Glycogenolysis is the breakdown of glycogen — the body’s stored glucose — back into glucose when blood sugar falls or muscles need fuel. Triggered by glucagon and adrenaline, the enzyme glycogen phosphorylase clips glucose units off the branched glycogen chains. In the liver, the freed glucose enters the blood to feed the brain and other tissues between meals; in muscle, it is burned on the spot for contraction (muscle lacks the enzyme to release it into blood). Along with gluconeogenesis, glycogenolysis defends the body against hypoglycaemia during fasting, exercise, and overnight — the reason the liver’s glycogen store is often called the body’s glucose buffer.