Glycogenolysis
The breakdown of glycogen (stored glucose) in the liver and muscles to release glucose into the bloodstream. Glucagon stimulates hepatic glycogenolysis as part of the body's counter-regulatory response to low blood sugar. Synthetic glucagon exploits this mechanism for emergency hypoglycaemia treatment.
Technical Context
Hepatic glycogenolysis: glycogen phosphorylase cleaves glucose-1-phosphate from glycogen → conversion to glucose-6-phosphate → glucose-6-phosphatase releases free glucose into blood. The liver stores approximately 100g of glycogen (sufficient for 12-18 hours of fasting). Regulation: glucagon activates glycogen phosphorylase via cAMP/PKA (stimulating glycogenolysis) and inactivates glycogen synthase (inhibiting glycogen synthesis) — these coordinated effects mobilise stored glucose. Insulin has the opposite effects. Glucagon emergency treatment for hypoglycaemia exploits glycogenolysis: 1mg glucagon IM/SC/IV mobilises hepatic glycogen stores, raising blood glucose within 10-15 minutes. Glucagon is less effective in: glycogen-depleted states (starvation, chronic alcohol use, advanced liver disease), adrenal insufficiency, and chronic hypoglycaemia (depleted glycogen reserves).