Homeostasis: explain question

In a laboratory experiment, hepatocytes (liver cells) were exposed to a very low concentration of glucagon, resulting in only a small number of glucagon molecules binding to their receptors. Despite this, a large amount of glycogen was rapidly broken down, releasing glucose into the bloodstream. Explain how the binding of a small number of glucagon molecules to receptors on hepatocytes leads to a large-scale, rapid breakdown of glycogen. Refer to the sequence of events in the cell signalling cascade, including the roles of G-protein, adenylyl cyclase, cyclic AMP (cAMP), and protein kinase A.