How is glycogen metabolism regulated in liver and muscle?

Glycogen metabolism is reciprocally regulated so synthesis and degradation don't occur simultaneously. Glycogen synthase (synthesis) is active when dephosphorylated; glycogen phosphorylase (degradation) is active when phosphorylated. Hormonal regulation differs by tissue. In liver: glucagon activates adenylyl cyclase, increasing cAMP and activating PKA, which phosphorylates and activates phosphorylase while inactivating synthase - releasing glucose for blood. Insulin reverses this. In muscle: epinephrine activates phosphorylase for local energy needs; Ca2+ from contraction also activates phosphorylase. AMP allosterically activates muscle phosphorylase during exercise. This tissue-specific regulation serves different physiological functions - liver maintains blood glucose while muscle provides local energy.