The Circulatory System is the process of blood and other substances being pumped around the body by the heart and blood vessels.

The Heart has the function of the heart is to pump blood around the body and to every cell in the body.

The location of the heart is between the two lungs of our body and is similar in shape to a grape fruit. As the heart contracts, the blood is pushed through valves. These valves only let the blood flow one way, like a one-way system.
The heart has to squeeze very hard to make the blood go through (the pressure is enough to make a hole in the ceiling above where you are now). It makes it harder if your blood vessels are blocked with cholesterol. That is why it is important not to smoke and live a healthy lifestyle.

The Blood is composed of three substances. These are platelets, blood cells and plasma.

Platelets are responsible for clotting the blood; there are dead cell fragments. A deficiency of platelets causes the disease Haemophilia.

Plasma is a yellow liquid which is composed of 90% water, the rest carries carbon dioxide diffused from body cells to go to the lungs, hormones, medication, salt, urea and digested food.

Blood cells come in two different types: Red blood cells and white blood cells.

Red Blood cells carry oxygen around the body, there have no nucleus so there is more space for oxygen and they don't require it. The oxygen is carried by a pigment, haemoglobin which, when reacted with oxygen forms oxyhaemogobin. These cells have a life span of three months.

White Blood cells are the fighters of the body against foreign bodies.
These come in two forms: phagocytes which engulf then dissolve their prey and lymphocytes, which patrol the body searching for foreign bodies lymphocytes have an antibody which will attach to a certain antigen of a bacteria and hold it (antibody and antigen are both protein compounds).

Blood Vessels come in three types, arteries, veins and capillaries.

Arteries carry oxygenated blood away from the heart in exception to the pulmonary artery which carries deoxygenated blood away from the heart to the lung. The arteries walls have to be strong and thick to withstand the intense pressure of the blood when it comes out from the heart.

Veins carry deoxygenated blood to the heart in exception to the pulmonary vein which carries oxygenated blood to the heart from the lungs. Because the blood pressure is lower, the walls of the veins are not as thick. They have larger lumens to help blood flow. They also have valves to keep the blood travelling in the right direction.

Capillaries carry food and oxygen direct to the body tissue and remove waste produts. Their walls are incredibe thin to allow diffusion to take place. They are to small to see from the naked eye.