Blood, as we know, is an essential fluid that transports the important nutrients to all the organs, circulates the oxygen to the body and collects carbon dioxide, and also helps the human body fight off diseases. The blood type depends on the genes inherited from parents by a person.
A person’s size determines the exact quantity of blood in her/his body. So, it is obvious that everybody has a different amount of blood and this is true with the composition of blood as well. This variation in composition determines an individual’s blood type. Four components make blood- plasma consisting of proteins and salts, red blood cells that dispense oxygen throughout the body, white blood cells that have an essential role to aid the immune system of a body, and platelets helping in the clotting of blood. White blood cells produce antibodies that fight off diseases.
The best among all the systems to group blood is the ABO-system which classifies blood types into four main groups- A, B, O, and AB though each one can be divided into positive and negative. The blood group of a person is determined by the type of antigens present on the surface of the red blood cells. Antigens are either salts or protein molecules whose structure is different in every individual because of genetic differences. These antigens sustain the structure of red blood cells, detect unwanted or disease-causing cells, and transport needed molecules into the cells and waste ones out of cells.
The composition and structure of four blood types are as follows:
- Group O: Group O red blood cells’ surface does not carry any antigens while the plasma consists of antibodies. A person with any ABO blood type can accept this blood type as no antigens are present while these people can accept only O blood type. This is the most common blood type with 63% of humans sharing it.
- Group A: A antigen is present on the surface of RBCs, and an anti-B antibody is present in plasma. Blood A people can donate to both A and AB types while they can accept only A group. About 21% of the population has this blood type.
- Group B: The red blood cells’ surface consists of B antigen, and the plasma has an anti-A antibody. Similar to A type of people, these also can donate blood to both A and AB blood groups, they can, however, accept only B type blood. This is the rarest blood type, only 16% of humanity has it.
- Group AB: The red blood cells have both A and B antigens, but the plasma does not contain any antibodies. People with type AB can take any ABO blood type. Their population is already included in A and B types.
Moreover, the red blood cells might have Rh factor or the RhD antigen. Rhesus grouping adds an extra dimension. A person is considered RhD positive if the red blood cells consist of the RhD antigen otherwise, they are RhD negative. A huge majority of the people in the world are known to have the Rh-positive blood type.
So, to wrap up, the ABO system is the best way to classify blood types. O positive is the most common, and AB negative is the rarest known blood group.