Hemocateresis: what it is, characteristics and operation

Erythrocytes or red blood cells are the most common cell types in the blood. Because they contain hemoglobin, these cells are responsible for transporting oxygen in the blood to the different types of tissues and organs in our body.

Having such an essential function, it is not surprising that there are about 5,000,000 erythrocytes per cubic millimeter of blood, that is, 1000 times more than the number of white blood cells.

These cells are very characteristic, since they lack a nucleus and mitochondria and, therefore, can only obtain energy through the breakdown of glucose. Their functionality is very limited, since they cannot synthesize proteins, which is why erythrocytes are considered, literally, as "hemoglobin sacs".

Hematopoiesis is the process by which these unique cell types are synthesized. This mechanism is well known in biological and medical fields, as it is one of the first pathways to be studied due to its physiological importance. Something much less widespread is, on the other hand, the process by which the "removed" red blood cells are eliminated. Today we tell you

all about hemocateresis or eryptosis. Do not miss it.

• Related article: "Main Cell Types of the Human Body"

What is hemocateresis?

From a simple physiological point of view, we can define hemocateresis as the process by which red blood cells (red blood cells) are eliminated in the process of degeneration at the level of the spleen and in the liver. These cell types have a half-life of 120 days and, when they age, they are destroyed by cellular apoptosis mechanisms.

We have introduced a striking term that is worth dwelling on: apoptosis. We can define this physiological process as a "programmed cell death", a set of biochemical reactions that occur in multicellular living beings so that the degenerate cell dies without causing any damage to the organization of the tissues to which it belongs.

The apoptosis process is completely normal because, without going any further, the epidermal cells are constantly changing. What is it but dandruff? Studies estimate that approximately 3,000,000 cells die in our body every second naturally, a value that increases with injuries or serious infectious processes such as necrotizing fasciitis.

In any case, erythrocytes, red blood cells or red blood cells (whatever you want to call them) are anything but normal cells. Therefore, we dedicate the following lines exclusively to elucidate how these aged entities end up disappearing from our body.

The fascinating process of eryptosis

As we have said before, human beings present a huge amount of red blood cells. per liter of blood, since these represent 10% of the total cell volume adding all our tissues. Circulating red blood cells have a half-life of 120 days, but are continually exposed to demanding factors at the physiological, such as oxidative stress that occurs in the lungs and hyperosmotic conditions when passing several times a day through the kidneys.

Thus, there comes a time when the "life" of these cell bodies is exhausted. Like any process that involves the presence of cells, their generation and replacement must be strictly regulated, which is why in many cases it is considered that the very genesis of erythrocytes involves partial apoptosis (since the nucleus and mitochondria are lost in their differentiation, for example). The fate of these cells is sealed from the start.

Let's keep things simple: when a red blood cell ages, a series of IgG immunoglobulin-like proteins (antibodies) bind to it. The function of these antibodies is to "signal" the aged red blood cell so that Kupffer cells in the liver can engulf them. The main molecular mechanisms involved that signal this “aging” of the erythrocyte are the following:

• The decrease in the energy charge of the circulating red blood cell.
• The decrease in the reducing power of the erythrocyte.
• Presence of osmotic stress.

Any of these 3 cellular mechanisms (or all 3 at the same time) are those that promote the event of hemocateresis, that is that is, that the senescent red blood cell itself is phagocytosed and is not re-incorporated into the blood circulating.

Once engulfed...

Once these red blood cells have been phagocytosed in the spleen, liver, and bone marrow, the hemoglobin is recycled. The “globin” portion, that is, the protein part, is recycled and broken down into amino acids that can be used for the synthesis of other essential molecules for the organism. The "heme" part; on the other hand, it is a non-protein prosthetic group, which is why it cannot be broken down into useful forms so easily.

So that, this “heme” group dissociates into iron and bilirubin, a last molecule that may sound close to more than one reader. Bilirubin is a waste product that is secreted by bile in its conjugated form, so we can say that it ends up being released in the duodenum by the digestion process. On the other hand, iron can be stored in the form of certain specific molecules or returned to the spinal cord, where it will once again become part of new red blood cells.

But not everything ends here. Bilirubin passes through the small intestine, but in the large intestine, bacterial colonies transform it into urobilinogen. Part of this compound is reabsorbed into the blood and excreted in the urine, while another part is excreted in feces (in the form of stercobilin), a pigment that gives this characteristic brown color to feces bowel movements.

After briefly following this route, we can see how the body does not get rid of anything that is not completely useless. Many of the components of the dead red blood cell end up being reused, while the bilirubin is released with the bile at the level of the duodenum, serving in turn as part of a precursor digestive. Of course, the perfect machinery of the human body leaves nothing to chance.

• You may be interested in: "Erythrocytes (red blood cells): characteristics and functioning"

Eryptosis VS Apoptosis

As you can imagine, the death of a red blood cell is very different from the senescence of a normal tissue cell. Typical events of apoptosis include nuclear condensation, DNA fragmentation, rupture of nuclear membranes, mitochondrial depolarization and many other events that cannot directly occur in red blood cells due to the lack of these structures.

Even so, it is necessary to take into account that both processes are relatively similar and that the purpose is common: to replace a group of cells whose useful life has come to an end.

Diseases associated with hemocateresis or eryptosis

Hemocateresis or eryptosis is not always a normal and programmed mechanism, since there are certain pathologies that can accelerate the death of red blood cells and their consequent degradation.

A clear example of this is malaria. More than 400,000 people die each year from this parasite (Plasmodium falciparum, mainly), which is transmitted to humans by the bite of infected mosquitoes and ends up spreading to the bloodstream and infecting blood cells reds. Once inside them, the pathogens multiply and encourage their premature rupture, which releases even more parasites into the blood to infect more red blood cells.

All this causes severe physiological disturbances that cause anemia, bloody stools, chills, sweating, seizures, headaches, and even coma and death. Without treatment, up to 40% of those infected end up dying. This is a clear example of what happens when unscheduled hemocateresis or eryptosis occurs on a massive scale and the danger that this entails.

Another less aggressive but equally important example is a lack of iron. A lack of iron in the body causes the "heme" part of hemoglobin to be smaller and less efficient, which is why the red blood cell sees its half-life reduced. From the entry of parasites into the body to a lack of nutritional intake, the half-life or senescence pattern of red blood cells in our body can be disrupted.

Summary

As you may have read in these lines, hemocateresis or eryptosis is a process that is divided into two important phases: signaling and phagocytosis. of the senescent red blood cell and the various metabolic pathways that its components follow until they end up being reused or excreted in the urine and/or stool.

If we want you to keep an idea of ​​all this biochemical conglomerate, it is the following: red blood cells are atypical cells, which is why their senescence process is different from that of a cell present in any normal tissue. Even so, the process of eryptosis and apoptosis seeks a specific purpose, eliminating cells that have ceased to be useful for the organism in order to replace them with new ones.

Bibliographic references:

• Escorza, M. TO. Q., & Salinas, J. v. c. (2006). Eryptosis, apoptosis of an erythrocyte. Biochemical Education Journal, 25(3), 85 - 89.
• Herlax, V., Vazquez, R., Mate, S., & Bakás, L. (2011). Eryptosis, the suicidal death of erythrocytes: mechanism and associated diseases. Latin American Clinical Biochemical Act, 45(2), 287 - 296.
• Malaria, Medlineplus.gov. Collected on December 25 in https://medlineplus.gov/spanish/ency/article/000621.htm#:~:text=La%20malaria%20es%20causada%20por, shape%20of%20pair%C3%A1sitos%2C%20called%20merozo%C3%ADtos.
• Manzur-Jattin, F., Moneriz-Pretell, C., Corrales-Santander, H., & Cantillo-García, K. (2016). Eryptosis: molecular mechanisms and their involvement in atherothrombotic disease. Colombian Journal of Cardiology, 23(3), 218 - 226.