In pancreatic islets, alpha or A-cells constitute about $15 \%$ of pancreatic islets cells and secrete glucagon. Its molecule consists of a single polypeptide chain of 29 amino acid residues. Glucagon intensifies glycogenolysis, deamination and gluconeogenesis, and inhibits glycogenesis in liver cells. It also intensifies lipolysis in adipose tissue. Thus, it is a promoter of catabolic metabolism.