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The Digestive System.docx

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Anatomy and Physiology
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The Digestive System Alimentary Canal GI tractContinuous muscular tube that winds through the body frommouth to anusIt digest food breaks it down into smaller fragments then absorbs the digested fragments through its lining into the blood OrgansoMouthoPharynxoEsophagus oStomach oSmall intestineoLarge intestineIn a cadaver the alimentary canal is approximately 9m long but shorter in a living person because of the muscle toneAccessory Digestive OrgansOrgansoTeeth oTongueoGallbladderoSalivary glandoLiveroPancreasProduce secretions that help break down foodstuffsFood Processing Ingestion oSimply taking in food Propulsion oMoves food though the alimentary canal oPeristalsis major means of propulsion involves alternate waves of contraction and relaxation of muscles in the organ walls Its main effect is to squeeze food along the tract but some mixing occurs as wellMechanical digestionoPhysically prepares food from chemical digestion by enzymesoIncludes chewing mixing of food with saliva churning food in the stomach and segmentationlocal constrictions of the small intestine that mix food with digestive juices increasing the efficiency of absorptionChemical digestion oSeries of catabolic steps in which complex food molecules are broken down to their chemical building blocks by enzymes secreted into the lumen of the alimentary canalAbsorptionoThe passage of digested end products from the lumen of the GI tract through the mucosal cells by active or passive transport into the blood or lymph DefecationoEliminates indigestible substancesAdditional GI FunctionsNutrient production oSynthesis of vitamins by bacteria that lives in the intestine Ex Vitamin K biotin one of vitamins BProduction of neurotransmittershormones and hormonelike compounds oEx Gastrin ghrelin cholecystokinin secretin VIP etcBasic Functional Concepts The digestive system creates an optimal environment for its functioning in the lumen of the GI tract an area that is actually outside the body and essentially all digestive tract regulatory mechanisms act to control luminal conditions so that digestion and absorption can occur there as effectively as possibleDigestive activity is provoked by a range of mechanical and chemical stimulimechanoreceptors and chemoreceptorso Sensors involved in controls of GI tract activity are located in the walls of the tract organs oThey respond to several stimuli stretching the organ by food in the lumen osmolaritypH of the contentspresence of substrates and end products of digestionControls of digestive activity are both intrinsic and extrinsic oBetween the muscle layers in the wall of the alimentary canal is the gut brain consisting of enteric nerve plexuses which spread like chicken wire along the entire length of the GI tract and influence each other both in the same and in different digestive organs oThere are two kinds of reflex activity Shortmediated entirely by the local enteric plexuses in response to stimuli arising inside or outside the GI tract Longinitiated by stimuli arising inside or outside the GI tract and involve CNS centers and extrinsic autonomic nervesRelationship of the Digestive Organs to the PeritoneumPeritoneum serous membrane lines the abdominopelvic cavity Visceral peritoneumoCovers the external surfaces of most digestive organs Parietal peritoneumoLines the body wall Peritoneal cavityoA slitlike potential space containing a slippery fluid secreted by the serous membranes that lubricates the mobile digestive organs allowing them to glide across one another Mesentery a double layer peritoneum that extends to the digestive organs from the body wall dorsal and attaches to the posterior abdominal wallProvide routes for blood vessels lymphatics and nerves to reach the digestive viscera Holds organs in placeStores fatRetroperitoneal organs organs that lie posterior to the peritoneum and arent suspended by mesentery
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