The provided source distinguishes between glycogenolysis in the liver and muscle, highlighting their differing metabolic outcomes. Liver glycogenolysis is unique because the liver possesses glucose-6-phosphatase, an enzyme that allows it to convert glucose-6-phosphate into free glucose, which can then be released into the bloodstream. Conversely, muscle glycogenolysis only yields glucose-6-phosphate, which is utilized internally for energy production through glycolysis as muscle tissue lacks glucose-6-phosphatase. This difference explains why the liver can contribute to maintaining blood glucose levels, while muscle energy is for its own use. The source emphasizes the liver's distinct role in glucose homeostasis due to this enzymatic presence.

The provided text from the "Metabolism Made Easy" YouTube channel explains the critical role of oxygen in the Electron Transport Chain (ETC), a vital process for cellular energy production. It highlights how hypoxia, or a lack of oxygen, significantly inhibits the ETC, thereby reducing the output of ATP, the body's primary energy currency. This reduction in ATP can severely impair the function of aerobic tissues like the brain and heart, which heavily rely on oxygen-dependent pathways for energy. The source emphasizes that multiple mitochondrial catabolic processes that produce NADH and FADH2 will not generate usable energy in the absence of sufficient oxygen, ultimately leading to tissue damage, particularly in the brain, which is highly dependent on glucose oxidation for ATP.

Around 95% of the oxygen we breathe is consumed by the electron transport chain in the mitochondria. This process is also known as cellular respiration. Its function is to oxidize the high-energy molecules produced from mitochondrial catabolism into ATP, a more usable form of energy.