The same platelet activity mentioned above can also be initiated by physical injury to the endothelium. Instead of a swollen monocyte, a tiny injury in the endothelium attracts platelets that clump together. However, monocytes will still be attracted to and penetrate the endothelium. This is brought about by the same chemical that platelets secrete to attract smooth muscle. Two common causes are smoking and high blood pressure .
Cigarette smoke contains chemicals which can damage the endothelial lining.
And increased pressure on arterial walls from high blood pressure may sometimes disrupt the endothelial layer. Whichever way it starts, the process is slow and develops over decades. This gives atherosclerosis a sneaky nature, enabling it to lurk undetected in the arteries for a long time, gradually growing in size. When the effects of atheroschlerosis are finally evident there are often severe, life threatening problems such as heart attacks , strokes or gangrene.