.
.Blood Types
Learn About Blood Type
by Regina Bailey
Our blood is composed of
blood cells and an aqueous fluid known as plasma.
Human blood
type is determined by the presence or absence of certain
identifiers on the surface of red blood cells.
These identifiers, also
called antigens, help the body's immune system to
recognize it's own red blood cell type.
There
are four main ABO blood type groupings: A,
B, AB, and O. These blood groups are determined by the antigen
on the blood cell surface and the antibodies present in the blood plasma.
Antibodies (also
called immunoglobulins) are specialized proteins that identify and defend
against foreign intruders to the body.
Antibodies recognize and bind
to specific antigens so that the foreign substance can be destroyed.
Antibodies
in an individual's blood plasma will be different from the antigen type present
on the red blood cell surface.
For example, a person with
type A blood will have A antigens on the blood cell membrane and type B
antibodies (anti-B) in the blood plasma.
While the genes for most
human traits exist in two alternative forms or alleles, the genes that
determine human ABO blood types exist as three alleles (A,
B, O).
These multiple alleles are
passed from parent to offspring such that one allele is inherited from each
parent.
There are six possible
genotypes (genetic makeup of inherited alleles) and four phenotypes (expressed
physical trait) for human ABO blood types.
The A and B alleles are
dominant to the O allele.
When both inherited alleles
are O, the genotype is homozygous recessive and the blood type is O.
When one of the inherited
alleles is A and the other is B, the genotype is heterozygous and the
blood type is AB.
AB blood type is an example
of co-dominance since both traits are expressed equally.
· Type A: The genotype is either AA or AO.
The antigens on the blood cell are A and the antibodies in the blood plasma are
B.
· Type B: The genotype is either BB or BO.
The antigens on the blood cell are B and the antibodies in the blood plasma are
A.
· Type AB: The genotype is AB.
The antigens on the blood cell are A and B. There are no A or B antibodies in
the blood plasma.
· Type O: The genotype is OO.
There are no A or B antigens on the blood cell. The antibodies in the blood
plasma are A and B.
Due to the fact that a person
with one blood type produces antibodies against another blood type, it is
important that individuals be given compatible blood types for transfusions.
For example, a person with
blood type B makes antibodies against blood type A.
If this person is given blood
of type A, his or her type A antibodies will bind to the antigens on the type A
blood cells and initiate a cascade of events that will cause the blood to clump
together.
This can be deadly as the
clumped cells can block blood vessels and prevent proper blood flow in the
cardiovascular system.
Since people with type AB
blood have no A or B antibodies in their blood plasma, they can receive blood
from persons with A, B, AB, or O type blood.
In addition to the ABO group
antigens, there is another blood group antigen located on red blood cell surfaces.
Known as the Rhesus
factor or Rh factor, this
antigen may be present or absent from red blood cells.
Studies performed with the
rhesus monkey lead to the discovery of this factor, hence the name Rh factor.
Rh Positive or Rh Negative
If the Rh factor is present on the blood cell surface, the blood
type is said to be Rh positive (Rh+).
If absent, the blood type is Rh negative (Rh-).
A person who is Rh- will
produce antibodies against Rh+ blood cells if exposed to them.
A person can become exposed
to Rh+ blood in instances such as a blood transfusion or a pregnancy where the
Rh- mother has an Rh+ child.
In the case of an Rh- mother
and Rh+ fetus, exposure to the blood of the fetus can cause the mother to build
up antibodies against the child's blood.
This can result in hemolytic
disease in which fetal red blood cells are destroyed by
antibodies from the mother.
To prevent this from
happening, Rh- mothers are given Rhogam injections to stop the development of
antibodies against the blood of the fetus.
Like the ABO antigens, the Rh
factor is also an inherited trait with possible genotypes of Rh+
(Rh+/Rh+ or Rh+/Rh-) and Rh- (Rh-/Rh-).
A person who is Rh+ can
receive blood from someone who is Rh+ or Rh- without any negative
consequences.
However, a person who is Rh-
should only receive blood from someone who is Rh-.
Blood Type Combinations
Combining the ABO and Rh
factor blood groups, there are a total of eight possible
blood types.
These types are A+,
A-, B+, B-, AB+, AB-, O+, and O-.
Individuals who are AB+ are
called universal recipients because they
can receive any blood type.
Persons who are O- are
called universal donors because they can
donate blood to persons with any blood type.
No comments:
Post a Comment