Two important hormones released by the thyroid are thyroxin also called T4 and triiodothyronine also called T3. These hormones help regulate the metabolism of carbohydrates, lipids fats and proteins. Specifically, they increase the rate at which cells release energy from carbs, enhance the rate of protein synthesis and stimulate the breakdown and mobilization of lipids. These hormones are essential for normal growth and development and for maturation of the nervous system.