Blood groups

The blood groups were discovered around 1900, when it was observed that blood collected for transfusions was compatible in some recipients but not in others. It has been found that each person spontaneously forms antibodies against antigens that his/her own red blood cells lack.

The surface of erythrocytes has molecules called antigens, and in the plasma there are molecules called antibodies. An antibody is very specific, meaning it can combine only with certain antigen. When the antibodies in the plasma bind to the antigens on the surface of the erythrocytes, they form molecular bridges that connect the erythrocytes together. As a result, agglutination of the cells occurs. The combination of the antibodies with the antigens can also initiate reactions that cause hemolysis or rupture of the erythrocytes. Because the antigen-antibody combination can cause agglutination, the antigens are often called agglutinogens, and antibodies are called agglutinins.

All humans and many other primates can be typed for the ABO blood group. Everyone in the world can be classified into four categories: A, B, AB and O. Definition of each category depends on the 'antigens' present on red blood cells, and the 'antibodies' present in the blood plasma. In the ABO blood group type A blood has type A antigens, type B blood has type B antigens, type AB blood has both types of antigens. Type O blood has neither A nor B antigens. In addition, type A blood has plasma with type B antibodies. Type B blood has plasma with type A antibodies. Type AB blood has no plasma antibodies. Type O blood has both A and B plasma antibodies.

Another important blood group is the Rh blood group, so named because it was first studied in the rhesus monkey. People are Rh positive if they have a certain Rh antigen (the D antigen) on the surface of their erythrocytes, and they are Rh negative if they do not have this Rh antigen.

The ABO blood type and the Rh blood type usually designated together. For example, a person designated as A positive is type A in the ABO blood group and Rh positive.

In parts of Europe the "O" in ABO blood type is substituted with "0" (zero), signifying the lack of A or B antigen. In Ukraine and some other countries blood types are referenced using numbers and Roman numerals instead of letters. This is Janský's original classification of blood types. It designates the blood types of humans as I, II, III, and IV, which are elsewhere designated, respectively, as O, A, B, and AB.

Ex. 12. Translate the following words and word-combinations into English:

Утворювати антитіла; поверхня еритроцитів; переливання крові; донор; реципієнт; резус-позитивний; містити антитіла; виявляти; поверхня.

Ex. 13. Answer the following questions:

1. When were the blood groups discovered? 2. How many main blood types are distinguished? 3. What is ABO blood grouping based on? 4. What does the typing of Rh-factor depend on? 5. What blood is said to be Rh-positive?

Ex. 14. Write out key words of the text “Blood Groups”.

Ex. 15. Make up a plan of the text “Blood Groups”.

Ex. 16. Give a summary of the text “Blood Groups”.

Дата добавления: 2015-07-11