http://www.ck12.org Chapter 1. Human Biology
As this woman donates blood, you can see her blood collecting in a special bag. This bag is coded with her blood
type. That makes it possible for doctors and nurses to match up the blood she is giving to a recipient that has the
same blood type.
Blood Types
Do you know what your blood type is? Maybe you have heard people say that they have Type A or Type O blood.
Blood type is a way to describe the type of antigens, or proteins, on the surface of red blood cells (RBCs). There are
four blood types; A, B, AB, and O.
- Type A blood has type A antigens on the RBCs in the blood.
- Type AB blood has A and B antigens on the RBCs.
- Type B has B antigens on the RBCs.
- Type O does not have either A or B antigens.
The ABO blood group system is important if a person needs a blood transfusion. Ablood transfusionis the process
of putting blood or blood products from one person into the circulatory system of another person. The blood type
of the recipient needs to be carefully matched to the blood type of the donor. That’s because different blood types
have different types of antibodies, or proteins, released by the blood cells. Antibodies attack strange substances in
the body. This is a normal part of your defenses against disease.
For example, imagine a person with Type O blood was given type A blood. First, what type of antibodies do people
with type O blood produce? They produce anti-A and anti-B antibodies. This means, if a person with type O blood
received type A blood, the anti-A antibodies in the person’s blood would attack the A antigens on the RBCs in the
donor blood (Figure1.48). The antibodies would cause the RBCs to clump together, and the clumps could block a
blood vessel. This clumping of blood cells could cause death.
FIGURE 1.48
A person with type O blood has A and B
antibodies in his/her plasma; if the person
was to get type A blood instead of type O,
his/her A antibodies would attach to the
antigens on the RBCs and cause them to
clump together.People with type A blood produce anti-B antibodies, and people with type B blood produce anti-A antibodies. People
with type AB blood do not produce either antibody.
The Rhesus Factor
The second most important blood group system in human blood is theRhesus (Rh) factor. A person either has, or
does not have, the Rh antigen on the surface of their RBCs. If they do have it, then the person is positive. If the
person does not have the antigen, they are considered negative.