5.5 What is blood?

So, having learned about how blood moves around the body, let's now look at what it's made up of and therefore why we need it at all, and why its health has an effect on sporting performance.

Blood has four main components – three types of cell and the watery liquid that holds these cells. Briefly, these four components are:

• Red blood cells these cells give blood its characteristic colour. They make up about seven per cent of blood and their main function is to carry oxygen molecules. The oxygen molecules attach to the red blood cells, and are carried around the body in the blood.
• White blood cells these are cells that make up about one per cent of blood. The main role of white blood cells is to fight infection. When there is a problem somewhere in the body, white blood cells in that area attack microbes such as bacteria or viruses and other impurities to try and stop the infection.
• Platelet cells these are cells whose main role is to create blood clots to help stop bleeding. When part of the blood flow system is broken (such as in a wound, both internal and external), these platelet cells move into the opening and block it, helping to stop more blood flowing out of the system.
• Blood plasma this is the watery liquid that carries the blood cells.

The blood is the body's main way of moving important material around. We've seen that oxygen is taken in through the lungs and gets to where it is needed by travelling in the blood, and this is carried along by red blood cells. The blood also carries nutrients around the body, once again by red blood cells.

The next section will combine what you've learned about the heart and blood by looking at the cardiovascular system, what we mean by an efficient cardiovascular system and how this affects athletes in a variety of sports.