How Does the Rh Blood Group System Affect Blood Transfusion?
All the living cells in the human body require a constant supply of nutrients, oxygen and other essential substances. Also for the healthy functioning of the body and the tissues, the wasteful substances needed to be removed constantly. Therefore a mechanism is a must that helps in transporting nutrients and other substances from one cell to another. In simple organisms, water is present as a means of transport. But in complex organisms, blood is the commonly used body fluid. The lymph can also serve special purposes in transporting some nutrients. As blood is present in human beings, this blood in every individual is not the same. It has certain factors that make the blood different. On the types of antigens present on the red blood cells, there is an Rh blood group and an abo blood group. We will study more about the Rh blood group system below. First, let us learn about blood.
Blood
It is specialized connective tissue. It consists of a fluid matrix, plasma and also has formed elements that form the cellular portion. Plasma makes 55% of the blood and the rest 45% is made up of formed elements. Plasma is the fluid that forms the matrix of the blood. It is straw coloured. The plasma is composed of water, proteins, minerals and other amino acids. The water makes 90% of the plasma. Fibrinogen, globulin and albumins are the proteins that are present in plasma. Fibrinogen helps in the clotting of blood. Globulins help in the defence mechanism of the body and albumins help to maintain the osmotic balance. Glucose, amino acids and lipids are also present in the plasma and these substances enter and leave the plasma at regular intervals. The formed elements that make the rest of the composition are erythrocytes, leukocytes and platelets. Erythrocytes are the red blood cells that give blood its red colour and also help in transporting oxygen from one cell to another. The leukocytes are the white blood cells and they are known as soldiers of the body. They are named so because they help in fighting the body with infections. The leukocytes are lymphocytes, monocytes, eosinophils, basophils and neutrophils. The platelets in the blood are colourless and non-nucleated fragments of the cells. They are produced by the bone marrow and help in blood clotting.
Blood Group
Antigens are the molecules that are present on the surface of cells and thus they are recognised as foreign cells by the immune system and thus they can induce an immune response. To counter these antigens, the human body produces certain chemicals to fight against them and destroy them. These are known as antibodies. They get bonded to the antigens in a special fashion. The membranes of the red blood cells also contain some antigens. The ABO and Rh blood group system is done on this basis only.
Rh System
Rh blood group discovered by Karl Landsteiner. Rh in Rh blood group stands for Rhesus monkey. They are named so because they were first discovered in monkeys. The Rh system is a group of antigens that are present on the red blood cells. The people that possess these Rh system factors are known as Rh blood group positive and the people that do not have these factors are known as Rh blood group negative. A person that has Rh-ve factors, when exposed to Rh+ve blood, then it will form antibodies against the Rh antigen. Therefore Rh factors should also be taken care of when matching blood groups are taking place. In the Rh blood group system, Rh compatibility is also taken care of. This condition is observed when the Rh- blood of a mother who is pregnant with an Rh+ foetus. As the Rh- a mother is not exposed to Rh antigen of the foetus in her first pregnancy because the placental barriers keep a check on that but at the time of birth, there is a possibility of slight mixing of blood. When this happens the mother’s body makes appropriate antibodies to fight it. And these antibodies can cross the placenta and then if the same condition happens in the second pregnancy, they can destroy the foetus as this foetus for the mother’s cells is foreign. Erythroblastosis foetalis is the name of this condition.
ABO Grouping
Karl Landsteiner gave this system in 1901. This blood group is based on the presence and absence of two surface antigens which are A and B and are present on the RBC. The individual plasma also contains anti-A and anti-B antibodies. According to him, if an antigen is present in the blood then its corresponding antibody will be present in the individual. Also, if the antigen is absent in the RBC, then the antibody must be present in the plasma. To its own antigens of red blood cells, the immune system exhibits tolerance. So a person who has an A blood group will have B antibodies and not A-antibodies. The same applies to the B blood group. For the AB blood group, no antibodies are produced and for the O-blood group, both the antibodies that are anti-A and anti-B are present.
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FAQs on Rh Blood Group System: Definition, Inheritance & Role
1. What is the Rh blood group system?
The Rh blood group system is the second most important blood group system after the ABO system. It is named after the Rhesus monkey, where it was first discovered. This system classifies blood based on the presence or absence of a specific antigen, known as the Rh factor or D antigen, on the surface of red blood cells (RBCs).
2. What is the difference between Rh-positive and Rh-negative blood types?
The primary difference lies in the presence or absence of the Rh antigen on the red blood cells.
- Rh-positive (Rh+): Individuals whose RBCs have the Rh antigen on their surface are called Rh-positive. The majority of the human population is Rh-positive.
- Rh-negative (Rh-): Individuals whose RBCs lack the Rh antigen are called Rh-negative. These individuals can produce anti-Rh antibodies if they are exposed to Rh+ blood.
3. How is the Rh factor inherited from parents?
The Rh factor is inherited as a dominant trait. The gene for the Rh factor has two alleles: 'R' (dominant, produces Rh factor) and 'r' (recessive, does not produce Rh factor). An individual can have one of three genotypes:
- RR (homozygous dominant): Rh-positive
- Rr (heterozygous): Rh-positive
- rr (homozygous recessive): Rh-negative
4. Why is the Rh factor important in blood transfusions?
Rh factor is critical for ensuring compatibility in blood transfusions. If an Rh-negative person receives Rh-positive blood, their immune system will recognise the Rh antigen as foreign and start producing anti-Rh antibodies. While the first transfusion might not cause a severe reaction, subsequent transfusions with Rh-positive blood can lead to a severe, potentially fatal, transfusion reaction where the recipient's antibodies attack and destroy the donor's RBCs (hemolysis).
5. What is erythroblastosis fetalis and how does Rh incompatibility cause it?
Erythroblastosis fetalis is a severe hemolytic disease of the newborn. It occurs due to Rh incompatibility between an Rh-negative mother and her Rh-positive fetus. During the delivery of the first Rh-positive child, some of the fetus's blood can enter the mother's bloodstream, causing her to develop anti-Rh antibodies. In a subsequent pregnancy with another Rh-positive fetus, these maternal antibodies can cross the placenta and attack the fetus's red blood cells, leading to severe anemia, jaundice, and potential brain damage or death of the fetus or newborn.
6. Why is an Rh-negative mother's second Rh-positive pregnancy at a much higher risk than the first one?
The first Rh-positive pregnancy is usually unaffected because the mother's and fetus's blood systems are separated by the placenta. The sensitisation, or development of anti-Rh antibodies in the mother, typically occurs at the time of delivery when placental tearing allows fetal RBCs to mix with maternal blood. By the time the mother has produced a significant number of antibodies, the first baby has already been born. However, these antibodies persist in her system, creating a 'memory'. For the second Rh-positive pregnancy, these pre-existing antibodies can immediately cross the placenta and attack the fetus's blood cells from early on, causing significant harm.
7. How is Rh incompatibility managed or prevented during pregnancy?
Rh incompatibility can be effectively managed by administering an injection of Rho(D) immune globulin (RhoGAM) to the Rh-negative mother. This injection contains anti-Rh antibodies that find and destroy any Rh-positive fetal cells in the mother's bloodstream before her immune system can produce its own antibodies. It is typically given around the 28th week of pregnancy and again within 72 hours after the birth of an Rh-positive baby. This prevents the mother from becoming sensitised, thereby protecting future pregnancies.
8. Who discovered the Rh blood group system?
The Rh blood group system was discovered in 1940 by scientists Karl Landsteiner and Alexander S. Wiener. They identified the Rh antigen by injecting red blood cells from Rhesus macaque monkeys into rabbits and guinea pigs, which then produced an antibody that also reacted with the red blood cells of a large percentage of the human population. This is why it is named 'Rh' for 'Rhesus'.
