Medicine & USMLE

Vitamin A (Retinol) Biochemistry

  1. Vitamin B1 (Thiamine) Biochemistry
  2. Vitamin B1 (Thiamine) Deficiency
  3. Vitamin B2 (Riboflavin)
  4. Vitamin B3 (Niacin) Biochemistry
  5. Vitamin B3 (Niacin) Deficiency and Excess
  6. Hartnup Disease
  7. Vitamin B5 (Pantothenic Acid)
  8. Vitamin B6 (Pyridoxine)
  9. Vitamin B7 (Biotin)
  10. Vitamin B9 (Folate)
  11. Vitamin B12 (Cobalamin) Biochemistry
  12. Vitamins B9 and B12 Deficiencies
  13. Vitamin A (Retinol) Biochemistry
  14. Vitamin A (Retinol) Deficiency and Excess
  15. Vitamin C (Ascorbic Acid) Biochemistry
  16. Vitamin C (Ascorbic Acid) Deficiency and Excess
  17. Vitamin D Biochemistry
  18. Vitamin D Deficiency and Excess
  19. Vitamin E (Tocopherol/Tocotrienol)
  20. Vitamin K Biochemistry
  21. Vitamin K Deficiency
  22. Zinc
  23. Kwashiorkor and Marasmus


Vitamin A is a group of fat-soluble compounds that includes retinol, retinal, retinoic acid, and several provitamin A carotenoids (notably beta-carotene) found in leafy greens. Vitamin A is an antioxidant, and it has a number of functions.  These functions include growth and development, cell differentiation and immune maintenance, the formation of visual pigments, and the treatment of acne (isotretinoin) and measles. ATRA (all-trans retinoic acid), a form of vitamin A, is used to treat the APL, also known as acute promyelocytic leukemia (subtype of AML).

Key Points

  • Retinol (Vitamin A)
    • Antioxidant found in:
      • Wild game/animal products, especially liver (preformed vitamin A)
      • Leafy vegetables (as beta-carotene precursor)
    • Fat-soluble
      • Fat malabsorption in biliary/pancreatic insufficiency (e.g. cystic fibrosis) can cause Vitamin A Deficiency
    • Constituent of retinal visual pigments
      • Deficiency or excess can affect vision
    • Maintains normal cell differentiation
      • epithelial cells into specialized tissue (pancreatic cells, mucus-secreting cells)
        • prevents squamous metaplasia
      • Promyelocytes into mature granulocytes
        • Mechanism of action for treating APL (subtype of AML)
    • Inhibits sebum production in sebaceous glands
      • used to treat cystic acne
    • Also used to treat measles

Find Vitamin A Biochemistry and other Vitamins among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.