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What is Blood? Blood is a viscous fluid, red in colour,flowing continuously in our body’s circulatory system. About 8% of the body weight of a healthy individual will consist of blood. There will be about 5 – 6 litres of blood in human body. Blood is made of a fluid called “Blood Plasma” which acts as a vehicle to carry many substances like:-
in addition to the following three types of Blood Cells:-
- Red Blood Cells (RBC’s):- which carry Oxygen(O2) from lungs to various body tissues and take back Carbon dioxide(CO2) from the cells and tissues to be sent out of body in the form of exhaled air.
- White Blood Cells (WBC’s):- which act as body Scavengers and Guards. They help in the Immune system of the body and act as defence forces of the body killing the bacteria or any other organisms entering the body.
- Tiny Platelets :-which help in the clotting and coagulation of blood; when we get injured and bleed, the bleeding will stop only after a few minutes. This stopping of bleeding is possible by a mechanism called clotting of blood in which platelets plays a very vital role.
Blood Group or Blood Type is determined, partly by the A/ B /O blood group antigens present in the red blood cells. A blood group is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of Red Blood Cells.
These antigens may be proteins, carbohydrates, glycol proteins or glycol lipids, depending on the blood group system, and some of these antigens are also present on the surface of other types of cells of various tissues. Several of these Red Blood Cell surface antigens, that stem from one allele or very closely linked genes, collectively form a blood group system.
There are two types of Blood Grouping:-
- ABO – grouping : In this group there are four categories:- A Group ,B Group, O Group and AB Group.
- Rh – grouping:- In the Rh – Group either the individual is Rh-positive, or Rh-negative. Rh is a factor called as Rhesus factor that has come to us from Rhesus monkeys.
Every human being will fall in one of the following eight groups:-
- A Positive or A Negative
- B Positive or B Negative
- O Positive or O Negative
- AB Positive or AB Negative
About 85% of all human beings have “RH positive” blood, because their red blood cells contain a substance called the “Rhesus blood factor”. Their positive blood contains a protein that can be linked to the Rhesus. The negative RH factor in human blood exists since over many thousand years. Geneticists generally observe that the RH-negative factor is a mutation of unknown origin.
Blood type ‘O’ is the most common of the blood groups. And ‘O’ negative, the universal donor blood, constitutes less than only 7% of the world’s population. Scientists have been trying to create a synthetic RH negative ‘O’ blood, for use in surgery and medical treatments, but they are unable to succeed. The reason is that, while the protein in the positive blood can be cloned, that in the negative blood cannot be cloned.
Blood group AB individuals have both A and B antigens on the surface of their RBCs, and their blood serum does not contain any antibodies against either A or B antigen. Therefore, an individual with type AB blood can receive blood from any group(Universal Recipient), with AB being preferable, but can donate blood only to another group AB individual.
Blood group A individuals have the A antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the B antigen. Therefore, a group A individual can receive blood only from individuals of groups A or O with A being preferable, and can donate blood to individuals of groups A or AB.
Blood group B individuals have the B antigen on their surface of their RBCs, and blood serum containing IgM antibodies against the A antigen. Therefore, a group B individual can receive blood only from individuals of groups B or O with B being preferable, and can donate blood to individuals of groups B or AB.
Blood group O, or blood group zero in some countries, individuals do not have either A or B antigens on the surface of their RBCs, but their blood serum contains IgM anti-A antibodies and anti-B antibodies against the A and B blood group antigens.
Therefore, a group O individual can receive blood only from a group O individual, but can donate blood to individuals of any ABO blood group (ie A, B, O or AB). If a blood transfusion is needed in a dire emergency, and the time taken to process the recipient’s blood would cause a detrimental delay, “O Negative blood” can be issued.
Related Reading: “Blood Donation”