What the thyroid does

The thyroid works closely with two other hormone-producing glands, the pituitary and the hypothalamus. These three act in concert to balance the thyroid's hormone output, enabling the body to produce just the right amount of energy just when it needs it - low during sleep, higher when we are awake, higher still when we are active.

The pituitary, a pea-sized gland at the base of the brain, controls the thyroid's function with its own thyroid-releasing hormone. The pituitary itself is activated by thyrotropin-releasing hormone from the hypothalamus, a cherry-sized region of the brain just above the pituitary.

It is the T3 and T4 hormones secreted by the thyroid that play a major role in controlling the way our body functions are maintained and our energy is created and used up (our metabolism). They are essential for children's physical growth and mental development. Calcium is also key to growth and healthy bones. Calcium levels are regulated by calcitonin from the thyroid and by parathyroid hormone, which is produced by four pea-sized parathyroid glands located just behind the thyroid.