生理学的概念及生命活动的特征 (4).ppt

PhysiologyY O U C A N C L I C K H E R E T O A D D Y O U R T E X TActive TransportActive Transportn When a cell membrane moves molecules or ions uphill against a concentration gradient(or uphill against an electrical or pressure gradient),the process is called active transport.Active TransportSome examplesn sodium,potassium,calcium,iron,hydrogen,chloride,iodiden urate ions,several different sugarsn most of the amino acids4Primary active transport Active transport Secondary active transport Vesicular transport51 Primary active transportPrimary active transportCharacteristics:n occurs against an electrochemical gradient(“uphill”).n requires direct input of metabolic energy in the form of adenosine triphosphate(ATP)and therefore is active.n is carrier-mediated and therefore exhibits stereospecificity,saturation,and competition.Primary active transportExamplesa.Na+,K+-ATPase(or Na+K+pump)b.Ca2+-ATPase(or Ca2+pump)c.H+,K+-ATPase(or proton pump)Na+,K+-ATPase(or Na+K+pump)Function：Na+,K+-ATPase(or Na+K+pump)in cell membranes transports Na+from intracellular to extracellular fluid and K+from extracellular to intracellular fluid;it maintains lowintracellular Na+and high intracellular K+.Postulated mechanism of the sodium-potassium pump.ADP,Adenosine diphosphate;ATP,adenosine triphosphate;Pi,phosphateion.Na+,K+-ATPase(or Na+K+pump)Characteristics:Both Na+and K+are transported against their electrochemical gradients.Energy is provided from the terminal phosphate bond of ATP.The usual stoichiometry is 3 Na+/2 K+.Specific inhibitors of Na+,K+-ATPase are the cardiac glycoside drugs ouabain and digitalis.Ca2+-ATPase(or Ca2+pump)FunctionIt transports Ca2+against an electrochemical gradient in the sarcoplasmic reticulum(SR)or cell membranesSarcoplasmic and endoplasmic reticulum Ca2+-ATPase is called SERCA.H+,K+-ATPase(or proton pump)Primary active transport of hydrogen ions is especiallyimportant at two places in the body:(1)in the gastric glands of the stomach(2)in the late distal tubules and cortical collecting ducts of the kidneys.It is inhibited by proton pump inhibitors,such as omeprazole2Secondary active transportUnder appropriate conditions,this diffusion energy of sodium can pull other substances along with the sodium through the cell membrane.Secondary active transportCharacteristics:a.The transport of two or more solutes is coupled.b.One of the solutes(usually Na+)is transported“downhill”and provides energy for the“uphill”transport of the other solute(s).Secondary active transportCharacteristics:c.Metabolic energy is not provided directly,but indirectly from the Na+gradient that is maintained across cell membranes.Thus,inhibition of Na+,K+-ATPase will decrease transport of Na+out of the cell,decrease the transmembrane Na+gradient,and eventually inhibit secondary active transport.Secondary active transportCharacteristics:d.If the solutes move in the same direction across the cell membrane,it is called cotransport,or symport.Secondary active transportExamples:n Na+glucose cotransport in the small intestine n Na+K+2Cl cotransport in the renal thick ascending limb.Secondary active transportNa+glucose cotransport(symport)in intestinal or proximal tubule epithelial cell.Characteristics:e.If the solutes move in opposite directions across the cell membranes,it is called countertransport,exchange,or antiport.Secondary active transportExamples:n Na+Ca2+exchange n Na+H+exchangeSecondary active transportNa+Ca+countertransport(antiport).3Vesicular transportVesicular transportFunction:Transport macromolecules and particulate matterClassification:nExocytosis nEndocytosis细Thank you