Atherosclerosis literally means porridge-like hardness and is derived from the Greek word "athere" meaning gruel. Atherosclerosis is the medical term for hardening of the arteries which is the common expression used to describe the problems associated with the peripheral vascular disease. 

Most people use the term hardening of the arteries usually when they are speaking about an elderly friend or relative. However, atherosclerosis must not be confused with the normal ageing process where some of the changes seen in the arterial wall are similar. It is remarkable that early changes in the arteries can be seen in children as young as three years of age. These changes normally take the form of a fatty streaks and are believed to occur when minor trauma to the blood vessel leads to a temporary localised a loss of the endothelial cells thus exposing the underlying media. 

Microscopic cells in the blood called platelets rapidly stick to the area and these in turn secretes substances which cause the smooth muscle cells in the media to migrate upwards. These smooth muscle cells transform into cells which look similar to the endothelial cells to form a new lining. It is believed that during the process the trapped platelets and a substance called proteoglycan attract low density lipoproteins from the blood. 

It may also be that the fatty substances also get there by leaking through the temporary gap in the vessel lining. A third explanation is that the smooth muscle cells that have had to form the repair have altered fat metabolism and they are responsible for the fatty streaks. Whether the fatty streaks lead on to more harmful lesions is not known but everybody develops them sooner or later so it seems unlikely, that on their own, they are responsible for the more harmful effects of arterial disease. 

As we get older the intimal lining of our arteries gets thicker. The internal elastic membrane becomes fragmented possibly due to irritation caused by the presence of fat. It reduplicates in response but sadly the same cannot be said of the media which gradually gets thinner with age. This can lead to a weakness and widening of the arteries over time and the vessels also become longer leading to tortuosity. Widened arteries can reach a considerable size and these swellings are called aneurysms.

The repetition of the repair process mentioned above leads to the development of fibrous plaques. Evidence of these lesions can be found in people as young as 20 but do not appear to increase in number in normal people until at least the 4th decade following which they increase progressively. Fibrous plaques can become complicated in one of several ways:

• They can reduce the human of of the artery sufficiently to cause significant diminution of flow leading ultimately to thrombosis of the blood vessel.

• They can ulcerate and discharge small particles of their lipid core into the distal circulation. This can lead to serious consequences if the distal circulation happens to be a vital organ such as the brain.

• Haemorrhage can occur into them leading to stripping of the lining of the blood vessel called a dissection. This can lead to sudden blockage of the artery with devastating results.

• Collagen, the protein which makes up the fibrous substance within the plaque has an affinity for calcium. Calcium is therefore deposited into the tissues surrounding the plaque particularly the elastic proteins with in the media. It is this that causes the hardening of the artery and in any medium sized or smaller thick walled artery this can cause severe reduction in the flow through the vessel due to the loss of elastic recoil of the vessel wall.