Hormone: A chemical substance produced in an organ, which, carried to an associated organ by the blood stream, influences its functional activity.

Antibody: It is a protein complex used by immune system to identify and neutralize foreign objects like bacteria and viruses.

Thyroid scan: An image obtained from the thyroid gland after oral administration of radioiodine or Technetium.

Ectopic: Located away from normal position.

Endemic: A disease that is constantly present to a greater or lesser degree in people of a certain class or in people living in a particular location.

T3 (liothyronine sodium), T4 (levothyroxine sodium): Thyroid hormones.