If you watched the second episode of the recent “Watermen: A Dirty Business” series on BBC Two, you will have seen how drains are often blocked because hundreds of litres of cooking fat is poured down household sinks every week. Over time the fat builds up inside the pipework, particularly at joints and bends, eventually blocking the pipes and causing the rather unpleasant consequence of sewage spewing out onto the roads! The process of fat blocking our sewage pipes is reminiscent of what happens in our own arteries.
Hardening can occur for several reasons; calcium deposits can build up in the tunica media. Or a process called intimal hyperplasia can occur (please don’t worry too much about the jargon!) where smooth muscle cells multiply excessively and move towards the inner layer of the artery wall. ‘Intimal’ refers to the innermost layer of the artery – the intima, and ‘hyperplasia’ refers to the excess reproduction or multiplication of cells. Additionally the smooth muscle cells produce proteins such as collagen and elastic fibres further hardening and clogging up the artery.
But the main type of arteriosclerosis causing major problems in the human population, and primarily responsible for heart attacks and strokes, is atherosclerosis. It is a disease that takes decades to develop and inflict its potent consequences on us but by the time we know it’s happening, it is often too late. So what exactly is atherosclerosis? As you read the next part, watch this video which may help you visualise the disease (video created by 3FX medical animation inc.):
The artery tries to tackle this problem by expanding outwards to increase the diameter of the artery, and by moving smooth muscle cells from the wall to the surface of what is now a developing atherosclerotic plaque. The smooth muscle cells create a ‘cap’ at the surface separating blood flow from the plaque as exposure of dead cells to flowing blood can trigger the formation of a blood clot. Eventually the artery cannot expand any further and so the growing plaque begins to constrict blood flow. The growing plaque can be enough to obstruct blood flow. Narrowing of the artery also causes the flowing blood to exert force on the cap and weaken it eventually causing it to burst open or rupture. A blood clot will then form on the surface, which may or may not block blood flow in the artery. If blood flow is blocked in the coronary arteries supplying blood to heart muscle, a heart attack occurs and some of the heart muscle can die. Alternatively blocking blood flow to part of the brain, either by a blood clot or part of a plaque dislodging and blocking the small blood vessels in the brain, leads to a stroke.
So atherosclerosis is an extremely complex process with many different factors involved, hence why it is so difficult to treat. Research is vital to fully understand this disease and improve existing treatments. Much like cancer, which is so difficult to treat because cancer in each patient can be caused by a different mutation in a different gene, thus we cannot use a ‘one size fits all’ drug.
Now that you know what atherosclerosis is, I will explore how you can reduce your risk of suffering from a heart attack or stroke in my next post.