FIGURE. The endothelium as an organ is more than a collection of endothelial cells.

Like the orderly arrayed carpet of cumulus clouds in calm the cells of the quiescent endothelium appear in an ordered arrangement, and in this configuration support expression of critical factors that keep thrombosis, vasomotor tone, inflammation, proliferation and metabolism in check. Endothelial cells in the face of vascular injury resemble chaotic cumulonimbus clouds that appear as dispersed towering harbingers of thunderstorms. The stresses and damage to endothelium with vascular injury (e.g. stenting) not only disrupts the monolayer barrier but leaves behind ill-appearing remnant endothelial cells and recruits progenitor cells of a clearly different phenotype, both capable of expressing factors that promote what might be viewed as adverse cellular events in a drive to restore homeostasis.