Definition of Thyroid hormone

1. Hyperthyroidism Slideshow Pictures
2. Take the Thyroid Disorder Quiz
3. Thyroid Symptoms and Solutions Slideshow Pictures

Thyroid hormone: A chemical substance made by the thyroid gland for export into the bloodstream. The thyroid gland needs iodine to make thyroid hormones. The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3).

The thyroid gland is located in front of the neck just in front of the trachea.