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1、Chapter 12 Blood and the Lymphatic And Immune SystemPart I: Blood Anatomyand Physiology of BloodThe average adulthasabout5litersofblood.It circulatesthroughout the body withinthe blood vesselsofthe cardiovascular system.Bloodisa mixture ofcellsfloating in wateryplasma.Asa
2、 group these cellsare referred toasformed elements,butthere are threedifferentkinds:erythrocytesorred blood cells,leukocytesorwhite blood cells,andplatelets.Blood cellsare produced inthe red bone marrow bya processcalledhematopoiesis.Plasma and erythrocytesare responsible
3、 fortransporting substances,leukocytesprotectthe bodyfrominvading microorganismand plateletsplay a role incontrolling bleeding.PlasmaLiquid plasma composesabout 55 percentofwhole blood inthe average adultand is90 to 92 percentwater.The remaining 810 percentportionofplasma
4、 isdissolved substances,especiallyplasma proteinssuchasalbumin,globulins,andfibrinogen.Albuminhelpstransport fattysubstancesthat cannot dissolve inthe wateryplasma. There are threemain typesofglobulins.One ofthese,gamma globulins,actsasantibodies.Fibrinogenisa bloodclotti
5、ng protein.Inadditionto the plasma proteins,smaller amountsofother importantsubstancesare alsodissolved inthe plasma fortransport:calcium,potassium,sodium,glucose, amino acids,fats,and waste productssuchasureaandcreatinine.ErythrocytesErythrocytesare alsocalled red blood
6、cells(RBCs).Theyare biconcave disksand areenucleated,whichmeanstheynolonger containa nucleus.Red blood cellsappear red incolorbecause theycontainhemoglobin,whichisanironcontaining pigment.Hemoglobinisthe partofthe red blood cellthatpicksup oxygenfromthe lungsand deliversi
7、tto the tissuesofthe body.There are about5 millionerythrocytesper cubicmillimeter ofblood.The total number inanaveragesized adultis35 trillion,withmaleshaving more redbloodcellsthanfemales.Erythrocyteshave anaverage life spanof120 daysand thenthe spleen removesthe wornout
8、 and damaged onesfromcirculation.Muchofthe redbloodcell,suchasthe iron,canbe reused butone porti
