What hormone does the thyroid gland mainly secrete to control metabolism?

The thyroid gland primarily secretes T3 (triiodothyronine) and T4 (thyroxine) to regulate metabolism. These two hormones play a crucial role in controlling the body's metabolic rate, influencing how the body uses energy, how sensitive it is to other hormones, and regulating processes such as heart rate and temperature. T3 is the more active form and has a stronger effect on metabolism compared to T4, which is mostly a precursor that gets converted to T3 in various tissues.

Insulin and glucagon are secreted by the pancreas and are mainly involved in glucose metabolism and regulation of blood sugar levels. Cortisol is a hormone produced by the adrenal glands that helps manage stress and has various other functions, but it does not directly control metabolism in the same way that T3 and T4 do. Therefore, the primary role of the thyroid hormones is distinct and specific to metabolic regulation.