This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
[{'content': "Ultra structurally , endothelial cells contain \nSelect and explain. \nA. Weibel palade bodies, B. Langerhan's granules, C. Abundant glycogen, D. Kallikrein", 'role': 'user'}, {'content': 'Answer: A \nExplanation: ref Robbins 9/e p76 Weibel-Palade bodies (WPBs) are the storage granules of endothelial cells, the cells that form the inner lining of the blood vessels and hea. They store and release two principal molecules, von Willebrand factor and P-selectin, and thus play a dual role in hemostasis and inflammation.', 'role': 'assistant'}]