Q.If a person with 'B' blood group gets injured, then from which blood group person can he take blood, and why? OR The diagram below (shown in the original paper) shows the double circulatory system with parts labelled A, B and C. Write the names of these parts and write their function in the circulatory system.

Blood Groups: ABO and Rh Systems

Every red blood cell carries identity markers called antigens on its surface. Your immune system uses these markers to tell "self" from "foreign." If a foreign antigen shows up in your bloodstream, your plasma antibodies attack it. Blood grouping is simply a classification of which antigens a person's red cells carry, and the two systems that matter most clinically are the ABO system and the Rh system.

The ABO System

Two antigens define this system: A and B. Depending on which ones a person inherits, they fall into one of four groups.

The governing rule is that a person never carries an antibody against their own antigen — that would mean the immune system attacking its own blood cells. So a person with antigen A makes anti-B antibodies (ready to attack any B cells that enter), and a person with no antigens at all (group O) makes both anti-A and anti-B.

Working Out Transfusion Compatibility

• Group A (anti-B present) cannot accept B or AB blood, but can accept A or O.
• Group B (anti-A present) cannot accept A or AB blood, but can accept B or O.
• Group AB has no antibodies at all, so it can accept blood from any ABO group — the universal recipient.
• Group O carries both antibodies, so it can only accept O blood — but because its red cells carry no antigen for anyone else's antibodies to attack, it can donate to any group — the universal donor.

The Rh System

The Rh system centres on a single important antigen, the Rh (D) factor. A person is either:

• Rh-positive (Rh+) — carries the Rh antigen on the red cells, or
• Rh-negative (Rh-) — does not carry it.

Unlike the ABO system, an Rh-negative person is not born with anti-Rh antibodies. Those antibodies only appear after the person's immune system has actually been exposed to Rh-positive blood, through a transfusion or a pregnancy.

• An Rh-negative person should receive Rh-negative blood.
• An Rh-positive person can safely receive either Rh-positive or Rh-negative blood.

Combining Both Systems …