The organ primarily responsible for regulating metabolism is the thyroid gland. Located in the neck, the thyroid produces hormones, predominantly thyroxine (T4) and triiodothyronine (T3), which play a key role in controlling the body's metabolic rate. These hormones influence how the body uses energy, affecting processes such as heart rate, digestion, and temperature regulation. Proper thyroid function is essential for overall health, as imbalances can lead to disorders like hypothyroidism, characterized by a sluggish metabolism, or hyperthyroidism, involved in an overly active metabolism.