Which hormone plays a key role in regulating metabolism and energy expenditure?

Thyroxine (T4) is a crucial hormone produced by the thyroid gland that regulates metabolism and energy expenditure in the body. It influences the metabolic rate, which is the rate at which the body converts food into energy. T4 increases the rate of cellular respiration and oxygen consumption, facilitating the breakdown of carbohydrates, fats, and proteins for energy. This process is essential for maintaining body temperature, supporting growth and development, and ensuring overall energy balance.

While insulin, cortisol, and adrenaline also play significant roles in metabolism, they do not primarily regulate the basal metabolic rate in the same way that T4 does. Insulin primarily regulates blood glucose levels, cortisol manages stress responses and influences metabolism under certain conditions, and adrenaline prepares the body for 'fight or flight' responses, increasing heart rate and energy availability in acute situations. In contrast, T4 directly influences the metabolic processes that sustain energy levels in a more continuous and integrative manner. Thus, the primary role of regulating metabolism and energy expenditure is attributed to thyroxine.