Question

The citric acid cycle is a crucial metabolic sequence found in all organisms. When is this pathway active in the muscles and liver? When is this pathway shut down in the muscles and liver?

Answer 1

With respect to energy, the liver and muscles act complementarily. The liver is the major organ in the body for the synthesis of glucose. Muscles are major users of ATP. Actively exercising muscles generate lactate as a result of running glycolysis faster than the blood can deliver oxygen during periods of heavy exercise. As a consequence, the muscles go anaerobic and produce lactate. This lactate is of no use to muscle cells, so they dump it into the blood. Lactate travels in the blood to the liver, which takes it up and reoxidizes it back to pyruvate, catalyzed by the enzyme lactate dehydrogenase. Pyruvate in the liver is then converted to glucose by gluconeogenesis. The glucose thus made by the liver is dumped into the bloodstream where it is taken up by muscles and used for energy, completing a very important intercellular pathway known as the cori cycle