Blood is a complex liquid that contains different cell types (red & white blood cells), platelets and molecules, circulating in a liquid called plasma at a speed of 40 cm / seconds, or 1.44 km per hour, in our body (in big vessels and at an average heart rate).
At first, the blood carries gases such as dioxygen, O2, and carbon dioxide CO2. The dioxygen, freshly transferred from the pulmonary alveoli, lands in the blood to be distributed to all the cells, with the aim of allowing the production of their own energy from the molecules brought by our food (sugar, fat, etc.). Once the energy is produced, cells have waste, the CO2, which goes the other way until expired. These gases are carried by cells that we know well, the red blood cells. These cells are very particular because they do not contain DNA, but the so famous red pigment, a protein that contains iron and ensures the exchange of gas, the hemoglobin.
We have 4.5 to 6 million of red blood cells per ml of blood. The levels of red blood cells and hemoglobin are often measured during a blood test. Their decrease (anemia) or increase, are problematic. An insufficient oxygenation of the tissues (hypoxia), causes nausea, vertigo or tinnitus … and our body compensates it simply by increasing the number of red blood cells (this is called polycythemia), stimulated by the EPO.
Some athletes have used this molecule to increase the production of red blood cells. Since their oxygenation is normal, more oxygen reaches body’s cells, including the muscles, which produce more energy. But beware, this method is not without risk since an increase in the number of red blood cells makes the blood necessarily thicker and the heart must provide more effort to circulate it.
As you understand, the blood circulates gases but also a large variety of molecules … sugar, fat, alcohol, hormones, etc. Always with the purpose of allowing them to be transported from point A to point B. Consequently, the composition of our blood reflects our health, but also our habits, our life.
Take the example of, the so-called cholesterol, brought by our food and also produced by the liver. Despite its (bad) reputation, it is nevertheless essential to our health. It is indeed an important component of the membrane or envelope of our cells, allowing the synthesis of steroid hormones, including sex hormones, bile acids or vitamin D. However, its excess, in particular the “bad” cholesterol or LDL, is worrying. Indeed, its accumulation in the blood increases the risk of cardiovascular disease by forming plaques on the inner surface of our vessels, promoting the formation of clots that can cause obstructions/ischemia.
Today, more and more molecules are hunted down because their accumulation in the blood can be a sign of various diseases such as kidney disfunction, cancer or certain neurological diseases.
A, B, AB, O, O neg, B +, etc … we are all part of a group!
In the past, some people have recovered after a blood transfusion, but many others have unfortunately died. So much that in 1668, the Parliament of Paris prohibited this practice until the beginning of the twentieth century. In 1900, Karl Landsteiner, an Austrian doctor and biologist, showed that the mixture of various human bloods can lead to an agglutination, a kind of big clot. In our veins and arteries, these agglutinations/clots are obviously fatal.
Landsteiner discovered different types of red blood cells: A, B and C (group which will be renamed O). Eventually, this classification would be completed a few years later by the AB group.
Actually, there are molecules on the surface of red blood cells called agglutinogens. They are of two types: A or B.
Type A people have agglutinogens type A, people in group B have agglutinogens B, people in group AB have both types, and people in group O …….they do not have any.
But we also have agglutinins in our blood. These molecules are in fact antibodies, free in the plasma, which recognize the agglutinogens A or B …. When these antibodies which recognize, for example, the type A, are in contact with red blood cells of type A, it forms the famous agglutinations discovered by Landsteiner. This structure is big enough to clog the vessels and looks like the Brussels atomium where the balls are the red blood cells and the bars connecting them together, the agglutinogens.
No one, fortunately, has both agglutinins and agglutinogens recognizing each other. In fact, it is quite the opposite, the system is complementary. As shown as follows:
– Type A: agglutinogens A + agglutinins that recognize group B
– Type B: agglutinogens B + agglutinins that recognize group A
– Type AB: agglutinogens A and B, and therefore, to avoid accidents, no agglutinins.
– And finally group O is the opposite, no agglutinogen, but agglutinins that recognize both groups A and B.
Thus, to avoid any risk during a blood transfusion, it is better to carry out a transfusion with the blood of a person of his/her own group.
However, since the AB group does not have agglutinin, the people will never reject a transfusion. They are called universal acceptors. On the other hand, people in group O are universal donors. Actually, it’s not totally true. You have to be, more exactly, “O negative”, to be a universal donor. The term “negative” means Rh negative. The rhesus system works almost in the same way as blood groups except that those who are Rh negative (and do not have this factor on their red blood cells), do not have anti-Rh antibodies. These are produced only during a first contact, with blood from a person who is Rh positive.