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Summary Learning goals case 3
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Whole case complete! Also exam questions are mentioned in the case. Thereby, also added notes during the turtorial written in red. I scored an 8 for this course.
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Learninggoals case 31. What types of energy systems do you use during exercise? (low, moderate, high-intensity)
Providing energy for contraction
Muscles store very limited reserves of ATP—4 to 6 seconds’ worth at most, just enough to get you
going. Because ATP is the only energy source used directly for contractile activities, it must be
regenerated as fast as it is broken down if contraction is to continue.
- Direct phosphorylation of ADP by creatine phosphate
Creatine phosphate (CP) is high-energy molecule, coupling CP with ADP transfers energy
and a phosphate group from CP to ADP to form ATP almost instantly. Muscle cells store
two to three times more CP than ATP. The CP-ADP reaction, catalyzed by the enzyme
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 for
maximum muscle power for about 15 seconds
- Anaerobic pathway
This pathway happens if there is no oxygen, when 70% of the contractile maximum is
reached the muscles compress the blood vessels, impairing the blood flow and oxygen
delivery. What happens to obtain energy is the breakdown of glucose from the blood or
glycogen. First glycolysis starts and glucose is broken down in pyruvic acid, this releases
small amounts of ATP (2 ATP per glucose). The pyruvate can be converted into lactic acid,
this process is called anaerobic glycolysis. Most of the lactic acid diffuses out of the
muscles into the bloodstream. Subsequently, the liver, heart, or kidney cells pick up the
lactic acid and use it as an energy source. Additionally, liver cells can reconvert it to
pyruvic acid or glucose and release it back into the bloodstream for muscle use, or
convert it to glycogen for storage. Together, stored ATP and CP and the glycolysis–lactic
acid pathway can support strenuous muscle activity for nearly a minute.
- Aerobic respiration
During rest and light to moderate exercise, even if prolonged, 95% of the ATP used for
muscle activity comes from aerobic respiration. It occurs in mitochondria and requires
oxygen. Aerobic respiration also includes glycolysis.
Glucose + oxygen carbon dioxide + water + ATP
As exercise begins, muscle glycogen provides most of the fuel. Shortly thereafter,
bloodborne glucose, pyruvic acid from glycolysis, and free fatty acids are the major
sources of fuels. After about 30 minutes, fatty acids become the major energy fuels.
Aerobic respiration provides a high yield of ATP (about 32 ATP per glucose), but it is slow
because of its many steps and it requires continuous delivery of oxygen and nutrient
fuels to keep it going.
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