The hormone that regulates blood glucose is primarily insulin. Insulin is produced by the beta cells of the pancreas. It lowers blood glucose levels by promoting the uptake of glucose from the blood into cells (like liver, muscle, and fat cells) for energy or storage. It also stimulates the liver to convert glucose into glycogen for storage. Another hormone, glucagon, also plays a role in blood glucose regulation, but it acts in the opposite way to insulin. Glucagon raises blood glucose levels by signaling the liver to break down stored glycogen into glucose and release it into the bloodstream. However, when asked which hormone regulates blood glucose, insulin is the most direct and significant answer due to its primary role in lowering high blood sugar.