Medicine & USMLE


Endocrine & Hormones
  1. Leptin
  2. Ghrelin
  3. Protein Hormones
  4. Steroid Hormones
  5. Insulin
  6. Diabetes
  7. Glucagon
  8. Epinephrine
  9. Cortisol
  10. Thyroid Hormones
  11. Calcitonin
  12. Parathyroid Hormone (PTH)
  13. Anterior Pituitary
  14. Prolactin
  15. Luteinizing Hormone (LH)
  16. Follicle-Stimulating Hormone (FSH)
  17. Growth Hormone (GH)
  18. Posterior Pituitary


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