The 2 main thyroid hormones are T3 (triiodothyronine) and T4 (thyroxine). The thyroid gland plays a major role in the metabolism, growth, and development of the human body. These hormones also support the process of red blood cell formation. Thyroid hormones control the metabolism of carbohydrates, proteins, and fats. Maintenance of water and electrolyte balance is also influenced by thyroid hormones. The thyroid gland also secretes a hormone called thyrocalcitonin (TCT) which regulates the blood calcium levels.