It flows through all of our veins, and although it
looks identical from person to person, there is a lot more than meets the eye
with blood. Firstly, a common misconception is that blood is just a red liquid
that flows through our veins and arteries when in actual fact it is much more
complex. Blood is a series of cells suspended in plasma:
- Erythrocytes – the biconcaved red blood cells are the most abundant and are the principal means of delivering oxygen to body tissues via the circulatory system.
- Leukocytes – these white blood cells are the immune effectors. There are several types of white blood cells with a range of specific and general immune functions.
- Platelets – important for coagulation. At a site of interruption, platelets prevent bleeding by clotting (thus the formation of scabs).
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| The constituents of blood. |
Most of us have heard the term “blood type” especially
if you are generous enough to donate your blood, but many people do not
understand the key differences between the blood types and why certain people
cannot receive specific blood types based on the composition of their
erythrocytes (red blood cells). Also did you know that there are currently 33
recognised human blood group systems? However it is commonly divided into 4
main groups: A, B, AB and O (known as the ABO system), and these 4 groups can
either be RhD positive or RhD negative.
The ABO system is determined by the presence of
specific glycoproteins on the surface of the red blood cells known as antigens.
Antigens are unique, microscopic markers that need to be matched correctly
otherwise complications can arise during blood transfusions. Differentiation is
relatively simple, if the red blood cells are covered in A antigens then that
person is blood type A. If they are covered in B antigens then they are type B.
Both A and B antigens type AB and if they have neither then they will be categorised
as O. The significance of matching blood groups in transfusion is a result of
antibodies associated with blood types. For instance, blood type A has
antibodies against B antigens (and vice versa) meaning they are recognised as
foreign to the body disposed of immunologically. Type O blood has antibodies
against A and B antigens whilst AB blood has no antibodies at all. This seems
fairly complicated with lots of letters being thrown around so I will do my
best to simplify it.
- Blood Type O – has no antigens so can be universally donated as no antibodies can recognise it as foreign. Unfortunately as it has antibodies against A and B, people with type O blood can receive blood from the O group only. (Universal donor)
- Blood Type AB – Has no antibodies so can receive blood from any other blood group. (Universal recipient)
- Blood Type A – Can receive blood from type A and O but will reject type B and AB due to antibodies against B antigens.
- Blood Type B – Can receive blood from type B and O but not A or AB due to antibodies against A.
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| Simple representation of the surface antigenic make up of red blood cells. |
To make matters slightly more complicated blood
types also fall under the Rh system. This is based on 5 Rhesus antigens: C, c,
D, E and e. Most important is the D antigen whereby the presence of which makes
a blood type positive and absence negative. The presence of the D antigen can
also cause a transfusion reaction so the true universal donor blood type is O-
as it has no A, B or Rh antigens for a recipient to reject.
So there you have it, a brief overview of what is going on in your
veins. It is all well and good to understand what your blood type is but it is
much more important to do something with it. The volume of blood in an adult
human is approximately 5 litres. When donating blood a mere 470mls are taken
and that is regenerated pretty rapidly (fluid in less than 24 hours, red blood
cells in 3 weeks and iron in around 8 weeks). For those of you that haven’t donated
blood before I urge you to do so. The nurses are always accommodating to those
who are nervous with needles and it is far from painful. About half as sore as
a wasp sting when the needle enters then no pain during the process. Some
people experience slight dizziness and or light-headedness but the free tea,
coffee and biscuits quickly squares you up. Donating blood is such a simple act
that benefits so many people in cases of transfusions, serious accidents, cancers,
childbirth, bone marrow failure and surgeries to name a few.
In closing I urge you to do something incredible.
Give blood. Look for your local donation times and dates here:
https://www.scotblood.co.uk/
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