Which hormone is primarily responsible for regulating blood glucose levels?

The hormone primarily responsible for regulating blood glucose levels is insulin. It is produced by the beta cells of the pancreas and plays a fundamental role in lowering blood glucose concentrations. When blood glucose levels rise after a meal, insulin is secreted to facilitate the uptake of glucose into cells, particularly muscle and fat cells, for energy or storage as glycogen.

Insulin also inhibits gluconeogenesis and glycogenolysis in the liver, processes that generate glucose and release it into the bloodstream. This direct action on various tissues to promote glucose uptake demonstrates insulin's essential function in maintaining homeostasis in blood sugar levels.

Other hormones, like glucagon, cortisol, and adrenaline, have roles in glucose regulation, but they primarily act to increase blood sugar levels when it needs to be raised, such as during fasting or stress. Thus, while they contribute to the overall balance of blood glucose, insulin is the key hormone actively working to lower blood glucose levels after meals.