Calcitonin is a protein hormone produced by the thyroid gland. Calcitonin functions to decrease blood calcium levels in response to high blood calcium. It accomplishes this by two major mechanisms: by inhibiting osteoclast breakdown of bone, and by promoting calcium excretion in the kidneys. In this way, calcitonin works in opposition to parathyroid hormone to maintain calcium levels within a normal range.

Key Points

  • Calcitonin
    • Origin: Thyroid
      • Made from the C-cells of the Thyroid
    • Type: Protein Hormone
    • Trigger: High blood calcium levels
    • Target: Bone 
      • Decreases osteoclast activity
        • Osteoclasts break down bone to move calcium into the blood, so lower osteoclast activity means lower blood calcium
    • Target: Kidneys
      • Increase calcium excretion
    • Effect: Lowers blood calcium levels