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Blood is a fluid connective tissue that is the most important component of the circulatory system. Approximately 5 liters or 12 pints of blood circulates throughout the body of a healthy person. The composition of blood includes erythrocytes, platelets, and leukocytes suspended in plasma along with millions of different molecules having their own roles and functions. Even though the components of blood are similar for all humans, there are various blood types or groups. There are more than 40 blood groups, though not all of them are clinically significant. The discovery of the ABO blood group had created great excitement and from then all the blood had been assumed to be the same.
| Table of Contents |
Key Terms: Blood Group System, Blood, Plasma, Platelets, ABO group system, Rh blood group system, blood transfusion
Blood Group System
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Red blood cells (RBCs), white blood cells (WBCs), and platelets are all present in a liquid known as plasma. The blood type of a person is identified by the antibodies and antigens in the blood. Antibodies are the proteins present in the blood which are a natural aspect of the defense system of the body. They are able to identify foreign things like pathogens. They notify the immune system of a person which works to eliminate them. Antigens are the protein molecules that are located on the surface of the red blood cells.
The ABO blood group system was discovered in the year 1900 by an Australian scientist named Karl Landsteiner. He mixed different types of blood in his experiment and observed that the plasma from certain blood types formed clusters or produced agglutinates that were caused due to the absence of red blood cell molecules. He then observed the agglutination and divided blood into 4 different groups. He was also awarded the Nobel Prize for his discovery.
- The blood group system plays an important role in blood transfusion.
- Our immune system identifies blood of another type as a foreign agent and attacks it if it is introduced into the body causing a transfusion reaction.
- Any inappropriate match with the ABO and Rh blood types can lead to the most serious and life-threatening transfusion reactions.
- Hence, it is suggested to have the blood group checked before blood transfusion.
What are ABO and Rh blood groups?
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The blood grouping system is the genetically determined system through which blood can be classified into various groups as per the presence or absence of antigens or agglutinogen on the surface of the Red Blood Cells and the antibodies in the plasma. During a blood transfusion, the ABO system and the Rhesus system are the two most important group systems that are examined.
The ABO blood group system has 4 types of blood groups namely A, B, AB, and O. It is mainly based on the antibodies and antigens on the red blood cells and in the plasma. Antigens and antibodies both are the protein molecules in which the antigens are present on the surface of the RBCs or the Red Blood Cells. The antibodies are present in the plasma that is involved in the defense mechanisms.
The Rhesus blood group system or the Rh blood group system has 50 defined blood group antigens. The most important antigens in the Rh group system are D, C, c, E, and e.
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ABO blood group system
ABO grouping is done on the basis of two antigens - Antigen A and Antigen B. The ABO grouping system is classified into 4 types on the basis of the presence or absence of antigens on the surface of the red blood cells and plasma antibodies.
- Group A has antigen A and antibody B.
- Group B has antigen B and antibody A.
- Group AB has both A and B antigens and no antibodies (neither A nor B).
- Group O has neither A nor B antigens and both antibodies A and B.
| Blood Group | Antigens on RBCs | Antibodies in Plasma |
|---|---|---|
| A | A | anti B |
| B | B | anti A |
| AB | A and B | Nil |
| O | Nil | anti A and anti B |
As the mismatch of the blood groups during blood transfusion can lead to clumping of RBCs along with various other disorders, the ABO blood group system is important during blood donation.
- It is important for blood cells to match while donating blood which means that donor-recipient compatibility is needed.
- For instance, a person of blood group A can receive blood from either group A or group O as there are no antibodies for A and O in blood group A.
- The individuals with blood group O are known as universal donors. Individuals with blood group AB are called universal recipients.
Do Check Out:
| Important Concepts | ||
|---|---|---|
| Blood Group Test | Blood Coagulation | Body Fluids and Circulation |
| Double Circulation | Diagram of Heart | ECG |
| Heart Diseases | Pulmonary Hypertension | High Blood Pressure |
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Rh Blood Group System
The Rh blood group system is another prominent blood group system in addition to the ABO group system.
- Over two-thirds of the population has the third antigen on the surface of the red blood cells which is known as the Rh factor or Rh antigen.
- This antigen decided whether the blood group of the person is positive or negative.
- If the Rh factor is there, the individual is Rhesus positive (Rh +ve).
- In the absence of the Rh factor, the individual is Rhesus negative (Rh -ve) as they produce antibodies.
- Hence, in this case, as well, the compatibility of blood groups between the donor and recipient is necessary.
Things to Remember
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- Blood is a fluid connective tissue formed of erythrocytes, platelets, and leukocytes suspended in plasma.
- The blood grouping system is the genetically determined system through which blood is classified into various groups.
- The blood is grouped as per the presence or absence of antigens or on the surface of RBCs and the presence or absence of antibodies in the plasma.
- As per the ABO blood group system, the blood groups can be classified as A, B, AB, and O.
- As per the Rh blood group system, the blood group is classified as Rhesus positive (Rh +ve) and Rhesus negative (Rh -ve).
Previous Year Questions
- Splenic artery arises from… [NEET 1991]
- The life span of human WBC is approximately… [NEET 1997]
- The most active phagocytic white blood cells are… [NEET 2008]
- RA - Right Auricle RV - Right Ventricle LA - Left Auricle LV - Left Ventricle in the… [KCET 2007]
- Study the diagram given below and identify the cells labeled as A, B, C, and D… [KCET 2012]
- The largest RBC's have been seen in… [KCET 2007]
- Heparin is secreted by…
- RBCs are nucleated in…
- The vitamin which is essential for blood clotting is…
- The condition of erythroblastosis foetalis occurs only when… [JKCET 2007]
Sample Questions
Ques. What are red blood cells? (5 marks)
Ans. Red Blood Cells are human biconcave and nucleus-free cells. They are also known as erythrocytes. Haemoglobin, the iron-rich protein, is found in RBCs which gives it its red color.
- RBCs are the most abundant cells that are formed in the bone marrow.
- Hemoglobin mostly consists of iron, mixed with oxygen, which gives the blood its red color.
- RBC involves transporting oxygen to different organs and tissues in the human body.
- They have a lifetime of 100 to 120 days.
- RBC extracts carbon dioxide to be replenished in the lungs from different organs and tissues.
Ques. What are the functions of blood? (5 marks)
Ans. The functions of blood are -
- It delivers nutrition and oxygen to the lungs and tissues.
- It creates blood clots to prevent the loss of excessive blood.
- It has antibodies and cells that fight against infection.
- It controls the body temperature.
- Blood delivers waste products to the liver and kidneys which then purify and filter the blood.
Ques. What is the significance of identifying one’s blood groups? (3 marks)
Ans. The blood group’s identification is significant as -
- A blood group test helps an individual identify his or her blood group.
- It helps in the proper blood transfusion.
- Couples also plan pregnancy knowing the blood group to avoid chances of erythroblastosis foetalis.
Ques. Write a short note on blood clotting. (3 marks)
Ans. Blood clotting, also known as haemostasis, refers to the formation of a clot or a gel-like structure that prevents the excessive loss of blood, i.e., haemorrhage in cases of blood vessels being injured.
- The gel or a clot has a network of insoluble protein fibers known as fibrin in which the formed elements of blood get trapped.
- Blood clotting has a series of chemical reactions that results in the formation of a fibrin network.
Ques. What are antibodies and antigens? (3 marks)
Ans. Blood is formed of red blood cells, white blood cells, and platelets in a liquid known as plasma. The blood group of a person is identified by antibodies and antigens in the blood.
- Antibodies are the proteins present in plasma. They are a part of the natural defense system of the body. They identify foreign substances and alert the immune system, which destroys them.
- Antigens are protein molecules that are found on the surface of RBCs.
Ques. On the basis of the ABO and Rh group system, how many types of blood groups are there? (3 marks)
Ans. The 8 types of blood groups are -
- A RhD positive (A+)
- A RhD negative (A-)
- B RhD positive (B+)
- B RhD negative (B-)
- AB RhD positive (AB+)
- AB RhD negative (AB-)
- O RhD positive (O+)
- O RhD negative (O-)
Ques. What are the conditions for blood donation? (3 marks)
Ans. In order to be eligible for blood donation, one must
- Be fit and healthy.
- Weigh at least 50 kg.
- Be between 17 to 66 years old or are over 70 and have been given blood in the last 2 years.
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