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Human Physiology: The Mechanism of Body Function - part 5

góp phần phosphoryl hóa oxi hóa. 30 phút tiếp theo hoặc các nhiên liệu truyền qua máu trở nên chiếm ưu thế, đường huyết và các axit béo đóng góp xấp xỉ như nhau, ngoài thời gian này, các axit béo trở nên dần dần quan trọng hơn, và đường sử dụng giảm đi. Nếu cường độ tập thể dục vượt quá khoảng 70% tỷ lệ tối đa của ATP sự cố | Vander et al. Human Physiology The Mechanism of Body Function Eighth Edition II. Biological Control Systems 11. Muscle The McGraw-Hill Companies 2001 Muscle CHAPTER ELEVEN 313 FIGURE 11-26 The three sources of ATP production during muscle contraction 1 creatine phosphate 2 oxidative phosphorylation and 3 glycolysis. ĨÕĨ contributing to oxidative phosphorylation. For the next 30 min or so blood-borne fuels become dominant blood glucose and fatty acids contributing approximately equally beyond this period fatty acids become progressively more important and glucose utilization decreases. If the intensity of exercise exceeds about 70 percent of the maximal rate of ATP breakdown however glycolysis contributes an increasingly significant fraction of the total ATP generated by the muscle. The glycolytic pathway although producing only small quantities of ATP from each molecule of glucose metabolized can produce large quantities of ATP when enough enzymes and substrate are available and it can do so in the absence of oxygen. The glucose for glycolysis can be obtained from two sources the blood or the stores of glycogen within the contracting muscle fibers. As the intensity of muscle activity increases a greater fraction of the total ATP production is formed by anaerobic glycolysis with a corresponding increase in the production of lactic acid which dissociates to yield lactate ions and hydrogen ions . At the end of muscle activity creatine phosphate and glycogen levels in the muscle have decreased and to return a muscle fiber to its original state these energy-storing compounds must be replaced. Both processes require energy and so a muscle continues to consume increased amounts of oxygen for some time after it has ceased to contract as evidenced by the fact that one continues to breathe deeply and rapidly for a period of time immediately following intense exercise. This elevated consumption of oxygen following exercise repays what has been called the oxygen debt that is .