Y khoa, dược - Chapter 3: The human body: from food to fuel

Chapter 3 The Human Body: From Food to FuelTaste and Smell: The Beginnings of Our Food ExperienceSight, smell, thought, taste, and soundTrigger a set of responses that prepare the digestive tract to receive foodThe Gastrointestinal TractVariety of functions, including:Ingestion of foodTransport of ingested foodSecretion of digestive enzymes, acid, mucus, and bileAbsorption of end products of digestionMovement of undigested materialElimination of digestive waste productsThe Gastrointestinal TractSeveral layers to the GI tract, includingMucosaCircular muscleLongitudinal muscleSphinctersOverview of DigestionPhysical movementPeristalsisWavelike, muscular contractionsTransport food and nutrients along the GI tractSegmentationSeries of muscular contractions in the small intestinesDivides and mixes the chymeChemical breakdownEnzymesProteins that catalyze chemical reactionsOther secretionsAcidBaseBileMucusOverview of DigestionOverview of AbsorptionThe road to nutrition absorptionPassive diffusionFacilitated diffusionActive transportAssisting OrgansSalivary glandsMoisten foodSupply enzymesAssisting OrgansLiverProduces bile“Chemical factory”“Dynamic warehouse”Assisting OrgansGallbladderStores and secretes bilePancreasSecretes bicarbonateSecretes digestive enzymesPutting it All Together: Digestion and AbsorptionMouthEnzymesSalivary amylase acts on starchLingual lipase acts on fatSalivaMoistens food for swallowingPutting it All Together: Digestion and AbsorptionEsophagusTransports food to stomachEsophageal sphincterPutting it All Together: Digestion and AbsorptionStomachHydrochloric acid prepares protein for digestion and activates enzymesPepsin begins protein digestionGastric lipase has some fat digestionGastrin (hormone) stimulates gastric secretion and movementIntrinsic factor is needed for absorption of vitamin B12Putting it All Together: Digestion and AbsorptionSmall intestineSections of small intestineDuodenum, jejunum, and ileumNutrient digestionBicarbonate neutralizes stomach acidPancreatic and intestinal enzymesCarbohydratesFatProteinPutting it All Together: Digestion and AbsorptionSmall intestineAbsorptionFolds, villi, and microvilli expand absorptive surfaceMost nutrients absorbed hereFat-soluble nutrients go into lymphOther nutrients go into bloodPutting it All Together: Digestion and AbsorptionLarge intestineSectionsCecum, colon, rectum, anal canalDigestion Peristaltic movement is slow, taking 18–24 hours for material to travelSome digestion of fiber by bacteriaPutting it All Together: Digestion and AbsorptionLarge IntestineAbsorptionWaterSodium, potassium, and chlorideVitamin K (produced by bacteria)EliminationCirculation of NutrientsVascular systemVeins and arteriesCarries oxygen and nutrients to tissuesRemoves wastesLymphatic systemVessels that drain lymphEmpties into the bloodstream near the neckCirculation of NutrientsExcretion and eliminationLungs Excrete water and carbon dioxideKidneys filter bloodExcrete waste; maintain water and ion balanceSignaling Systems: Command, Control, and DefenseNervous systemRegulates GI activityEnteric nervous systemAutonomic nervous systemHormonal systemIncreases or decreases GI motility and secretionsInfluence your appetiteSignaling Systems: Command, Control, and DefenseImmune systemProtects us from foreign invadersRole of GI tractBarrierImmune responseNatural killer cellsMacrophagesLocation of lymphoid tissuesLymphocytesAntibodiesInfluences on Digestion and AbsorptionPsychological influencesTaste, smell, and presentation of foodChemical influencesType of protein you eat and the way it is preparedBacterial influencesHydrochloric acid kills most bacteriaNutrition and GI DisordersConstipation Hard, dry, infrequent stoolsReduced by high fiber, fluid intake, exerciseDiarrheaLoose, watery, frequent stoolsSymptom of diseases/infectionsCan cause dehydrationBroth, tea, toast, and other low-fiber foods can help reduceNutrition and GI DisordersDiverticulosisPouches along colonHigh-fiber diet reduces formationHeartburn and GERDReduced by smaller meals, less fatSmoking weakens the esophageal sphincterBeing overweight often worsens symptomsNutrition and GI DisordersIrritable bowel syndromeCauses abdominal pain, diarrhea or constipation, and crampsStress and certain foods aggravate the symptomsCan usually be controlled by diet and lifestyle modificationsStress managementNutrition and GI DisordersColorectal cancerFiber-rich diet may reduce riskGasMost foods that contain carbohydrates can causeUlcersPain in the upper abdomenCan cause nausea, vomiting, loss of appetite, and weight lossBacterial cause (H. pylori)Nutrition and GI DisordersFunctional dyspepsiaChronic pain in the upper abdomenTreat with medicine and stress reduction