What is the primary function of glucagon in the body?

Glucagon plays a crucial role in maintaining blood sugar levels by promoting the release of glucose into the bloodstream. It is a hormone produced by the alpha cells of the pancreas and acts primarily when blood sugar levels fall too low, a condition known as hypoglycemia. The main physiological actions of glucagon include stimulating glycogenolysis, which is the breakdown of glycogen stored in the liver into glucose, and promoting gluconeogenesis, the synthesis of glucose from non-carbohydrate sources. By increasing the availability of glucose in the bloodstream, glucagon ensures that the body's cells have a sufficient supply of energy, especially critical for the functioning of vital organs such as the brain.

Other options, while relevant to metabolic processes, do not capture the primary function of glucagon. For instance, stimulating digestive enzymes pertains more to the actions of hormones like gastrin and secretin, promoting fat storage is primarily regulated by insulin, and stimulating red blood cell production is controlled by erythropoietin, primarily produced by the kidneys. Thus, the key role of glucagon is clearly centered on the regulation of blood sugar levels, making it the correct choice in this context.