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5 Facts about Blood

Find out all the important things your blood does for you
1. What’s in your blood?

More than half of your blood is plasma, a pale liquid that carries your blood cells and chemicals around your body.  These include red blood cells, white blood cells and platelets.

  • Red blood cells carry oxygen around the body, they also collect carbon dioxide and take it back to the lungs for you to breathe it out.
  • White blood cells defend your body against things like bacteria, viruses and infections.
  • Platelets are ‘sticky cells’ that help your blood clot, stopping the bleeding when you cut yourself.

2. How is it transported?

Blood travels around the body through blood vessels. These carry blood to the heart and away from the heart.

Arteries carry the blood containing oxygen from the heart to the rest of the body. Blood then travels through the veins back to the heart and lungs to collect more oxygen.

You can feel your heart beating at points around your body where large arteries run close to the skin, like on your neck and wrists. This is called a pulse.

3. What is blood pressure?

Blood pressure is the measurement of the force with which your heart pumps blood around your body. The blood pressure measurement is made up of two numbers:

  • The pressure when the heart pumps
  • The pressure when the heart rests between beats

People talk about blood pressure as the first number ‘over’ the second number. Normal ranges for young people are 100-130 over 60-85; for example 120/65.

4. What jobs does blood do?

  • Blood transports oxygen and energy-giving nutrients around the body
  • In the liver and kidneys, your blood is filtered and cleaned of waste products. Your blood also takes carbon dioxide to the lungs to be breathed out.
  • Blood regulates body heat, taking the heat produced by the organs to the outer parts of our body. This means we stay warm, but our organs don’t overheat.


5. What types of blood are there?

Red blood cells have markers on their surface, called antigens. These identify the blood cells that belong to us.

There are only four blood types, these are:





It was later discovered that there is another antigen, named the rhesus factor (after the Rhesus Monkeys that were being studied when the discovery was made). This means people from the same blood group will have either ‘rhesus positive’ or ‘rhesus negative’ markers, so in fact rather than four blood types, there are actually eight.

When someone isn’t making enough red blood cells, or they have lost a lot of blood and can’t make more of it quickly enough, for example following a major trauma, they will need a blood transfusion. The blood that is given to them will need to be matched exactly so the body doesn’t fight it and destroy it.

You can choose to donate your own blood to help in these kind of situations. Find out more about becoming a blood donor here.

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