How do fatigued human muscle cells repay an oxygen debt?
In the absence of oxygen, muscle cells will under go lactic acid fermentation. They make lactate from pyruvate instead of sending it into the TCA cycle. Then the lactate gets shipped to the liver, where it is turned back into pyruvate and then glucose. The liver then ships the glucose back to the muscle. Muscle lacks a few enzymes in the gluconeogenic pathway, and so you need the liver to help out. That’s the Cori cycle. I’m not really sure what you mean by oxygen debt. It’s not like it borrows oxygen and then has to give it back. If oxygen is available, the muscle gets it. If there’s not enough O2 around, then it has to make do without, and you get a cramp from all the lactate that builds up in the muscle.
