What happens in atherosclerosis, exactly?

What is it?

Atherosclerosis is a condition in which plaques build up inside the arteries and cause them to harden. It’s prevalence is hard to measure, but it’s safe to say that it is extremely common. Atherosclerosis is the leading cause of cardiovascular disease, and cardiovascular disease is the leading cause of death in the world.

Atherosclerosis often causes no symptoms for decades. If one of these plaques break, however, it can cause a clot to form, and if this clot then goes on to block an important blood vessel, very serious “symptoms” like heart attacks and strokes can occur.

What causes it?

There are lots of factors that are thought to increase the risk of developing atherosclerosis. Factors that are somewhat under our control and that we hence should try our best to avoid include diabetes, cigarette smoking, high blood pressure, and high cholesterol levels.  Factors we cannot control but should be aware of include old age, being male, and having a family history of cardiovascular disease.

In the media atherosclerosis is often associated with “eating the wrong kinds of fat”. The evidence of how different types of fat affect the development of the disease is unclear, but it is generally agreed that it would be best to avoid trans fats.

What happens during it?

Endothelial cells are situated between the bloodstream and the arterial wall. These cells regulate the exchange of substances between blood and tissues, and their unique surface lets things like white blood cells flow through the vessels without sticking to the walls.

Atherosclerosis begins when this endothelial cell layer becomes damaged. This can be triggered by things like high blood pressure and smoking. The injury causes the endothelial cells to produce substances that make white blood cells attach to the endothelial cells and eventually migrate beneath them. These white cells include the precursors of certain white cells called macrophages: macrophages develop when these precursor cells settle into tissue, and then they start engulfing practically anything including the remnants of dead cells as well as invading pathogens like bacteria.

The endothelial cells start to change their shape and the gaps between them start to get bigger. This lets other things, such as protein shells referred to as LDLs that carry cholesterol and fat, enter the space beneath the endothelial cells.

The macrophages then begin to eat the fat that was transported to them by the LDLs. They become full of fat, and then they kill themselves, and the fat stays in store beneath the endothelial cells. Another cells also release substances that cause muscle cells from the artery wall to come to where the fat-filled macrophages are. Eventually these build-ups grow big enough to start disrupting the blood flow in the artery as the “hole” becomes smaller and smaller.

A fibrin cap covers these plaques. If the plaques grow slowly, the cap is strong and there are rarely any problems. If the plaques grow quickly, however, the cap is thin and prone to rupture. If it ruptures, it can trigger the normal process that causes a blood clot to form (and stops us from bleeding to death if we get a papercut). Little blood cells called platelets start releasing substances that cause certain soluble proteins become insoluble, and also makes them more sticky so that they’ll stick to each other. This sticky protein-cell mesh can then travel in the blood vessels. If you’re lucky it will travel for a while and then fall apart, but if you are very unlucky, it will get stuck in an important artery that is supposed to provide oxygenated blood to the heart or the brain. Cells cannot survive for long without oxygen and we cannot survive for long without a functioning heart or brain, so this can have disastrous consequences.

How can it be treated?

The most effective and first treatment is often the modification of lifestyle. This can mean steps like stopping smoking as well as starting to exercise regularly. Changes in diet such as eating more fruits and vegetables can also be very helpful.

Statins are drugs that are very often used for treating people with high cholesterol. They have few side effects, and they have been shown to reduce the risk of cardiovascular disease and death among those who are at a high risk. Statins work by interfering in the reaction series that would ultimately lead to the formation of cholesterol, and hence less cholesterol is produced. These, as well as some other drugs, can be administered in more pronounced cases of atherosclerosis.




Sources: https://en.wikipedia.org/wiki/Atherosclerosis, http://sphweb.bumc.bu.edu/otlt/MPH-Modules/PH/PH709_Heart/PH709_Heart3.html, https://en.wikipedia.org/wiki/Macrophage, https://en.wikipedia.org/wiki/Low-density_lipoprotein, https://en.wikipedia.org/wiki/Coagulation, http://www.heart.org/HEARTORG/Conditions/Cholesterol/WhyCholesterolMatters/Atherosclerosis_UCM_305564_Article.jsp#.WC7hB-Zuy00, https://www.nhlbi.nih.gov/health/health-topics/topics/atherosclerosis, en.wikipedia.org/wiki/Statin



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