Thyroid is a small butterfly-shaped gland inside the neck, located in front of the trachea (windpipe) and below the larynx (voicebox). Thyroid glandproduces two thyroid hormones - triiodothyronine (T3) and thyroxine (T4) that travel through the blood to all tissues of the body.
Thyroid hormones regulate basic metabolism of body (that is how the body breaks down food and either uses that energy immediately or stores it for the future). The functioning of thyroid gland is controlled by pituitary gland (located at the base of the brain), which produces thyroid-stimulating hormone (TSH). The bloodstream carries TSH to the thyroid gland, and signals the thyroid gland to produce more thyroid hormones, as needed.