Which hormone is primarily responsible for regulating metabolism?

Thyroxine is primarily responsible for regulating metabolism because it plays a crucial role in controlling the body's metabolic rate. Secreted by the thyroid gland, thyroxine influences how the body uses energy, impacting everything from heart rate to how quickly the body burns calories and synthesizes proteins. Increased levels of thyroxine typically lead to an accelerated metabolism, whereas lower levels can result in a decreased metabolic rate, affecting overall energy levels and weight.

Insulin, while important for regulating blood sugar levels and facilitating the uptake of glucose into cells, does not directly regulate metabolism on a broad scale the way thyroxine does. Cortisol, known as the stress hormone, influences metabolism in the context of stress responses, affecting fat and carbohydrate metabolism, but is not the primary regulator of overall metabolic rate. Adrenaline, or epinephrine, is involved in the fight-or-flight response and can temporarily increase metabolic activity but does not serve as a primary hormone for long-term regulation of metabolism. Thus, thyroxine is the key hormone directly linked to metabolic regulation.