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Blood Type
(Microsoft Encarta)

Blood Type
There are several types of red blood
cells and each person has red blood cells of just one type. Blood
type is determined by the occurrence or absence of substances, known as
recognition markers or antigens, on the surface of the red blood cell. Type A
blood has just marker A on its red blood cells while type B has only marker B.
If neither A nor B markers are present, the blood is type O. If both the A and B
markers are present, the blood is type AB. Another marker, the Rh antigen (also
known as the Rh factor), is present or absent regardless of the presence of A
and B markers. If the Rh marker is present, the blood is said to be Rh positive,
and if it is absent, the blood is Rh negative. The most common blood type is A
positive?that is, blood that has an A marker and also an Rh marker. More than 20
additional red blood cell types have been discovered.

Blood typing is important for many
medical reasons. If a person loses a lot of blood, that person may need a
blood transfusion to replace some of the lost red blood cells.
Since everyone makes antibodies against substances that are foreign, or not of
their own body, transfused blood must be matched so as not to contain these
substances. For example, a person who is blood type A positive will not make
antibodies against the A or Rh markers, but will make antibodies against the B
marker, which is not on that person?s own red blood cells. If blood containing
the B marker (from types B positive, B negative, AB positive, or AB negative) is
transfused into this person, then the transfused red blood cells will be rapidly
destroyed by the patient?s anti-B antibodies. In this case, the transfusion will
do the patient no good and may even result in serious harm. For a successful
blood transfusion into an A positive blood type individual, blood that is type O
negative, O positive, A negative, or A positive is needed because these blood
types will not be attacked by the patient?s anti-B antibodies.

Resumos Relacionados

- White Blood Cells

- Giving Blood

- Hiv-1 Antibody Test (elisa And Western Blot). (senior Health Advisor 2005)

- Hiv-1 Antibody Test (elisa And Western Blot). (senior Health Advisor 2005)

- Plasma

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