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muscles and metabolism.doc

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Anatomy and Physiology
Jacqueline Carnegie

Muscles and MetabolismHow does the body provide the energy needed for contractionas muscles contract ATP supplies the energy fro cross bridge movement and detachment and for operation of the calcium pump in the sarcoplasmic reticulum muscles store only 4 to 6 seconds worth of ATP reserves usually just enough energy to begin movementsince ATP is the only energy source used directly for contractile activities it must be regenerated as fast as it is broken down in order for contraction to continue after ATP is hydrolyzed to ADP and inorganic phosphate in muscle fibres it is regenerated quickly by 1 or more of these pathways1 Direct phosphorylation of ADP to creatine phosphateduring vigorous activity the demand for ATP soars and the ATP stored in working muscles is consumed within a few twitchescreatine phosphateCP a unique highenergy molecule stored in muscles is used toregenerate ATP while the metabolic pathways are adjusting to the suddenly higher demands for ATPthe result of coupling CP with ADP is an almost instant transfer of energy and a phosphate group from CP to ADP to form ATP creatine phosphateADPcreatine kinase creatineADPmuscle cells store 2 to 3 times as much CP as ATP and the CPADP reaction catalyzed by creatine kinase is so efficient that the amount of ATP in muscle cells changes very little during the initial period of contraction together stored ATP and CP provide maximum muscle power for 1416 secondsthe coupled reaction is readily reversible and to keep CP readily available CP reserves are replenished during periods of rest or inactivity 2 Glycolysis an anaerobic pathway which converts glucose to lactic acidwhen stored ATP and CP become exhausted more ATP is generated by breakdown catabolism of glucose obtained from the blood or of glycogen stored in the muscle the initial phase of glucose breakdown is called glycolysis sugar splittingthis pathway occurs in both the presence and absence of oxygenit does not use oxygen so it is anaerobicduring glycolysis glucose is broken down to two pyruvic acid molecules releasing enough energy to form small amounts of ATP 2 ATP per glucose normally pyruvic acid produced during glycolysis enters the mitochondria and reacts with oxygen to produce more ATP aerobic respirationwhen muscles contract vigorously and contractile activity reaches about 70 of the maximum possible the bulging muscles compress the blood vessels within them impairing blood flow and oxygen delivery
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