What are the characteristics of a healthy endothelium?

A healthy endothelium may be characterized by its ability to do the following: 

• Regulate the vasodilation and vasoconstriction of blood vessels: Healthy endothelial cells help the blood vessels constrict or dilate depending on internal and external stimuli as well as changes in temperature.
• Control the amount of fluid traveling from the blood to the tissues: A healthy endothelium has just the right amount of permeability so that fluids can travel in between its cells to reach the tissues while still being tight enough to form a barrier preventing toxins and foreign substances from entering the bloodstream. 
• Prevent thrombosis: Blood clots that form during thrombosis obstruct the free flow of blood, resulting in serious consequences. A healthy endothelium produces substances such as nitric oxide and prostacyclin that help maintain blood fluidity and prevent unwanted clotting.