The Blood groups (10th-Biology-Lesson-12.10)

 

Although the blood of all human beings apparently looks alike yet it differs chemically from person to person. The difference lies in the presence of different proteinaceous substances on the surface of erythrocytes. These substances are called antigens. These are the naturally occurring substances on the membranes of the erythrocytes. Particular antibodies are also found in the blood plasma. On the basis of the antigens and antibodies, the human blood is classified into A, B, AB and O blood groups. This is known as the ABO blood group system.

A person having antigen a on his RBCs would have B-antibody in plasma and so he/she would have blood group A. A person with antigen B on RBCs and A-antibody in plasma would have blood group B; a person with both antigens A & B on RBCs and no antibody in plasma would have blood group AB; and a person with neither A nor B antigens on RBCs and both A- and B-antibodies in plasma would have blood group O. (Table 12.1)

Blood can only be transfused between persons having the same blood groups. If it is transfused between persons having different blood groups, the antibodies present in recipient’s plasma destroy the antigen-containing RBCs of the donor. It is called agglutination. Persons with blood group O are called universal donors as they don’t have antigens A or B (also don’t have antigen Rh). They can donate blood to persons with any blood group. The persons with blood group AB are called universal recipients because they don’t have A- and B-antibodies.

Blood Group	Type of antigens on RBCs	Type of antibodies in plasma	Compatible
			Can receive from	Can donate to
A B AB O	A B A , B None	B A None A ,B	A,O B,O A ,B, AB,O O	A,AB B,AB AB A, B, AB, O

 

Table 12.2 Rh factor System

Rh Blood type	Type of antigens on RBCs	Type of antibodies in plasma	Compatable
			Can receive from	Can donate to
Rh+ Rh-	Rh factor None	None Rh-antibody (on stimulation)	Rh+ , Rh- Rh-	Rh+ Rh- , Rh+

 

In addition to the classical ABO blood group system, there is another set of blood groups, the Rh system. The Rh system consists of Rh-positive (Rh) and Rh-negative (Rh) groups. These groups are identified on the basis of the presence of an antigen called Rh factor. If in a person Rh factor is present, he is Rh-positive and if not, he is Rh-negative. These two blood groups are also incompatible i.e. in blood transfusion an Rh-negative person should not be given Rh-positive. On the basis of the Rh factor, the blood groups A, B, AB and O would be A- or A+ , B- or B+ , O- or O+.

“It is always advisable that before giving blood to a person, the blood group compatibility of the donor and the recipients must be checked. The donor and the recipient must have matching blood groups”.

 

Category: 9th 10th