Glycogenolysis is the catabolism of glycogen (requiring removal of glucose unit from glycogen and addition of phosphate) thus producing glucose 1-phosphate, and subsequently reconfigured (C-1 -> C-6) to yield glucose 6-phosphate, a potent reaction intermediary leading to glucose available to the blood and brain, pyruvic acid (yet another potent intermediate) or reverting to glycogen if not immediately needed, as metabolically necessary.

Glycogenolysis requires three enzymes :

• Phosphorylase
• Transferase & α-1,6-Glucosidase (bifunctional enzyme)
• Phosphoglucomutase

The liver also contains an additional enzyme, glucose 6-phosphatase, which cleaves the phosphate group to form free glucose.

Glycogenolysis transpires in the muscle and liver tissue, where glycogen is stored, as a hormonal response to epinephrine (e.g., adrenergic stimulation) and/or glucagon, a pancreatic peptide triggered by low blood glucose concentrations.

Of note, oral administration of glucagon is a common human medical intervention when intraveinous access is unavailable in diabetic emergencies.