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: Pathology
Ultra-structurally, endothelial cells contain: 
Select and explain. 
A. Weibel Palade bodies, B. Langerhan’s granules, C. Abundant glycogen, D. Kallikrein
A: Weibel Palade bodies
Answer: A: Weibel Palade bodies 
Explanation: Endothelial cells are the major source of plasma vWF, whereas most factor VIII is synthesized in the liver. vWF is found in the plasma (in association with factor VIII), in platelet granules, in endothelial cells within cytoplasmic vesicles called Weibel-Palade bodies, and in the subendothelium, where it binds to collagen.
Reference-Robbins BASIC PATHOLOGY 10th edition pg-490