Hemocateresis: what it is, characteristics and how it works
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.
With 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 nuclei 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 literally considered “hemoglobin sacks”.
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 routes to be studied due to its physiological importance. Something much less widespread is, on the other hand, the process by which the red blood cells “removed” are eliminated. Today we tell you all about hemocateresis or eryptosis. Do not miss it.
What is hemocateresis?
From a simple physiological point of view, we can define hemocateresis as the process by which degenerating red blood cells (red blood cells) are eliminated in the spleen and in the liver. These cell types have a half-life of 120 days and, as they age, they are destroyed by mechanisms of cellular apoptosis.
We have introduced a catchy term that is worth stopping at: apoptosis. We can define this physiological process as a “programmed cell death”, a set of biochemical reactions that occur in multicellular living beings in order for the degenerated cell to die 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, value that is increased in the face of injuries or serious infectious processes such as necrotizing fasciitis.
Erythrocytes, red blood cells or red blood cells (whatever you want to call them) are anything but normal cells anyway. For this reason, we dedicate the following lines exclusively to elucidate how these aging entities end up disappearing from our body.
The fascinating process of eryptosis
As we have said before, human beings present an enormous amount of red blood cells per liter of blood, since these represent 10% of the total cell volume adding all our tissues. Circulating erythrocytes have a half-life of 120 days, but they are continuously exposed to physiologically demanding factors, such as oxidative stress that occurs in the lungs and hyperosmotic conditions when they pass through the kidneys several times a day.
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 the genesis of erythrocytes itself is considered to be a 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: As an erythrocyte 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 the 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 load of the circulating red blood cell.
- The decrease in the reducing power of the erythrocyte.
- Presence of osmotic stress.
Some of these 3 cellular mechanisms (or all 3 at the same time) are those that promote the event of hemocateresis, that is, that the senescent red blood cell itself is phagocytosed and is not re-incorporated into the circulating blood.
Once engulfed …
Once these red blood cells have been engulfed in the spleen, liver, and bone marrow, the hemoglobin is recycled. The “globin” portion, that is, the protein part, is recycled and decomposed into amino acids that can be used for the synthesis of other essential molecules for the body. The “heme” part; on the other hand, it is a prosthetic group not made up of proteins, which is why it cannot be decomposed 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 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 become part of new red blood cells.
But not everything ends here. Bilirubin passes through the small intestine, but in the large intestine it is transformed by bacterial colonies into urobilinogen. Part of this compound is reabsorbed into the blood and excreted in the urine, while another part is excreted in the feces (in the form of stercobilin), a pigment that gives stools this characteristic brown color.
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 digestive precursor. Of course, the perfect machinery of the human body leaves nothing to chance.
Eryptosis VS apoptosis
As you can imagine the death of a red blood cell is very different from the senescence of a cell in normal tissue. 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 cells due to the lack of these structures.
Even so, it is necessary to bear in mind 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 advance the death of red blood cells and their consequent degradation.
A clear example of this is malaria. More than 400,000 people die annually from this parasite (Plasmodium falciparum, mainly), which is transmitted to humans by the bite of infected mosquitoes and ends up spreading into the bloodstream and infecting red blood cells. Once inside them, the pathogens multiply and lead to their premature breakdown, releasing even more parasites into the blood to infect more red blood cells.
All this causes severe physiological imbalances causing 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 massively unscheduled hemocateresis or eryptosis occur 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 makes the “heme” part of hemoglobin smaller and less efficient, which is why the red blood cell has a reduced half-life. From the entry of parasites into the body to a lack of nutritional intake, the half-life or the pattern of senescence of red blood cells in our body can be disrupted.
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 routes that its components follow until they end up being reused or excreted in the urine and / or stool.
If we want you to have an idea of this entire 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, to eliminate cells that are no longer useful for the body to replace them with new ones.
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- Malaria, Medlineplus.gov. Retrieved December 25 from https://medlineplus.gov/spanish/ency/article/000621.htm#:~:text=La%20malaria%20es%20causada%20por,forma%20de%20par%C3%A1sitos%2C % 20call% 20merozo% C3% ADtos.
- Manzur-Jattin, F., Moneriz-Pretell, C., Corrales-Santander, H., & Cantillo-García, K. (2016). Eryptosis: molecular mechanisms and their implication in atherothrombotic disease. Colombian Journal of Cardiology, 23 (3), 218 – 226.