Atherosclerosis

Atherosclerosis is the progressive build-up of fatty deposits - often called 'plaques' - inside the arteries.[1]

The first step in this process is when damage occurs to the inner lining of the arteries (the epitheliumThe outer layer of cells covering the open surfaces of the body, both over external surfaces and lining hollow structures.). A number of factors can cause this damage: high bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. pressure, increased levels of fatty substances called lipoproteins in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid., or chemical toxins - from cigarette smoke, for example.[2]

The damage to the epitheliumThe outer layer of cells covering the open surfaces of the body, both over external surfaces and lining hollow structures. means that it no longer acts as a protective barrier, so that several substances can pass through it from the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid.. These substances make up the plaqueAny flat, raised patch; for example, a raised patch on the skin, fatty deposit in the inner wall of an artery, or layer over the surface of a tooth.. For example, lipoproteins and white bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cells pass through the abnormal epitheliumThe outer layer of cells covering the open surfaces of the body, both over external surfaces and lining hollow structures. and infiltrate the wall of the arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood..

One type of white bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cellThe basic unit of all living organisms., called a T-cellA kind of lymphocyte, a type of white blood cell that fights infection., brings about inflammationThe body’s response to injury., and also stimulates increased numbers of smooth muscleA type of muscle responsible for actions in the body that we are not aware of; for example, the muscles that constrict blood vessels. cells. Smooth muscleTissue made up of cells that can contract to bring about movement. cells produce a tough fibrous substance at the site.[1] All of these factors contribute to the developing plaqueAny flat, raised patch; for example, a raised patch on the skin, fatty deposit in the inner wall of an artery, or layer over the surface of a tooth..[2]

Ongoing inflammationThe body’s response to injury., with more infiltration of lipoproteins and white bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cells, means that the plaqueAny flat, raised patch; for example, a raised patch on the skin, fatty deposit in the inner wall of an artery, or layer over the surface of a tooth. continues to grow over time.[2]

Unfortunately, some of these plaques are prone to rupturing or wearing away. This exposes the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. flowing through the arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood. to the inner contents of the plaqueAny flat, raised patch; for example, a raised patch on the skin, fatty deposit in the inner wall of an artery, or layer over the surface of a tooth., which act like a framework for the formation of a bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. clot, or thrombusA blood clot..

This clot may cause a partial or complete blockage within the arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood., or some of the clot may break off and be carried away in the bloodstream (an embolusA clot (or other material, for example, fat or air) that has become dislodged from a point in the blood system and travels in the circulation before lodging elswhere.), where it may cause a blockage within another arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood..[2] Either way, if the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. flow to the brain is restricted, the direct outcome may be a stroke.

References: 
  1. Boon NA, Colledge NR and Walker BR. 'Davidson's Principles and Practice of Medicine'. Churchill Livingstone Elsevier. 2006; 20th edition.
  2. Toth PP. Subclinical atherosclerosisDisease leading to fatty deposits in the inner walls of the arteries, which reduce and may eventually obstruct blood flow.: what it is, what it means and what we can do about it. Int J Clin Pract. 2008; 62(8):1246-54.