What is the role of thyroxine (T4) in the body?

Thyroxine (T4) plays a crucial role in the body primarily by helping to maintain normal body metabolism. It is produced by the thyroid gland and is instrumental in regulating various metabolic processes, including the rate at which the body uses energy and synthesizes proteins. When T4 levels are balanced, they support overall metabolic efficiency, influencing how the body converts food into energy. An adequate supply of T4 is essential for proper growth, development, and function of various systems in the body, including the cardiovascular and digestive systems.

While T4 can indirectly influence heart rate and blood pressure by way of its metabolic effects, its primary and most critical role is in metabolism. Therefore, option B accurately reflects the primary function of thyroxine in the body.