These glands produce parathyroid hormones (PTH). This has an important role in controlling the amount of calcium in blood and bones. Calcium is an important element in our body: it is the only element with its own control system (the parathyroid glands).
There are two pairs of parathyroid glands, just behind the thyroid glands. Each gland is about 6 mm long and 3–4 mm wide. Parathyroid glands get their blood supply from the inferior thyroid arteries.