Final answer:
The hormone produced by the Parathyroid Glands to help regulate blood calcium levels is Parathyroid hormone (PTH), which increases blood calcium levels when they are low.
Step-by-step explanation:
The hormone that helps maintain the level of calcium in the blood and is produced by the four Parathyroid Glands is Parathyroid hormone (PTH). When blood calcium levels are low, PTH is secreted and it operates to increase calcium levels through various mechanisms. It (1) enhances calcium reabsorption by the kidneys, (2) stimulates osteoclast activity and inhibits osteoblast activity in bones, and (3) promotes the synthesis and secretion of calcitriol by the kidneys, which in turn enhances calcium absorption by the digestive system. PTH and calcitonin, the hormone produced by the thyroid gland, have opposite effects and together they work to maintain calcium homeostasis in the body.