venous blood vessels and atherosclerosis - (Apr/07/2006 )

Hi,
I have a doubt,tried to clear thru articles,but cant.kindly tell me why venous blood vessels are not affected by atherosclerosis,but when it is grafted as artery in bypass,it can have atherosclerosis,why such a process dont occur there,any molecular reasons?
Thank you in advance for any answers

Atherosclerosis is due to macrophages laying cholesterol down (making foam cells) under the internal wall of the vessel. Arterial walls are much thicker than veins becuase they are under much higher pressure. When veins are grafted in to replace arteries their walls become hypertrophied. The macrophages can then "hide" fat under the internal "carpet." If the vein wall is at all weak there is a big risk of rupture. Equally, the foam cells weaken the vessels as well. I'm not at all sure how long it takes for the venous wall to thicken.

One other factor, I wonder if there is a concentration gradient between arteries and veins of triglycerides, cholesterol and lipoproteins. If so, and if the veins have the lower concentration, perhaps that helps to explain the absence of artherosclerosis in these vessels.

Thank you verymuch for your prompt reply