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发表于 25-6-2008 20:36:28
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Blood Types Everybody has a particular blood type. One gene from your mother andone from your father combine to establish your blood type. Those twogenes form a protein (or antigen) that exists on the surface of all redblood cells, and which is capable of stimulating an immune response.
In1901, an Austrian scientist, Karl Landsteiner, found that reactionsbetween substances present in the antigens, and other substances inplasma (antibodies) sometimes cause the red blood cells to clumptogether, causing adverse reactions in recipients. After furtherexperiments, he found four blood groups based on the presence orabsence of two specific antigens which we now know as A and B.
This discovery paved the way for a system of blood grouping called the ABO system
In1939 and 1940, research involving rhesus monkeys identified anothergrouping factor which was called the Rhesus Factor (Rh factor). People,regardless of their ABO blood group, who were found to have a D antigenpresent were grouped as Rh positive and those without the D antigenwere grouped as Rh negative. The rhesus group is indicated by a '+' (Rhpositive) or '-' (Rh negative) after a person's ABO type e.g. A+ or O-.In a similar way to the ABO grouping, people who are Rh positive willhave no Anti-D antibodies in their plasma, while those who are Rhnegative will have Anti-D antibodies. All these groups are geneticallybased.
Are they compatible?
When atransfusion is given, it is preferable for patients to receive blood ofthe same ABO and Rh(D) group. However, in an emergency, if the requiredblood group is unavailable, a patient may be given another group asshown below.
The prevalence of blood types within the community is roughlysimilar to the demand for different blood types, which is why we alwaysask people of all blood types to give blood regularly.
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