# Vitamin A (Retinol) Biochemistry

**Summary**  
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](/content/view/4026/index.html)  
  - 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](/content/browse#playlist-2700/index.html) among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.