This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Which is not synthesized by the vascular epithelium? \nSelect and explain. \nA. Prostacyclin, B. Angiotensin 2, C. Endothelin, D. Heparin', 'role': 'user'}, {'content': "Answer: B \nExplanation: Endothelial cells constitute a large and impoant tissue. They secrete many growth factors and vasoactive substances. The vasoactive substances include prostaglandins and thromboxanes, nitric oxide, and endothelins.Lungs activate angiotensin I to angiotensin II; this reaction is paicularly prominent in the lungsRef: Ganong's Review of Medical Physiology;23rd edition; Page No: 606", 'role': 'assistant'}]