A Recapitulation
- The coronary arteries carry oxygenated, nutrient-rich blood to that amazing little pump called a heart.
- Most heart attacks occur when a coronary artery becomes blocked. The part of the heart muscle supplied by the blocked artery quickly dies.
- Heart muscle does not regenerate. Once part of your heart muscle dies it’s gone forever.
- Those dreaded LDLs seem to play a role in causing arterial blockage and heart attacks.
What is the role of LDLs? How do LDLs cause arterial blockage? These are the questions I’m going to be tackling in my next three posts. The answers are not as straightforward as you may think. In fact, we do not yet know all the answers.
Arteries are not just pipes.
Arteries are not simple pipes that may become clogged up with fat. The old-fashioned “plumbing analogy” is deficient. As this Encyclopaedia Britannica graphic demonstrates, arterial walls have a complex layered structure.
The central core of the artery, where the blood flows, is called the lumen. Moving outwards from the core we find three layers called tunica intima, tunica media and tunica adventita.
The tunica intima, are just plain intima, is itself divided into three layers.
- The endothelium. This is a layer of smooth cells epithelial cells. They provide an even, low-friction inner surface which facilitates the smooth flow of blood.
- Connective tissue which holds everything together
- An elastic membrane. Arterial walls are not rigid. For the arteries to function properly it is necessary that the walls retain some elasticity. As we shall see later “hardening of the arteries” – ie the lost of elasticity in the arterial walls - can lead to serious problems.
The process of plaque formation
In simple terms here’s what happens.
Under certain circumstances LDL particles can penetrate the endothelium – the innermost layer of the arterial wall – and get lodged inside the intima.
Usually this does not matter. An HDL particle will come along, suck out any cholesterol jammed inside the intima and transport it to the liver for recycling or disposal. If for some reason that doesn’t happen we get an accumulation of cholesterol and triglycerides inside the intima.
The LDL particles and their contents accumulating in the intima undergo chemical changes. Specifically their contents, those cholesterol molecules and triglycerides, are oxidised while their proteins are both oxidised and glycated.
For reasons that are not fully understood cells in the arterial wall interpret these chemical changes as a threat and trigger the body’s immune response. What happens then is complicated but the end result is the emergence of an atherosclerotic plaque. You can think of a plaque as a little boil or pimple protruding into the bloodstream with its roots inside the arterial wall. A fibrous “cap” walls off the contents of the plaque from the bloodstream.
In most cases, so long as the plaque is stable, there are no adverse consequences. Occasionally a plaque may grow so big that it significantly constricts the flow of blood. If this happens in the coronary arteries the result may be angina pectoris.
Sometimes, perhaps due to inflammation, the cap of the plaque disintegrates exposing all the detritus inside the plaque to the bloodstream. When that happens a clot forms. If the clot is small and the artery wide enough it will dissolve before any harm is done. Sometimes, however, the clot will completely block an artery. If that happens in a coronary artery the result is a myocardial infarction.
This video illustrates the process.
The above video was produced by AstraZeneca. AstraZeneca is a pharmacieutical company that manufactures and markets a cholesterol lowering drug called Crestor.
You may be wondering why I chose a pharmacieutical company video to illustrate plaque formation during atherosclerosis. That is the subject of my next post.
In the interests of full disclosure, I occasionally use Symbicort, an asthma control medication marketed by AstraZeneca. That is the sum total of my connection with AstraZeneca.
Tags: artery, astrazeneca, atheroma, atheroslcerosis, attack, cholesterol, coronary, crestor, HDL, heart, LDL
[...] 59 second wellness « The Heart Attack Process (1) [...]
[...] In simple terms free radicals are molecules, ions or even some individual atoms that are hungry for electrons. They steal electrons from wherever they can find them. Free radicals are bad news because they can steal electrons from the vital molecules inside your cell thus disrupting the functioning of those cells. Free radicals have been shown to be involved in a variety of serious afflictions from cancer to premature aging. Free radicals are also involved in heart disease. They react with LDL particles stuck in the arterial wall causing inflammation and the immune response that leads to the formation of atheromous plaque. [...]