Glucagon is a hormone containing 29 amino acids secreted by pancreatic alpha cells. Its main function is to increase blood sugar levels by promoting the decomposition of liver glycogen and gluconeogenesis. It has the opposite effect of insulin, helping to maintain blood sugar stability, promoting the decomposition of fat, and enhancing liver function. Glucagon activates phosphorylase in liver cells through the cAMP-PK system, accelerates the decomposition of glycogen, and promotes the oxidation of fatty acids, thereby increasing the production of ketone bodies.