Video Transcript
In this video, we will learn how to
classify blood groups and why this classification is important. In addition, we will learn how to
apply this knowledge of blood groups and Rhesus factors to practice medicine
safely.
The blood that travels in the human
body is incredibly important. It’s made of two main components, a
fluid called plasma and blood cells. It delivers nutrients to cells as
needed and oxygen needed for the cell survival and helps to remove waste products
from cells including carbon dioxide. If someone has an accident and
loses a lot of blood, these functions might not operate effectively. In this case, it might be necessary
to transfuse some blood that was donated from another person in order for the cells
to still receive everything they need for survival. However, not every person can give
blood to a person in need. If a patient receives blood from
the wrong person, this can lead to serious complications and even death. So why is this? It’s because different people can
have different blood groups. And if the donor and recipient
aren’t matched properly, this can cause serious problems.
The classification of a person’s
blood group depends on two different substances found in their blood, antigens and
antibodies. Antigens are substances that can
cause an immune response in the body. This means that some antigens are
recognized as foreign and the body can attack them. One of the ways the body fights
antigens is by making special proteins called antibodies. Antibodies are produced by the
immune system to attach to one specific type of antigen. This helps the immune system
identify and destroy foreign cells or structures.
Now let’s look at the different
blood groups and see what kind of antigens and antibodies we see. There are four different blood
groups in humans, A, B, AB, and O. They’re named this way because of
the antigen they have on the surface of the red blood cell. Blood group A has a type A antigen
on its surface. Each antigen is coded by different
alleles or versions of the same gene. For the type A antigen, it’s
encoded by the IA allele. So for someone with blood group A,
they have two copies of the IA allele that make the type A antigen. There’s another possibility here
also that they have the IA allele and the IO allele. But we’ll discuss that in a
moment.
People with blood group B have the
type B antigen on the surface of the red blood cells. This antigen is coated by the IB
allele. So people with blood group B will
either have two copies of the IB allele or one copy of the IB allele and one copy of
the IO allele. People with blood group AB have the
type A antigen and the type B antigen on the surface of the red blood cells. They have both. This happens when the person has
the genotype IA IB. This is interesting because often
when a person has two different alleles of a gene, one often dominates over the
other and only the phenotype caused by this allele is shown. In this particular case, neither
allele IA nor IB is dominant over the other one. So both alleles are expressed. This is called codominance.
Finally, in blood group O, neither
type A nor type B antigens are present. This is caused by the IO allele,
which is recessive and doesn’t produce a functional antigen. These individuals have two copies
of the IO allele. Since IO doesn’t produce any
functional antigen, when it’s combined with IA, only the IA allele produces a type A
antigen. So this is why the combination of
IA and IO can give blood group A. And the same applies for blood
group B.
As mentioned, the classification of
a person’s blood group depends on two substances found in their blood, antigens and
antibodies. The antibodies present in the blood
can be divided into two types, anti-A and anti-B. Antibodies are produced when
something foreign is introduced into the body. Anti- means against. So for someone with blood group A,
they will produce type A antigens on the surface of their red blood cells. These type A antigens aren’t
foreign. So anti-A antibodies wouldn’t be
produced. Instead, type B antigens would be
foreign. So anti-B antibodies would be
produced.
The same can be said for someone
with blood group B. They’ll contain type B
antigens. So they won’t produce anti-B
antibodies but will instead produce anti-A antibodies because the type A antigen
would be foreign. So this answers the question we had
at the beginning of the video, which asked why not every patient can receive blood
from any donor. If someone with blood group A were
to donate to someone with blood group B, this person’s immune system would recognize
the blood as foreign and produce anti-A antibodies to fight against it. These anti-A antibodies would
destroy all the donor’s red blood cells, and the blood transfusion would be
rejected.
So what about blood group AB? Because the red blood cells of
blood group AB present both type A and type B antigens, neither anti-A nor anti-B
antibodies will be produced. And in blood group O, which doesn’t
produce either A or B antigens, both anti-A and anti-B antibodies will be
produced.
Now let’s look and see what blood
groups are compatible for blood transfusions. Everyone is able to receive blood
from their own blood group. However, some people can also
receive blood from other blood groups. Because blood group AB doesn’t
produce antibodies against type A or type B antigens, it can receive blood from any
of the other blood groups. People with blood group AB are
therefore sometimes called universal receivers. Because blood group O doesn’t have
any antigens on its red blood cells, any blood group can receive blood from blood
group O because the immune system will not produce antibodies against it. People with blood group O are
therefore sometimes called universal donors.
Now that we know what blood groups
are and how they’re defined, how can we find out what blood group a patient has? We can do this through a phenomenon
called agglutination. As mentioned, anti-A antibodies
will bind to the type A antigen found in someone with blood group A. Notice that this antibody has
another site to bind antigen. And of course, multiple antibodies
can bind to antigen on multiple red blood cells. By forming these complexes between
the red blood cells and the antibodies, the blood will begin to clump or
agglutinate.
So to determine what blood group a
person has, we can simply take some blood and mix it with anti-A antibodies and
anti-B antibodies. So if we take a drop of blood from
blood group A and then mix in some anti-A antibody, the type A antigens on the red
blood cells of blood group A will bind to the anti-A antibody. This will cause the blood to form
clumps.
So then, what happens if we take a
drop of blood group A and then mix it with anti-B antibodies? Well, nothing really because the
anti-B antibody can’t recognize the type A antigen, so it doesn’t bind. The anti-B antibody will only
recognize a type B antigen. So in this example, the drop of
blood will not clump. But when we take a drop of blood
group B and mix it with anti-B antibody, the anti-B antibody can bind to the type B
antigen on this blood group, which we can see here. This causes the blood to clump. And if we mix blood group B with
the anti-A antibody, the anti-A antibody won’t recognize the type B antigen. So it will not clump.
So what about blood groups AB and
O? Why don’t you pause the video for a
moment and see if you can work it out? Blood group AB has both type A
antigen and type B antigen. So adding either anti-A antibodies
or anti-B antibodies will cause the blood to clump. And in blood group O, there is no
antigen present on the surface of the red blood cells. So adding either anti-A or anti-B
antibodies will not cause the blood to clump. So by mixing drops of blood with
anti-A and anti-B antibodies, we can determine which blood group the drop belongs
to.
By using our knowledge of blood
groups and the alleles that determine them, we can use this information to figure
out how blood groups are inherited. Here, we can draw out a Punnett
square to see how these different alleles are inherited. The child always inherits one copy
of an allele from each parent. The blue alleles are from the
biological father, while the pink alleles are from the biological mother. The phenotype of the child or the
corresponding blood group based on the inherited alleles is shown in orange. The IA and IB alleles are
dominant. And they display codominance when
inherited together to give the AB blood group. The IO allele is recessive, and you
need two copies of it to get blood group O.
Understanding this can help
determine the paternity of a child in family disputes. So if the mother has blood group O,
the father has blood group AB, and the child has blood group O, then the possible
combinations of alleles from these parents can only give blood groups A and B. So in this case, the child with
blood group O is very unlikely to be the biological child to this father. These alleles can give rise to
different antigens, either type A or type B on the surface of red blood cells.
There’s another antigen we need to
discuss called Rhesus factor. For the Rhesus factor antigens,
there are only two choices. Either a person has these antigens
on the surface of their red blood cells and is Rh positive or does not have these
antigens and is Rh negative. Understanding Rhesus factors is
incredibly important. A person with Rh negative blood
should only receive blood transfusions that are also Rh negative. Otherwise, antibodies will form
against the Rhesus antigen and this will lead to rejection of the blood
transfusion.
Rhesus factor is also important to
consider during pregnancy. So if a male who’s Rh positive and
a female who’s Rh negative conceive an Rh positive child, the mother’s blood may
start to mix with that of the unborn child by the placenta. Her immune system will then produce
antibodies against the baby’s Rh positive blood. If this is a first-time pregnancy,
then this is likely to be okay. However, if she becomes pregnant a
second time with an Rh positive baby, then these antibodies might target the fetus
and lead to complications. This can be prevented by treating
the mother with a special serum that prevents her immune system from developing
antibodies against the Rh antigens in the baby’s blood.
Now let’s take a moment to apply
what we’ve learned with a practice question.
Blood can be transfused between
individuals. The diagram provided shows which
blood group can receive blood from or donate blood to other groups. A student says, “People with blood
group A can receive blood from any other blood group.” Are they correct? Why? (A) No, as people with blood group
A cannot receive blood from those with blood group AB or group B. (B) No, as people with blood group
A cannot receive blood from those with group O or group AB. Or (C) yes, as the diagram
demonstrates that all other blood groups can donate blood to group A.
In order to answer this question,
let’s look at how these different blood groups are classified. Before we can do this, let’s first
clear the answer choices so we have more room to work with. There are four different blood
groups: A, B, AB, and O. Someone with blood group A has red
blood cells with type A antigen present on their surface. Someone with blood group B has red
blood cells with type B antigens present on their surface. You may have already guessed it,
but someone with blood group AB has red blood cells with type A and type B antigens
present on their surface. And finally, someone with blood
group O has red blood cells with neither type A nor type B antigens present on their
surface.
For each blood group, there are
also different antibodies that are present. In blood group A, there are anti-B
antibodies. These anti-B antibodies have a
specific shape that allows them to bind specifically to type B antigen. When this happens, an immune
response is initiated and the red blood cell is destroyed. So people with blood group A can’t
receive blood from blood group B because these anti-B antibodies would destroy those
red blood cells. And the same is true for blood
group AB because they also contain type B antigens. However, anti-B antibody can’t bind
to the person’s own type A antigen because the antigen isn’t compatible with this
antibody.
In someone with blood group B, they
have anti-A antibodies, which would react with any red blood cells that carry the
type A antigen. So someone with blood group B would
not be able to accept donations from those in blood group A or blood group AB
because they carry the type A antigen. A person with blood group AB
contains neither anti-A nor anti-B antibodies. If they did, then these antibodies
would attack their own red blood cells. Because they don’t have any anti-A
or anti-B antibodies, this person can receive blood from any blood group. Finally, a person with blood group
O has both anti-A and anti-B antibodies, so they would only be able to receive blood
from blood group O. And since they don’t have any
antibodies, they can donate to any of the blood groups.
All of this is indicated in the
provided diagram. O is able to donate blood to any
blood group, while AB is able to receive blood from any blood group. And groups A and B can only receive
blood from O or from their own blood group. So if we look at the statement in
this question that people with blood group A can receive blood from any other blood
group, this is incorrect because blood group A can’t receive blood from groups AB or
B.
Now let’s take a moment to go over
the key points in this video. The human blood groups are A, B,
AB, and O. Blood groups are classified based
on antigens on the surface of red blood cells and antibodies. We can use agglutination to
determine blood groups. Not all blood groups are
compatible, and this can cause serious harm if it isn’t considered. The antigens for blood groups are
encoded by different alleles, which have a predictable pattern of inheritance. Rhesus factor is another antigen
that needs to be considered during pregnancy and blood transfusions.
