Why do atheromas form before thrombi when the endothelium tears?

[Cheman]

Atheroma and thrombi...

I have read that atheromas usually result when a tear occurs in the endothelium occurs which allows phagocytes and LDL's to enter, etc.
Why does this occur rather than a thrombus form first? Afterall, clots form when we cut ourselves as a result of the blood being exposed to collegen - surely this would be exposed when a tear occurs in the endothelium?

Also, I have read that atheromas, as they are rigid, can break and this leads to formation of thrombi - is this because collegen in vessal walls is exposed, or something inside the atheroma?

Thanks in advance.

 

[Monique]

I have read that atheromas usually result when a tear occurs in the endothelium occurs which allows phagocytes and LDL's to enter, etc.

Actually the LDL accumulates underneath the endothelium without there being a tear. Also, macrophages can enter the endothelium by squeezing themselves so there is no tear.

So, what happens is that LDL accumulates, macrophages are attracted that try to eat the LDL, the macrophages overeat and die, more macrophages get attracted due to an inflammation response, endothelial cells start to replicate, this thickening of endothelium leads to a narrowing of the bloodvessel. The narrowing of the bloodvessel can be dangerous when it leads to an obstruction, but it is more dangerous to have an unstable plaque which can tear. You are correct that this leads to thrombi formation, because a chemical that is called TF (tissue factor) is released from the inner part of the vessel wall that activates coagulation.