i dont really understand this very well may you please help me?
When Oxygen is not available, the cell is forced to produce energy (=ATP) through ANAEROBIC processes, that produce much less energy (about 15 times less), than AEROBIC processes.
Oxygen is essential for the functioning of the electron transport chain.
The electron transport chain (ETC) allows the cell to produce energy (ATP) by creating a proton gradient across the mitochondrial membrane.
The necessary steps to produce energy from glucose are:
Glycolisis --> Kreb's cycle --> ETC
During glycolisis and Kreb's cycle NAD+ is transformed in NADH. In order for this processes to continue NAD+ needs to be replaced, and the ETC is, in the presence of oxygen, able to do that.
If ETC doesn't work NAD+ is not restored and the cell needs to find another source of it.
In this case pyruvate, instead of entering in the Kreb's cycle, will be transformed in Lactate through the enzyme lactate dehydrogenase, and NAD+ will be produced:
Pyruvate + NADH ------> Lactate + NAD+
That why with hypoxia cells/tissue accumulate lactate, causing acidosis.
I hope this helped. Let me know if I answered your question.