Physiology The blood within the vessels does not clot normally because: A Vitamin K antagonists are present in plasma B Thrombin has a positive feedback on plasminogen C Sodium citrate in plasma chelates calcium ions D Vascular endothelium is smooth and coated with glycocalyx 💡 Explanation The blood within the vessels does not clot normally because: ✓ Correct Answer: D. Vascular endothelium is smooth and coated with glycocalyx