Parathyroid hormone (PTH) is responsible for regulating the levels of calcium and phosphate throughout the body. It is released from the four parathyroid glands, located around the thyroid gland in the neck.

When calcium levels are too low, PTH is released. It acts on the bones, kidneys and the intestine to restore normal calcium levels in the blood. The diagram below shows how PTH acts on the various areas of the body.

  • Kidneys – The kidneys are key in regulating mineral levels. PTH acts on the kidneys directly to increase the amount of calcium that is reabsorbed into the blood, and to increase the amount of phosphate that is excreted in the urine.
  • Bone – PTH stimulates the release of calcium and phosphate from the bones of the skeleton into the blood.
  • Gut – PTH triggers the conversion of vitamin D into the active form in the kidney. Active vitamin D acts in the gut to increase the amount of calcium and phosphate that is absorbed by the intestine.