Video Transcript
The ABO system is used to define
the blood groups in humans. What two substances in the blood
does it use to do this? (A) The genetic material found in
red blood cells and the proteins found in platelets. (B) Antigens found on the surface
of red blood cells and antibodies found in the blood plasma. (C) Antigens found on the surface
of white blood cells and platelets found in the blood plasma. Or (D) antibodies found in the
blood plasma and lymphocytes found on the surface of red blood cells.
The question is asking us about the
ABO system. So let’s first take a moment to
review what this system is. An antigen is a substance that
triggers an immune system response, especially the production of antibodies. Antigens are present on the surface
of many cells, including red blood cells. Two of the possible antigens
displayed by red blood cells are called A and B antigens. The ABO system refers to the
presence or absence of these A and B antigens on red blood cells.
The two types of antigens give rise
to four blood groups. Type A blood has A antigens on the
surface of its red blood cells but does not have B antigens. Type B blood has B antigens but
does not have A antigens. Type AB blood has both A and B
antigens, and type O blood has neither A nor B antigens on its red blood cells.
Antibodies are proteins that bind
to or recognize specific antigens on the surface of cells, marking those cells for
destruction by other immune system processes. Antibodies are found on the surface
of B cells, as well as circulating in the blood plasma. Circulating antibodies can be
directed against antigens that are not expressed on our own red blood cells. For example, anti-A antibodies bind
to A antigens, marking any red blood cells that display A antigens for destruction,
while anti-B antibodies bind to B antigens, marking any red blood cells that display
B antigens for destruction.
So members of blood group A have
anti-B antibodies but do not have anti-A antibodies. Otherwise, their immune systems
would attack their own blood cells. Members of blood group B have
anti-A antibodies but do not have anti-B antibodies. Members of blood group AB have
neither anti-A nor anti-B antibodies. And members of blood group O have
both anti-A and anti-B antibodies.
When antibodies recognize their
specific antigens on the surface of red blood cells, they bind to them, causing the
blood cells to clump together in a process known as agglutination. For example, if blood cells from a
type B donor are mistakenly introduced into the body of a type A receiver, their
anti-B antibodies agglutinate the red blood cells from the type B donor.
Now that we’ve reviewed the ABO
system, what is it that defines the blood groups? Well, the specific antigens on the
surface of red blood cells are certainly one defining feature of a person’s blood
group. Additionally, the antibodies
produced by an individual against foreign blood antigens play an important role in
determining blood group, because they limit the types of blood an individual can
safely receive and donate.
Therefore, the correct answer
choice is (B). The two substances in the blood
that define the blood groups are antigens found on the surface of red blood cells
and antibodies found in the blood plasma.
