Hemocateresis what it is, process and functions

The hemocateritis It is the series of events that take place to "remove" old red blood cells, something that occurs 120 days after being released into the bloodstream. It can be said that hemocateresis is the opposite of hematopoiesis, because the latter is the procedure by which red blood cells are formed.

Hemocateresis is a less well-known process than hematopoiesis, but it is no less important, since the normal physiology of the formation and destruction of red blood cells largely depends on the interaction between the two. Hemocateresis is divided into two main processes: destruction of red blood cells and "recycling of hemoglobin".

For this to happen it is necessary that a series of biological processes interact with each other, so that red blood cells can be degraded once they reach their natural lifespan..

Article index

• 1 Process 
  • 1.1 Apoptosis
  • 1.2 Network of sinusoidal capillaries
  • 1.3 Recycling of hemoglobin
• 2 Functions of hemocateresis
• 3 Differences between hemocateresis and hematopoiesis 
• 4 References

Process

Cells such as those of the skin or the mucosa of the digestive tract grow in a kind of "transporter band" along the epithelium until finally they detach (shed) and are released. Instead, red blood cells are released into the circulation where they remain free, exerting their function for about 120 days..

During this process, a series of highly specialized mechanisms prevent red blood cells from "escaping" from the blood vessels, being filtered into the urine, or diverting out of the bloodstream..

So, if the processes associated with hemocateresis did not exist, red blood cells could remain in the circulation indefinitely..

However, this does not happen; on the contrary, once they reach their lifespan, red blood cells are eliminated from the blood circulation due to the conjunction of a series of very complex processes that begin with apoptosis.

Apoptosis

Apoptosis or "programmed cell death" is the process by which a cell is destined to die within a certain time or once a certain function has been exerted..

In the case of red blood cells, lacking cell nuclei and organelles, the cell does not have the ability to repair damage to the cell membrane, a product of the degradation of phospholipids and the stress caused by circulation through kilometers of blood vessels.

Thus, as time passes, the cell membrane of the red blood cells becomes increasingly thin and fragile, to the point that it is no longer possible to maintain its integrity. So the cell literally explodes.

However, it does not explode anywhere. In fact, if this happens it would be a problem, since it could lead to blockages of the blood vessels. For this reason, there is a very specialized vascular network whose function is almost exclusively to destroy the old red blood cells that pass through..

Sinusoidal capillary network

It is the network of capillaries in the spleen and, to a lesser extent, the liver. In these richly vascularized organs there is a complicated network of increasingly thin and tortuous capillaries that force the red blood cells to twist and twist as they pass through..

In this way, only those cells with a sufficiently flexible cell membrane will be able to pass, while red blood cells with fragile membranes will break down and release their components - especially the heme group - towards the surrounding tissue, where the recycling process will take place..

Hemoglobin recycling

Once they are broken, the remains of the red blood cells are phagocytosed (eaten) by macrophages (specialized cells that abound in the liver and spleen), which digest the different components until they are reduced to their basic elements.

In this sense, the globin portion (protein) is broken down to the amino acids that compose it, which will later be used to synthesize new proteins..

For its part, the heme group decomposes until obtaining iron, part of which will become part of the bile as bilirubin, while another portion is bound to proteins (transferrin, ferritin) where it can be stored until it is needed in the synthesis of new molecules of the heme group.

Once all phases of hemocateritis are completed, the life cycle of the red blood cells is closed, making room for new cells and recycling the vital components of the red blood cells to be used again. 

Functions of hemocateresis

The most obvious function of hemocateresis is to remove red blood cells that have already reached their lifespan from circulation. However, this has implications that go further, such as:

- Allows a balance between the formation and elimination of red blood cells.

- Helps maintain the density of the blood, preventing too many red blood cells.

- It allows the blood to always be kept at its maximum oxygen transport capacity, eliminating those cells that can no longer perform their function optimally.

- Helps to keep iron stores stable in the body.

- Ensures that circulating red blood cells have the ability to reach every corner of the body through the capillary network.

- Prevents deformed or abnormal red blood cells from entering the circulation, as in the case of spherocytosis, sickle cell anemia and elliptocytosis, among other conditions associated with the production of altered red blood cells.

Differences between hemocateresis and hematopoiesis

The first difference is that hematopoiesis "makes" new red blood cells while hemocateresis "destroys" old or bad red blood cells. However, there are other differences to consider between the two processes..

- Hematopoiesis takes place in the bone marrow, while hemocateresis occurs in the spleen and liver.

- Hematopoiesis is modulated by hormones (erythropoietin), while hemocateresis is predetermined from the moment the erythrocyte enters circulation.

- Hematopoiesis requires the consumption of "raw materials" such as amino acids and iron to produce new cells, while hemocateresis releases these compounds to be stored or used later..

- Hematopoiesis is a cellular process that involves complex chemical reactions in the bone marrow, whereas hemocateresis is a relatively simple mechanical process.

- Hematopoiesis consumes energy; hemocateresis does not.

References

1. 1. Tizianello, A., Pannacciulli, I., Salvidio, E., & Ajmar, F. (1961). A quantitative evaluation of the splenic and hepatic share in normal hemocatheresis. Journal of Internal Medicine, 169(3), 303-311.
   2. Pannacciulli, I., & Tizianello, A. (1960). The liver as site of hemocatheresis after splenectomy. Medical minerva, 51, 2785.
   3. TIZIANELLO, A., PANNACCIULLI, I., & SALVIDIO, E. (1960). The spleen as the site of normal hemocatheresis. An experimental study. Il Progresso medico, 16, 527.
   4. Sánchez-Fayos, J., & Outeiriño, J. (1973). Introduction to the dynamic physiopathology of the hemopoiesis-hemocatheresis cellular system. Spanish clinical journal, 131(6), 431-438.
   5. Balduini, C., Brovelli, A., Balduini, C. L., & Ascari, E. (1979). Structural modifications in membrane glycoproteins during the erythrocyte life-span. Ricerca in clinic and in laboratory, 9(1), 13.
   6. Maker, V. K., & Guzman-Arrieta, E. D. (2015). Spleen. In Cognitive Pearls in General Surgery (pp. 385-398). Springer, New York, NY.
   7. Pizzi, M., Fuligni, F., Santoro, L., Sabattini, E., Ichino, M., De Vito, R.,… & Alaggio, R. (2017). Spleen histology in children with sickle cell disease and hereditary spherocytosis: hints on the disease pathophysiology. Human pathology, 60, 95-103.