A thyroid panel is used to screen for or help diagnose hypo- and hyperthyroidism due to various thyroid disorders. Synthetic thyroid medications are made from levothyroxine sodium while natural thyroid Medications are made from desiccated pig thyroid. The other major difference is what thyroid hormones they contain. Most synthetic thyroid medicines, like Synthroid, contain only T4. Natural medications, like Armour, contain both T4 and T3 (triiodothyronine). The function of the thyroid gland is to take iodine and convert it into the hormones thyroxine, and triiodothyronine. These hormones regulate the rate of oxygen use by cells and regulate the generation of body heat. The purpose of the thymus gland is to produce and process lymphocytes or T cells, essential cells in the immune system. The thyroid gland needs iodine to synthesize thyroxine (T4) and tri-iodothyronine (T3), hormones that regulate metabolism and steer growth and development. T4 contains four iodine atoms combined with 27 other atoms of carbon, hydrogen, oxygen, and nitrogen, but owing to its large size accounts for 65 percent of the molecule’s weight.