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