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Your blood

Your blood is an amazing thing – it is a transport system, a heating system and a defence system!  Blood transports oxygen and nutrients to all the areas of your body that need them and they pick up any waste products, like carbon dioxide, and brings it to the waste disposal areas of your body, like your lungs and kidneys.  Your blood makes sure that every part of your body is warm by transporting the heat that is made in the middle of your body to the outer bits like your fingers or toes.  Just remember though that if you go out in the cold without your socks, your feet will still get cold!  Very importantly, your blood carries your second line of defence, your immune system that fights invaders and keeps you healthy.

Your blood travels around your body in your blood vessels.  These are miles and miles of arteries and veins that are joined together by capillaries like a great big complicated motorway!  As your blood travels through your blood vessel motorway, it eventually gets to every cell in your body where it swaps oxygen for waste products like carbon dioxide and delivers nutrients.  Your blood picks up oxygen in your lungs from the air you breathe in and removes carbon dioxide from your body when you breathe out.  When your blood is carrying oxygen (oxygenated blood), it is a bright red colour, like you see if you get a cut that bleeds.  When the oxygen is taken by your blood cells (de-oxygenated blood), it is a dark purple or even blue colour!  Still, if you have a cut and this deoxygenated blood is exposed to the air, it will turn the bright red colour you normally see! 

Once your veins carry the de-oxygenated blood through your lungs, your blood becomes a bright red colour again because it swaps waste products for oxygen.  This bright red oxygenated blood continues its journey to your heart and gets pumped back around to all the different cells in your body, transporting oxygen where it is needed.  Your circulatory system is a great big circle that keeps your cells working!


So what is blood made of?  Over half of your blood is plasma, a pale, clear, yellow liquid in which all the blood cells are suspended.  You have millions of red blood cells in every drop of your blood.  Red blood cells have haemoglobin that contains iron and carries the oxygen you breathe around to every cell in your body.  Your red blood cells also carry carbon dioxide waste to your lungs which you get rid of by breathing out.

White blood cells in your blood are the second line of defence in your body – they are cells of your immune system.  White blood cells (like Luke O’Cyte) find and fight any invaders that manage to get through your first line of defence and work very hard to keep you healthy.  You don’t have as many white blood cells as you do red blood cells in each drop of blood, but your body does make more if you are sick or if your have an infection.  Your white blood cell defences are supported by antibodies.  These are proteins in your blood that travel around fighting infections.  Each antibody is unique, it only recognises it’s the one disease it can fight, but they are really important in keeping you healthy.  Antibodies mean you are immune and your body makes them if you have been vaccinated or if you have been sick with a disease.  They stop you getting sick again if the same invaders get past your first line of defence again!

Your skin is very tough but if you get a cut, your blood needs to act fast to make sure that you heal as quickly as possible!  The parts of your blood that do this are your platelets.  These are tiny cells that are very, very sticky.  When you get a cut, your platelets rush to the area and join together to form a clot.  As the clot dries out, it forms a scab that stays until the skin underneath is totally healed.  When your skin is totally healed, and ready to face the world again, the scab falls off - all by itself!

Blood can come in different types and everyone has their own blood type that stays the same throughout your life.  There are just four main types of blood and each of them has a different set of markers to tell your body what they are.  In this way, if your body sees blood with a different type of marker, your immune, your second line of defence, can tell is not yours and destroy it. 


The four different type of blood are:

  • Type A – this has markers of type A only on the surface of the red blood cells
  • Type B – this has markers of type B only on the surface of the red blood cells
  • Type AB -  – this has markers of both type A and type B on the surface of the red blood cells
  • Type O -  – this does not have any markers of type A or type B on the surface of the red blood cells

There is another marker on red blood cells called rhesus that some people have (positive) and some people do not (negative).  Therefore your blood has two identifying markers, type A, type B, type AB or type O and Rhesus type positive or negative.

The markings that tell your body your blood type are very important if you ever need extra blood for instance after surgery or an accident.  This is called a blood transfusion.  There are limits though, you can only get blood that has markers that matches yours otherwise your immune system will destroy it.  So, what type of blood matches?  It really depends on whether you are giving or receiving blood:

  • Type A – this can be given to anyone with type A or type AB blood
  • Type B - this can be given to anyone with type B or type AB blood
  • Type AB – this can only be given to someone with type AB blood
  • Type O – this is called the Universal donor and can be given to anyone, not matter what blood type they have


  • Type A – people with type A can only take blood from someone who is type A or type O
  •  Type B – people with type B can only take blood from someone who is type B or type O
  • Type AB – people with type AB blood can take blood from anyone.  They are the Universal receivers!
  • Type O – people with type O can only take blood from someone who is type O

You may never need to have a blood transfusion at any stage during your life.  It is a good idea, when you are old enough (at 18 years of age), to make sure there is enough blood in stock for people who do need it!  Check out your local blood donation clinics for more information


Did you know…?

  • If you stretched out your blood vessels, your arteries, capillaries and veins, they would stretch for about 60,000 miles when you are a child and almost 100,000 miles when you are an adult!  Your capillaries alone stretch between 25,000 and 60,000 miles!

Check out the Irish Blood Transfusion Supply Board (BTSB) at:  http://www.ibts.ie

Here are some interesting facts from the BTSB website!

  • Human blood travels 60,000 miles per day on its journey through the arteries, arterioles and capillaries and back through the venules and veins.
  • The most common blood group is O, accounting for about 46% of the world's population.  However, in some areas other blood groups predominate, in Norway for example, type A is the most prevalent.
  • 7% of a person's body weight is made up of blood.
  • The minimum age for donating blood is 18.
  • The maximum age for donating blood is 65 (or 60 if you are a first time donor)
  • You can donate every 90 days.
  • The most common blood group in Ireland is O positive (47% of the population)
  • The rarest blood group in Ireland is AB negative (1% of the population)
  • One in four people will need a blood transfusion at some point in their lives
  • Only 5% of the population are regular blood donors
  • People who have lived in the United Kingdom for an accumulative period of 1 year between 1 January 1980 and 31 December 1996 are not eligible to give blood.
  • A unit of blood lasts for just 35 days.
  • An average adult has between  10 and 12 pints of blood
  • Blood carries oxygen and nutrients to all parts of the body
  • Blood carries carbon dioxide and other waste products back to the lungs, kidneys and liver for disposal
  • There are about 1 billion red cells in two to three drops of blood
  • Over 1,000 Irish people receive transfusions every week in Ireland
  • One car accident victim may require up to 30 units of blood, a bleeding ulcer could require anything between 3-30 units of blood and a coronary artery bypass may use between 1-5 units of blood.
  • Approximately 70,000 patients will have transfusions in Irish hospitals this year
  • 3,000 blood donors are needed each week in Ireland
  • The IBTS supplies 71 hospitals in Ireland with blood and blood products 365 days a year
  • People in the West of Ireland are predominantly of blood group O
  • There is a higher concentration of Group A blood in counties which historically received Viking, Anglo Norman and English population settlements
There are more people with Rhesus negative blood on the East coast than the West


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