Medicine & USMLE

Thyroid Hormones

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


Thyroid hormones, which include T3 and T4, are hormones produced by the thyroid gland. The production pathway of these hormones happens in several steps. First, thyroid-releasing hormone, or TRH, is released from the hypothalamus. TRH then stimulates the anterior pituitary to release thyroid-stimulating hormone or TSH, the second step in the pathway. Finally, TSH acts on the thyroid gland to promote release of the thyroid hormones T3 and T4.

Key Points

  • Thyroid Hormones
    • T3 = Triiodothyronine
    • T4 = Thyroxine
    • Origin: Thyroid
    • Pathway:
      • TRH from hypothalamus
      • TSH from anterior pituitary
      • Thyroid Hormones
    • Type: Tyrosine derivatives
      • Steroid-like
    • Trigger: TSH stimulation from anterior pituitary
    • Target: Whole body
      • Effect: Increases metabolic rate
        • Metabolic rate is often measured as the amount of energy of energy expended in one day