Blood plasma is a yellow liquid which transports all of your blood cells and other substances around your body

Waste carbon dioxide produced by the cells is carried to the lungs

Urea formed by the liver from breakdown of excess proteins is carried to your kidneys where it's removed from the blood and turned into urine

Small, soluble products from digestion pass into the plasma and are transported to individual cells

They pick up oxygen from the air in your lungs and carry it to the cells where it's needed

Biconcave discs - being biconcave increases the surface area to volume ratio for diffusion

Form part of the immune system: lymphocytes form antibodies against microorganisms, some form antitoxins and phagocytes engulf and digest bacteria and viruses

Formed when the enzyme reaction produces protein fibres that capture lots of red blood cells and platelets to form a clot that stops you bleeding to death

Blood is under high pressure in an artery which makes it dangerous if one is cut - the blood will spurt out very rapidly

Arteries stretch as blood goes through and then goes back afterwards. This is felt as a pulse where the arteries are close to the skin

Valves open as the blood flows through and then close if the blood starts to flow backwards.

Form a huge network of tiny vessels linking arteries and veins

Enables substances, like oxygen and carbon dioxide, to diffuse easily out of your blood and into your cells

One transport system carries blood from your heart to your lungs and back again. This allows oxygen and carbon dioxide to be exchanged with the air in the lungs

The other transport system carries blood from your heart to all the other organs of your body and back again

Vital in warm-blooded animals and it makes our circulatory system very efficient

The heart is supplied with oxygen by the coronary arteries

The two sides of the heart fill and empty at the same time, giving a strong, coordinated heartbeat

This allows the left ventricle to develop the pressure needed to force the blood out of the heart and around the whole body

In Coronary Heart Disease, the coronary arteries that supply the heart with blood become narrow. If the blood flow is reduced, then the amount of oxygen that the heart gets is also reduced. A common cause is build up of fatty materials and it can cause pain, a heart attack or even death

Coronary heart disease is often solved using stents, bypass surgery or statins

A stent is a piece of metal mesh which is placed into your artery to keep them open and allow blood to flow through freely. A balloon is inflated into the stent to keep the artery and stent open; when it is deflated the stent stays open. Many also release drugs to stop the blood from clotting.

Bypass surgery is replacing the narrowed or blocked arteries with bits of veins from other parts of the body. This is carried out on heavily damaged arteries and when stents cannot be used. However, it is extremely expensive and comes with the risks of anaesthetic

Statins are drugs which reduce blood cholesterol levels and slows down the rate at which fatty materials are deposited into your arteries. These are prescribed to people at risk of coronary heart disease.

The heart beats at a healthy rhythm of around 70 bpm and is controlled by the natural pacemaker cells

If these stop working, they can cause serious problems

If the heart beats too slow, the body won't get enough oxygen, but if it beats too fast, the heart can't pump blood properly

Electrical device implanted into the chest that weighs 20-50g

Sends strong, regular electrical signals to the heart that stimulate it to beat properly

Modern pacemakers are often very sensitive to what your body needs and only work when the natural rhythm goes wrong. Many stimulate the heart to beat faster during exercise