The circulatory system is made up of vessels and muscles that help and control the flow of the blood around the body. This process is called circulation. The main parts of the system are the heart, arteries, capillaries and veins. The circulatory system does a very important job in your body. It carries oxygen and essential nutrients to all cells around the body in arteries and carries the waste products and carbon dioxide in veins. The average human body contains over 60,000 miles of blood vessels. What is an artery? Arteries are the pipes that carry blood, rich with oxygen and nutrients, away from the heart. As the blood travels round the arteries, it branches off to be able to deliver oxygen and nutrients to specific cells. The blood in your arteries is bright red and is under high pressure as the heart pumps it around the body. What is a vein? Veins are the pipes that carry deoxygenated blood and waste products around the body. As cells use the oxygen and nutrients delivered by the arteries they create waste products, such as carbon dioxide. The veins then pick up this waste and deliver it around the body for it to be disposed of and then deliver the deoxygenated blood back to the heart. The blood in your veins is under considerably less pressure than in your arteries as it is moving upward back to your heart. Veins have valves in them to stop the blood flowing backwards. What is plaque? Plaque is a build of fat, calcium, cholesterol and other waste products found in your blood. It is very sticky and sticks to the walls of your arteries. The build up of plaque takes many years and hardens as it ages. It narrows your blood vessels and makes it harder for the oxygenated blood to flow around your body and deliver nutrients to your organs. The slow build-up of plaque is caused by high blood pressure, diabetes, smoking, high blood cholesterol, and other modifiable risk factors What is atherosclerosis? As fatty deposits can build up in any of your arteries, it can cause a wide range of symptoms. Plaque build up in the arteries that supply your arms and legs can lead to Peripheral Arterial Disease (PAD), which causes numbness and pain in your arms and legs. If untreated, this can lead to infection, tissue damage and in some cases amputation; atherosclerosis in your carotid artery, that delivers oxygenated and nutrient rich blood to your brain, can cause stroke. More information about vascular disease. More information and advice about vascular health. Whilst we make every effort to ensure that the information contained on this site is accurate, it is not a substitute for medical advice or treatment, and the Circulation Foundation recommends consultation with your doctor or health care professional. The Circulation Foundation cannot accept liability for any loss or damage resulting from any inaccuracy in this information or third party information such as information on websites to which we link. The information provided is intended to support patients, not provide personal medical advice.