What effect does glucagon have on blood glucose levels?

Glucagon plays a critical role in regulating blood glucose levels, particularly during periods of fasting or low blood sugar. It is a hormone produced by the alpha cells of the pancreas, and its primary function is to increase blood glucose levels. When blood sugar levels drop, glucagon is released into the bloodstream, signaling the liver to convert stored glycogen into glucose, which is then released into the bloodstream. This mechanism ensures that the body has an adequate supply of glucose to meet its energy needs, especially between meals or during physical activity. Therefore, the correct answer is that glucagon increases blood glucose levels.