What is the primary action of glucagon in the body?

Glucagon's primary action in the body is to increase blood sugar levels. It is a hormone produced by the alpha cells of the pancreas and plays a crucial role in glucose metabolism. When blood glucose levels are low, glucagon is released into the bloodstream.

Glucagon triggers the liver to convert stored glycogen into glucose, a process known as glycogenolysis. This newly released glucose then enters the bloodstream, elevating blood sugar levels to help maintain homeostasis. In addition, glucagon can promote gluconeogenesis, the synthesis of glucose from non-carbohydrate sources, further contributing to increased blood glucose levels when needed.

In contrast, lowering blood sugar levels is primarily the action of insulin, another hormone produced by the pancreas. Similarly, stimulating protein synthesis and suppressing appetite involve different hormonal mechanisms and pathways, such as those involving insulin and other hormones like leptin and ghrelin. Hence, the unequivocal role of glucagon in raising blood sugar levels supports why it is the correct answer.