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


Insulin is a protein hormone produced by the beta cells of the pancreas. Insulin is released in response to high blood glucose levels, or hyperglycemia. In order to bring blood glucose back down to normal levels, it works to stimulate glucose uptake by all cells, and promotes glucose storage through glycogenesis and other pathways.

Key Points

  • Insulin
    • Peptide hormone
      • Binds to external cell receptors and initiates secondary messenger cascade
        • Causes membrane-bound glucose transporters to open, resulting in glucose movement into cells
    • Origin: beta cells of the pancreas
      • Produced in response to high blood glucose (hyperglycemia)
      • Produced as proinsulin precursor, which must be cleaved in the endomembrane system to produce active insulin (also producing C-peptide)
    • Function:
      • Decreases blood glucose
        • Increased glucose uptake by all cells
        • Increased glycogen production by liver (glycogenesis)
        • Promotes glycolysis
        • Promotes lipogenesis
      • Inhibits glucagon production in alpha cells of pancreas