How are metabolic pathways regulated?

Metabolism is the sum total of all chemical reactions in the body (anabolic and catabolic). These processes are controlled by homeostasis and the negative feedback loop. For example, oxygen levels are monitored in the blood by receptors that communicate with the brain. If oxygen levels drop or become to low, the brain will send signals to the respiratory centres to adjust breathing. The individual cells of the body will respond by increasing or decreasing cellular respiration.