Why does the blood group
vary from person to person?
Even though the blood of all the human beings looks
alike, in reality, it is not so. Our blood is mainly composed of red blood
corpuscles, white blood corpuscles, platelets and plasma. It has been observed
from microscopic investigations that molecules of antigens found on the surface
of red blood corpuscles are different in different people. Antigen molecules
are a kind of proteins that stimulate the production of antibodies. It is this
difference in the antigen molecules that gives rise to different groups of
blood.
Blood Compatibility
In the year 1900 Dr Karl Landsteiner discovered two kinds
of antigen- A and B type. He was awarded the Nobel Prize for medicine in 1930
for this discovery. Blood containing A type antigen was classified as A group,
while that containing B type as B group. Subsequently, it was discovered that
the blood of some people contains both A and B type antigens. This type was
classified as AB group. The blood that contained neither A nor B type antigens
was called O group. Thus the blood of all human beings has been divided into
four groups. Studies made till now have revealed the existence of more than 200
groups of human blood.
However, as far as the transfusion of blood of nay
patient is concerned, only the aforesaid four groups of blood are important.
Before transfusing blood to any patient, it is essential to get his blood group
tested. It is very essential to match the blood of the patient with that of the
donor before transfusion. It has been found that the blood of even real
brothers and sisters may not be of the same group. On the other hand, the blood
of two individuals belonging to two different states may be of the same group.
If the wrong blood is transfused to patient, he can die,
because antigens of different classes cannot combine with each other. However,
blood plasma of one individual can be given to another because it is the same
in every body.
Landsteiner and Alexander S. wiener discovered another
important blood antigen in 1940. This additional factor is called the rhesus
antigen or Rh factor.
Rhesus antibodies do not occur in naturally blood groups-
both for
recipients and donors. AB
groups are called the universal recipients whereas O is the universal donor.
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