glycogenolysis The conversion of glycogen to glucose, which occurs in the liver and is stimulated by glucagon from the pancreas and adrenaline from the adrenal medulla. These hormones activate an enzyme that phosphorylates glucose molecules in the glycogen chain to form glucose 1-phosphate, which is converted to glucose 6-phosphate. This is then converted to glucose by a phosphatase enzyme. In skeletal muscle glycogen is degraded to glucose 6-phosphate, which is then converted into pyruvate and used in ATP production during glycolysis and the Krebs cycle. However, pyruvate can also be converted, in the liver, to glucose; thus muscle glycogen is indirectly a source of blood glucose. Compare glycogenesis.

glycogenolysis The breakdown of glycogen to glucose for use as a metabolic fuel and to maintain the normal blood concentration of glucose in the fasting state. Stimulated by the hormones glucagon and adrenaline.

glycogenolysis (gly-koh-jĕ-nol-i-sis) n. a biochemical process, occurring chiefly in the liver and in muscle, by which glycogen is broken down into glucose.