What is the primary function of glucagon in metabolism?

The primary function of glucagon in metabolism is to raise blood glucose levels. Glucagon is a hormone produced by the alpha cells of the pancreas and acts primarily when blood glucose levels are low, such as during fasting or between meals. It stimulates glycogenolysis, the process of breaking down glycogen stored in the liver, into glucose. This glucose is then released into the bloodstream, effectively increasing blood sugar levels to provide energy for various bodily functions.

Additionally, glucagon also promotes gluconeogenesis, the metabolic pathway through which glucose is synthesized from non-carbohydrate precursors, further contributing to the elevation of blood glucose. This hormone plays a critical role in maintaining glucose homeostasis, ensuring that the body has a continuous supply of glucose, especially for the brain and other vital organs that rely heavily on glucose as an energy source.

In contrast, the other options relate to different metabolic pathways. For instance, promoting lipid synthesis is primarily a function of insulin, which encourages the storage of fat. Lowering blood glucose levels is another role of insulin, not glucagon. Similarly, enhancing protein synthesis is also a predominant effect of insulin rather than glucagon. Therefore, glucagon's role as a key regulator of blood glucose levels highlights its importance in energy