The 4 parathyroid glands (the size of a grain of rice, shown in yellow in the drawings) are located behind the thyroid; often clinging to it like a shell to its rock; they very precisely control the level of calcium in the blood through the production of parathyroid hormone (PTH) in the event of a lack of calcium - hypocalcemia - the symptoms are numerous and can be serious - tetany).

Preserving the parathyroid glands with their blood vessels is an essential goal during thyroid surgery.