讲座骨矿物质钙作用功能lecture bone minerals.pptx

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讲座骨矿物质钙作用功能lecture bone minerals.pptx

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Lecture20BoneMinerals

Calciumrolesfunctions99%storedinbonesandteethBonestructurehydroxyapatitecrystalsbuiltuponcollagenfoundationofboneOsteoblasts?newboneformation??phosphorouslevelsReplacesCa++inhydroxyapatitecrystals?boneintegrity?lossofCa++frombonestructure1%circulatinginbloodsofttissueBloodcalciumconcstrictlymaintained

RegulationofbloodCalciumLOWbloodcalcium?SecretionPTHfromparathyroidglandsActivationofVitaminD?renalreabsorption

ofCa++?Ca++releaseintoblood

frombonedemineralisation

byosteoclasts?Ca++absorption

fromSI?BloodCa++Lowdietary

Ca++intake

RegulationofbloodCalciumHIGHbloodcalcium?SecretionCalcitoninfromthyroidglandActivationofVitaminDinhibited?renalreabsorption

ofCa++?bonedemineralisation?Ca++absorption

fromSI?BloodCa++?Ca++intake

(supplementation)

CalciumrolesfunctionsCalciumfacilitatestransmissionofnerveimpulsesCa++flowsintonervecellsStimulatesneurotransmitterreleaseNeurotransmitterstransfernerveimpulsesfromoneneurontothenext??dietarycalcium?convulsionsInhibitionofnerveimpulsetransmission

CalciumrolesfunctionsCalciumfacilitatesmusclecontractionMusclerelaxed=lowIMCa++levelsMusclecontraction=?Ca++flowintomusclecellsLowdietarycalciumnmusclecontraction/relaxationinhibitedMuscletwitchingspasms(calciumtetany)ExcessdietarycalciumFailureofmusclestorelaxStiffeningofmuscles(calciumrigor)Skeletalandcardiacmusclesusceptible

OsteoporosisLowbonemassAgeing??bonefragility??riskbonefractureCommonsitesHipVertebraeGradualcompressionfracturesofuppervertebrae?kyphosis(‘Dowagershump’)?oestrogenpost-menopause?graduallossofbonemassOestrogen(testosteroneinmen)Limitactivityofosteoclasts??oestrogen??bonedemineralizationbyoesteoclasts

Osteoporosis

DietarycalciumabsorptionSitesDuodenumIleumJejunumColonabsorptionAbsorptioninverselyproportionalto‘dose’M