B3 2.2 Keeping the blood flowing

Blood is carried around your body in three main types of blood vessels, each adapated for a different function.

The blood vessels

Your arteries carry blood away from your heart to the organs of your body. This blood is usually bright red oxygenated blood. The artries stretch as the blood is forced through them and go back into shape afterwards. You can feel this as a pulse where the arteries run close to the surface (like your wrist). Because the blood in the arteries is under pressure, it is very dangerous if an artery is cut. That's because the blood spurts out rapidly every time the heart beats. 

The veins carry blood towards your heart. It is usually low in oxygen and so is a deep purply-red colour. Veins do not have a pulse. They often have valves to prevent the backflow of blood as it moves back to the heart.

The capillaries form a huge network of tiny vessels linking the arteries and the veins. Capillaries are narrow with very thin walls. This enables substances, such as oxygen and glucose, to diffuse easily out of your blood and into your cells. Simailarily the substances produced by your cells, such as carbon dioxide, pass into the blood through the walls of the capillaries.

Problems with blood flow through the heart

If the supply of oxygen to your heart…