What are blood vessels?
Blood flows around your body inside a network of tubes called blood vessels. There are three types of blood vessel: arteries, veins and capillaries. The blood in arteries comes straight from the heart and is pumped under pressure, so the artery walls are thick and muscular. Blood moves from arteries to veins through tiny capillaries, which are about one-tenth the thickness of a human hair. Capillaries are so narrow that red blood cells have to squash themselves up to pass through. Veins return blood to the heart, and because the pressure is now lower, they have thinner walls than arteries.
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Why can too much cholesterol be bad for you?
Cholesterol is a natural fatty substance that is found in many foods such as dairy produce, eggs and meat. It is also produced naturally in the body. High levels of cholesterol in the blood can sometimes collect on the inside of arteries, like the fur inside a kettle. This gradually reduces the blood flow and can lead to the formation of a clot that may break off and block smaller arteries. Sometimes an artery becomes almost completely blocked by these cholesterol deposits. It becomes so narrow and rigid that it cannot expand to let enough blood pass through. This kind of blockage usually happens in the legs, and is a common result of cigarette smoking.
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