Which hormone is primarily responsible for regulating blood glucose levels?

Insulin is the hormone primarily responsible for regulating blood glucose levels. It is produced by the pancreas and plays a critical role in maintaining glucose homeostasis in the body. When blood glucose levels rise after eating, insulin is released to facilitate the uptake of glucose by cells, allowing them to use it for energy or store it as glycogen in the liver and muscle tissues. This action lowers blood glucose levels and is essential for preventing hyperglycemia.

In contrast, glucagon works to raise blood glucose levels when they are low by stimulating the liver to release stored glucose. Cortisol is a steroid hormone involved in various functions, including stress response and metabolism, but it generally has the effect of increasing blood glucose levels during times of stress. Adrenaline, another hormone, primarily prepares the body for 'fight or flight' responses and can also increase blood sugar levels but is not the primary regulator. Thus, insulin's unique role in promoting the uptake of glucose makes it the key hormone for blood glucose regulation.