What is the primary hormone that regulates blood glucose levels?

Insulin is the primary hormone responsible for regulating blood glucose levels in the body. It is produced by the beta cells of the pancreas and plays a crucial role in facilitating the uptake of glucose by cells, particularly in the liver, muscle, and adipose (fat) tissues. When blood glucose levels rise after eating, insulin is released into the bloodstream, promoting the storage of glucose as glycogen in the liver and muscles, and also assisting in converting glucose into fat. This action effectively lowers blood glucose levels to maintain homeostasis.

The other hormones mentioned have roles in glucose metabolism but do not primarily regulate blood glucose like insulin. Glucagon, for example, promotes the release of glucose into the bloodstream during fasting or when blood sugar levels drop. Cortisol, a stress hormone, can influence glucose metabolism as well, often raising glucose levels during stress. Adrenaline, also known as epinephrine, elevates blood glucose levels during the body's 'fight or flight' response, stimulating glycogen breakdown. While all these hormones are important, insulin is unique in its direct and primary function of lowering blood glucose levels, making it the key regulator.