programs regulates and coordinates activities of muscular and secretory elements of the GITGut wall innervation1Purple sensory neuronsRed excitatory neurons release ACh on muscarinic receptors of the muscle and secretory cellsOrange inhibitory neurons release NANCYou also have interneurons in the plexusesWe will consider the submucosal plexus and the myenteric plexus as one functional unit All elements of a reflex arc are presentNote 1 predominant innervation to the circular muscle layer is inhibitoryNote 2 muscarinic receptors are blocked by atropineSphinctersNameAnatomyPropertiesRolesHormonal Neural regulationregulationUES upper Corresponds to the Normally closedPrevents from Closure esophageal cricopharyngeus Relaxed during entering esophagus impulses from sphinctermuscledeglutitionwhere pressure is the CNS lower than in the mediated by pharynxthe vagus releasing ACh on nicotinic receptors causing muscle contractionRelaxation cessation of impulses during deglutitionLES lower Anatomically Closure is Prevent reflux Small influence on Mall influence esophageal insignificant but myogenic it is an of gastric juice resting toneon resting tone sphincterfunctionally very intrinsic in the Note that gastrin important physiologic esophagusdoes NOT play a Relaxation Consists of lower 4 cm sphincterrole in regulating neurogenicof esophagusAssisted by the LES under Caused by Inferior 2 cm are in the presence of physiological local release of abdominal cavityintraabdominal conditions NANC by segmentEstrogen may enteric lower pressure inhibitory within the sphincter neuronsPyloric Anatomically well Very narrow Functionally sphincterdeveloped massive lumen that insignificant musclebehaves as Open at rest spincterClosed by antral peristalsisIleocecal Between SI and colonPrevents valvebacteria of colon from entering in SISpincter of At the intersection of When closed bile Control flow Oddicommon bile duct and is stored in of bile in duodenal lumen near gallbladderduodenal pancreatic ductlumen Autonomic innervationParasympatheticSympatheticSynapsesPreganglionic synapses only on Postganglionic synapses first outside of the 2
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