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


Epinephrine is a hormone that is produced by the adrenal medulla. Epinephrine is a tyrosine-derivative that is hydrophilic, and can therefore easily dissolve in water and blood to move throughout the body. Once epinephrine reaches a target cell, it relies on external receptors outside of the cell to trigger a second messenger cascade inside the cell, in order to cause epinephrine’s downstream effects. Epinephrine is produced when we are stressed, and stimulates the fight-or-flight response. During this response, epinephrine increases blood flow to skeletal muscles and reduces blood flow to digestive organs or other organs not necessary for survival.

Key Points

  • Epinephrine
    • Norepinephrine has the same endocrine function as Epinephrine
    • Origin: Adrenal Medulla
    • Type: Tyrosine derivative
      • Water-soluble (hydrophilic)
        • Cannot diffuse across cell membrane
        • Uses GPCR pathway
          • Uses a secondary messenger system because Epinephrine acts like a hydrophilic protein hormone
    • Trigger: Stress
    • Effects:
      • Increases blood flow to skeletal muscles
      • Constricts blood vessels/reduces blood flow to most organs
      • Promotes glycogenolysis in liver
      • All actions by epinephrine are designed to promote the fight or flight response