The blood in the vessels normally does not clot 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
Correct answer : D. Vascular endothelium is smooth and coated with glycocalyx
Glycocalyx is a general term referring to extracellular polymeric material (glycoprotein) produced by some bacteria, epithelia and other cells. The highly charged glycocalyx of endothelial cells helps prevent platelet adhesion. It also functions to prevent leukocyte adhesion in normal tissues (prevent unwanted inflammation).