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Blood types: characteristics and compositions

Blood types: characteristics and compositions

April 5, 2024

Between 5 to 6 liters of blood circulate through the veins of an adult , but the minimum loss of this liquid can have fatal consequences. The cardiovascular system carries out essential tasks for the rest of cells, such as transporting both nutrients and oxygen, as well as the removal of residual components of these.

In addition, blood is the means of transport that cells of the immune system can use to move quickly to a damaged area, and therefore the donation of this is crucial to treat patients, but as in the case of organ transplantation, certain requirements must be taken into account before receiving blood.

And is that There are different types of blood and not all are compatible between them . A poor reception of that substance generates a rejection reaction in the patient that can be fatal.


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Components of blood

The blood is a substance composed of four main elements :

1. Erythrocytes or red blood cells

Also called red blood cells , are cells responsible for the transport of oxygen from the lungs to the rest of the body, and in turn transport carbon dioxide from the cells to the lungs, for their elimination. They carry hemoglobin, responsible for the characteristic red color of the blood.

2. Leukocytes

Commonly known as white blood cells , it is a set of cells that are part of the immune system and that share the function of protecting the body against harmful agents.


3. Platelets or thrombocytes

They are cellular fragments that circulate in the blood. Their function is to act on coagulation (stop the circulation of blood) and in the healing of broken blood vessels to minimize losses.

4. Plasma

It is about the liquid part of the blood; It is basically made up of water and proteins. It provides a means of transport, in addition to participating in the immune defense (immunoglobulin or antibodies) and in coagulation (clotting factors). When the coagulation factors are eliminated, the plasma is called serum .

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Blood groups (blood types)

Blood types, or blood groups , are defined by a series of characteristics found on the surface of erythrocytes, such as proteins or carbohydrates, which in a foreign body can be recognized as an antigen.


The concept of antigen responds to any substance that the immune system can recognize as unknown , thus initiating a defensive response to it. The tool that leukocytes use (specifically B lymphocytes) is the manufacture of antibodies that bind to the antigen to mark it and facilitate the attack towards it.

With the joint observation of these antigens and antibodies, 32 systems have been identified to date that differentiate between different types of blood. Nonetheless, there are two the most known and used: the AB0 system and the Rh factor . But we must bear in mind that they are not the only ones, there are other systems such as MNS, Duffy or Diego.

AB0 system

It is the first system discovered to differentiate blood groups, and currently it remains one of the main ones. In this case, it is divided into four types of blood: A, B, AB, and 0 . The AB0 system was described by biologist Karl Landsteiner in 1901, which earned him the Nobel Prize in medicine in 1930.

This is based on the presence or absence of a carbohydrate in the cell membrane of erythrocytes. Although this is not exclusive to these cells, on the contrary, it is distributed in other types of cells, which is why it is also important in organ transplantation.

The incompatibility is due to the fact that A presents antibodies against B, and vice versa , whereas in the case of AB this type of blood does not present problems (since it presents the two classes), while the 0 (which has absence of the aforementioned carbohydrate) has both antibodies against A and against B. The highest mortality in transfusions of blood is due to failures in the identification of this blood group.

Rh Factor

It is the second most used system, and in this case the blood types they are divided into Rh positive or negative . This categorization is based on the presence (positive) or absence (negative) of an exclusive protein in the membrane of erythrocytes.

This criterion to demarcate blood types was also discovered by Landsteiner together with Alexander S. Wiener in 1940, and described for the first time in rhesus macaques; hence its name.

The incompatibility is because the negative type presents antibodies against the positive type , but it does not happen in reverse, that is, positive type can receive Rh negative blood.

Importance in blood donation

Blood types have a demographic distribution, the most common being type 0+, while the least common type is AB-. This is an important fact in the field of donation.

Generally, the 0- is the most demanded blood type, since he is known as the universal donor , to be able to be used for any transfusion case to have no antigen (neither A, nor B, nor Rh +). However, people with 0- can not receive blood except for the same type, because they have all the antibodies against the other types.

ANDn change, the AB + has been called "the universal receiver" , since it can receive any type of blood, by not presenting any of the antibodies against the rest. The downside is that you can only donate for people of the same type, because it presents all types of antigens.


Blood, Part 1 - True Blood: Crash Course A&P #29 (April 2024).


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