The Functions of the Thyroid
One of the body's largest endocrine glands, the thyroid, controls the rate at which the body burns energy through the production of thyroid hormones, including thyroxine (T4) and triiodothyronine (T3). It also adjusts the body's sensitivity to other hormones. The thyroid gland is located between the laryngeal prominence (Adam's apple) and the collarbone. It has a right and left lobe, with a bridge (aka isthmus) in between, which looks like a butterfly.
The Functions of the Parathyroid Gland
The four parathyroid glands are small endocrine glands behind the thyroid that produce parathyroid hormone (parathormone or PTH.) These glands maintain calcium levels within a narrow margin for proper function of the nervous and muscular systems. They accomplish this through calcium-sensing receptors which, when activated, release PTH into the blood. When the level of calcium in the blood falls too low, the parathyroid glands secrete just enough PTH to restore the blood calcium level.