7 The Muscular System

ATP and CP Reserves (7-6) At rest, muscle cells generate ATP, some of which will be held in reserve Some is used to transfer high energy to creatine forming creatine phosphate (CP) © 2013 Pearson Education, Inc.

ATP and CP Reserves (7-6) During contraction each cross-bridge breaks down ATP into ADP and a phosphate group CP is then used to recharge ATP The enzyme creatine phosphokinase (CPK or CK) regulates this reaction It lasts for about 15 seconds ATP must then be generated in a different way © 2013 Pearson Education, Inc.

Aerobic Metabolism (7-6) Occurs in the mitochondria Using ADP, oxygen, phosphate ions, and organic substrates from carbohydrates, lipids, or proteins Substrates go through the citric acid cycle A series of chemical reactions that result in energy to make ATP, water, and carbon dioxide Oxygen supply decides ATP aerobic production © 2013 Pearson Education, Inc.

Glycolysis (7-6) Breaks glucose down to pyruvate in the cytoplasm of the cell If pyruvate can go through the citric acid cycle with oxygen, it is very efficient Forming about 34 ATP With insufficient oxygen, pyruvate yields only 2 ATP Pyruvate is converted to lactic acid Potentially causing a pH problem in cells © 2013 Pearson Education, Inc.

Figure 7-9 Muscle Metabolism. Fatty acids G Blood vessels Glucose Glycogen Mitochondria Creatine Resting: Fatty acids are catabolized; the ATP produced is used to build energy reserves of ATP, CP, and glycogen. Fatty acids Glucose Glycogen 2 2 Pyruvate 34 34 To myofibrils to support muscle contraction Moderate activity: Glucose and fatty acids are catabolized; the ATP produced is used to power contraction. Lactate Glucose Glycogen 2 2 Pyruvate Creatine Lactate To myofibrils to support muscle contraction Peak activity: Most ATP is produced through glycolysis, with lactate and hydrogen ions as by-products. Mitochondrial activity (not shown) now provides only about one-third of the ATP consumed. © 2013 Pearson Education, Inc.

Figure 7-9a Muscle Metabolism. Fatty acids G Blood vessels Glucose Glycogen Mitochondria Creatine Resting: Fatty acids are catabolized; the ATP produced is used to build energy reserves of ATP, CP, and glycogen. © 2013 Pearson Education, Inc.

Figure 7-9b Muscle Metabolism. Fatty acids Glucose Glycogen 2 2 Pyruvate 34 34 To myofibrils to support muscle contraction Moderate activity: Glucose and fatty acids are catabolized; the ATP produced is used to power contraction. © 2013 Pearson Education, Inc.

Figure 7-9c Muscle Metabolism. Lactate Glucose Glycogen 2 2 Pyruvate Creatine Lactate To myofibrils to support muscle contraction Peak activity: Most ATP is produced through glycolysis, with lactate and hydrogen ions as by-products. Mitochondrial activity (not shown) now provides only about one-third of the ATP consumed. © 2013 Pearson Education, Inc.

Muscle Fatigue (7-6) Caused by depletion of energy reserves or a lowering of pH Muscle will no longer contract even if stimulated Endurance athletes, using aerobic metabolism, can draw on stored glycogen and lipids Sprinters, functioning anaerobically, deplete CP and ATP rapidly, and build up lactic acid PLAY ANIMATION Frog Fatigue © 2013 Pearson Education, Inc.

The Recovery Period (7-6) Requires "repaying" the oxygen debt by continuing to breathe faster Even after the end of exercise, and recycling lactic acid Heat production occurs during exercise Raising the body temperature Blood vessels in skin will dilate; sweat covers the skin and evaporates Promoting heat loss © 2013 Pearson Education, Inc.