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Hemopoiesis, i.e. the process of hematopoiesis, is the result of extremely complicated and complex mechanisms. They include interactions between cells and the environment mediated by, inter alia, cytokines, adhesion molecules, and transcription factors. The essence of haemopoiesis is the formation of mature morphotic elements of blood from the stem cell.


    1. Hemopoiesis - differentiation
    2. Hemopoiesis - Erythropoiesis
    3. Hemopoiesis - granulocytopoiesis
    4. Hemopoiesis - thrombopoiesis
    5. Hemopoiesis - lymphoid tissue

Hemopoiesisthat ishematopoiesis- blood formation - under physiological conditionsin adultstakes place only in red bone marrow, including the hipbones, vertebrae, flatbones, and ribs. Other organs, such as the thymus, lymph nodes, and spleen produce lymphocytes.

Hemopoiesis in uterotakes place in the liver and spleen. After it is born in these organs, it is broken down and done in the bone marrow.

In the neonatal and early childhood period, the red marrow occupies the entire space of the bone cavities. It is equal in volume to the bone marrow of adults.

From the age of 4, the number of fat cells in the cavities of long bones increases, forming the yellow bone marrow.

Around the age of 20, red bone marrow is found only in the epiphyses of long bones, in the cavities of the bones of the skull, sternum, vertebral bodies, and ribs. However, after the age of 40, it accounts for only half of this content.

Hemopoiesis - differentiation

The process is gradual. In the initial stage, precursor cells of lymphopoiesis and myelopoiesis are formed.

Myelopoiesis involves the emergence of seven cell lines:

      • erythropoietic
      • megakaryopoietic
      • neutrophilopoietic
      • macrophagopoietic
      • eosinophilopoietic
      • basophilopoietic
      • mast cell

Lymphopoiesis, on the other hand, is a process that results in the formation of T, B, NK lymphocytes.

Hemopoiesis - Erythropoiesis

Erythropoiesis is the process by which the precursor cell of the red blood cell system is transformed, in which the erythrocyte is the final stage. The different stagesErythropoiesis include:

      • proerytroblasta
      • basophilic erythroblast
      • multi-pigment erythroblast (in which hemoglobin first appears)
      • eosinophilic erythroblast (this is the normoblast in which hemoglobin synthesis is complete)
      • reticulocyte - reticulocyte remains after removal of the testicle. The reticulocyte has the ability to penetrate the blood-marrow barrier, while the intensive synthesis of DNA, RNA and proteins is characteristic of proerythroblasts and erythroblasts

Regulatory factors play an important role in the process of erythropoiesis:

      • erythropoietin
      • IL-3

and cell surface receptors that respond to them.

Hemopoiesis - granulocytopoiesis

Granulocytes are produced in the bone marrow. They are formed from the myeloid cell of the stem, common to erythrocytes, thrombocytes, monocytes, eosinophils and basophils.

More diverse forms are derived from the parent cell of the granulocytic system:

      • mieloblasty
      • myelocytes
      • metamelocytes

The time it takes for myeloblast to turn into mature granulocytes is approximately 7-10 days. Only mature rod-shaped and segmented granulocytes pass into the peripheral blood.

Hemopoiesis - thrombopoiesis

Thrombopoiesis is the process of the formation of platelets. Thrombocytes arise directly from megakaryocytes, the largest cells found in the bone marrow.

Megakaryocytes are produced by the process of stem cell differentiation through the megakaryoblast stage. Megakaryocytes are multinucleated cells, they mature for 3 days.

The resulting thrombocytes are characterized by the lack of a cell nucleus. The survival time of thrombocytes in peripheral blood is 7-10 days.

Interleukins are essential factors that stimulate thrombopoiesis

      • IL-3
      • IL-6
      • IL-9
      • IL-11
      • GM-CSF
      • erythropoietin and others

The inhibitor is the transforming growth factor beta-TGF-β and interferons.

Hemopoiesis - lymphoid tissue

      • central lymphoid tissue is bone marrow and thymus
      • peripheral lymphatic tissue includes lymph nodes, lymph nodes, spleen

These sites are where lymphopoiesis takes place - the maturation and proliferation of the cells of the lymphatic system. The precursor cells are derived from a common stem cell.

The first stages of B-cell maturation take place in the bone marrow.

The process startsstarts with a pre-pro-B cell, a progenitor B cell, a precursor B cell and an immature B cell.

During lymphocyte differentiation, specific surface antigens and receptors are expressed, on the basis of which the different stages of lymphopoiesis are determined.

The maturation of T lymphocytes is similar. Initially, the lymphoid precursor cell changes into protymocytes that travel from the bone marrow to the thymus.

The thymus becomes a key site in the maturation of the next stages of T cells.

The next steps in this lineage include early pre-T and late pre-T lymphocytes. This is followed by the formation of CD4 + helper T lymphocytes and CD8 + cytotoxic suppressor T lymphocytes.

Lymphopoiesis begins in the marrow and ends in the peripheral lymphopoietic organs.

    • T-lymphocyte → bone marrow → thymus → lymph node
    • Lymphocyte B → bone marrow → lymph node

When the bone marrow is unable to fulfill its hematopoietic function, for example due to fibrosis, the process of haemopoiesis can take place in the liver and spleen.

Usually, this production is not sufficient for the body.

The spleen and liver do not have a structure similar to that of the blood-marrow barrier.

About the authorNatalia MłyńskaStudent of medicine at the Medical University of Lodz. Medicine is her greatest passion. He also loves sports, mainly running and dancing. She would like to treat her future patients in such a way as to see them as a human being, not only a disease.

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