Which hormone can raise blood glucose levels when they drop too low?

The hormone that plays a crucial role in raising blood glucose levels when they drop too low is glucagon. Glucagon is produced by the alpha cells of the pancreas and acts primarily in the liver to stimulate the conversion of glycogen to glucose through a process called glycogenolysis. This release of glucose into the bloodstream helps to restore normal blood sugar levels, ensuring that the body has the energy it needs to function properly.

While adrenaline can also influence blood glucose levels, its primary role is to prepare the body for a "fight or flight" response, leading to various metabolic changes, including the release of glucose, but it does not act directly to increase blood glucose in a regulatory fashion. Insulin, on the other hand, decreases blood glucose levels by facilitating the uptake of glucose into the cells. Cortisol plays a role in glucose metabolism and can increase blood sugar levels over the long term, but its primary function is related to stress response and metabolism rather than acute regulation of low blood glucose levels.

Thus, glucagon is specifically designed to counteract low blood glucose levels, making it the correct answer.