This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Nitric oxide is a potent vasodilator. Where is it produced from? \nSelect and explain. \nA. Endothelium, B. RBC, C. Platelets, D. Lymphocytes', 'role': 'user'}, {'content': "Answer: A \nExplanation: Nitric oxide, known as the 'endothelium-derived relaxing factor', or 'EDRF'. Endothelial cells contain the constitutive form of nitric oxide synthase, which produces moderate amounts of nitric oxide by metabolizing L-arginine. The endothelium of blood vessels uses nitric oxide to signal the surrounding smooth muscle to relax, thus resulting in vasodilation and increasing blood flow. Functions: Endothelium-derived nitric oxide inhibits contraction and proliferation of the underlying vascular smooth muscle, adhesion of blood cells and platelets, and platelet aggregation. Ref: Hypeension Primer: The Essentials of High Blood Pressure By Joseph L Izzo, Jr, Henry R Black, M.D., Theodore L. Goodfriend, 2003, Page 44; Guyton's physiology, 22nd edition, Page 199", 'role': 'assistant'}]