Glucagon plays a critical role in blood sugar regulation by increasing glucose levels in the bloodstream. Produced by the alpha cells of the pancreas, glucagon stimulates the liver to convert stored glycogen into glucose through a process called glycogenolysis. This hormone is essential during periods of fasting or low carbohydrate intake to maintain homeostasis in blood sugar levels. It acts in opposition to insulin, which lowers blood sugar, thus balancing the body's energy requirements and ensuring that cells receive adequate fuel to perform essential functions.