Blood is divided into two parts cells 45% and plasma 55% although mostly water it carries nutrients, such as minerals, proteins, glucose, hormones and oxygen and carbon dioxide around the body. The three main type of cells are erythrocytes (red blood cells) leucocytes (white blood cells) and platelets (thrombocytes) The red blood cells main function is to carry oxygen to the body's cells, these contain haemoglobin (which contains iron) that helps these cells bind to the oxygen molecules to carry it around the body. White blood cells function is mainly defending the body from infection and platelets are tiny little fragile cells that when damaged as in an injury release substances to cause the blood to clot thus stemming the flow of blood.
There are 4 main groups A, B, AB and O and these can be either Rh positive or Rh negative so blood can be one of 8 types
The ABO system
Blood groups are defined by the ABO system.
- Blood group A has A antigens on its red blood cells and anti-B antibodies in its plasma.
- Blood group B has B antigens and anti-A antibodies in its plasma.
- Blood group O has no antigens but both anti-A and anti-B antibodies. This means that group O red cells can safely be given to anyone. It is the most common blood group in the UK.
- Group AB has both A and B antigens but no antibodies, otherwise it would destroy itself.
Receiving blood from the wrong ABO group could be life-threatening because antibodies in a person with group A blood will attack group B antigens and vice-versa.
The Rh system
Red blood cells sometimes have another antigen, a protein known as the RhD antigen. If this is present, your blood group is RhD positive. If it is absent, you are RhD negative. This means that you can be one of eight blood groups:
- A RhD positive (A+)
- A RhD negative (A-)
- B RhD positive (B+)
- B RhD negative (B-)
- O RhD positive (O+)
- O RhD negative (O-)
- AB RhD positive (AB+)
- AB RhD negative (AB-)
Around 85% of the UK population is RhD positive.
96% of us rely on the other 4% to give blood. Please don't leave it to someone else.
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