Blood types: characteristics and compositions

Between 5 to 6 liters of blood circulate through the veins of an adultBut the slightest loss of this fluid can have fatal consequences. The cardiovascular system carries out essential tasks for the rest of the cells, such as the transport of nutrients and oxygen, as well as the removal of residual components from these.

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

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

• You may be interested: "Major cell types of the human body"

Components of blood

The blood is a substance made up 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 elimination. They carry hemoglobin, responsible for the characteristic red color of 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 cell fragments that circulate in the blood. Their function is to act in coagulation (stop blood circulation) and in the healing of broken blood vessels to minimize losses.

4. Plasma

It is 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 immune defense (immunoglobulin or antibodies) and coagulation (clotting factors). When clotting factors are removed, plasma is renamed serum.

• You may be interested: "Cerebrospinal fluid: composition, functions and disorders"

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 in front of her. The tool used by leukocytes (specifically B lymphocytes) is the manufacture of antibodies that bind to the antigen to mark it and facilitate the attack on it.

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

AB0 system

It is the first system discovered to differentiate blood groups, and today it remains one of the main ones. In this case, it is divided into four blood types: A, B, AB, and 0. The AB0 system was described by biologist Karl Landsteiner in 1901, earning him the Nobel Prize for 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 found 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 has antibodies against B, and vice versa, while in the case of AB this blood type does not offer problems (since it presents both classes), while the 0 (which has an absence of the mentioned carbohydrate) has both antibodies against A and against B. The higher mortality in blood transfusions 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 are divided into Rh positive or negative. This categorization is based on the presence (positive) or absence (negative) of a unique protein in the red blood cell membrane.

This criterion to demarcate blood types was also discovered by Landsteiner together with Alexander S. Wiener in 1940, and first described in Rhesus macaques; hence her name.

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

Importance in donating blood

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

Generally, 0- is the most demanded blood type, since it is known as the universal donor, as it can be used for any case of transfusion as it does not have any antigen (neither A, nor B, nor Rh +). However, people with 0- cannot receive blood except of the same type, because they have all the antibodies against the rest of the types.

ANDInstead, AB + has been called "the universal receptor", since it can receive any type of blood, as it does not present 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.