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


Prolactin is a protein hormone that is produced by the anterior pituitary gland. Prolactin functions at the breast tissue to promote the production of milk, or lactation. Prolactin production is normally regulated by PIF, or Prolactin Inhibitory Factor, which is constantly released by the hypothalamus in order to inhibit prolactin release. When PIF is no longer released, say in the context of childbirth, prolactin levels increase to promote lactation in preparation for breastfeeding.

Key Points

  • Prolactin
    • Type: Peptide 
    • Origin: Anterior Pituitary 
    • Trigger: Stopped release of PIF from hypothalamus
      • PIF = Prolactin Inhibitory Factor
      • PIF inhibits the release of Prolactin. PIF is constantly released by hypothalamus, so when it is no longer released, Prolactin is released.
    • Target: Breast tissue
      • Effect: Promotes lactation
        • Lactation = milk production