Thrombopoiesis

from Wikipedia, the free encyclopedia

As thrombopoiesis , thrombopoiesis or Thrombozytopoese is the process of formation of platelets (platelets) in the bone marrow . It is part of hematopoiesis or blood formation.

Cell differentiation

All preliminary stages of the blood cells arise from mesenchymal cells , which can initially differentiate into all blood cells and are therefore referred to as pluripotent stem cells . These can develop into myeloid or lymphatic stem cells. Once one of these developmental paths has been taken, the cell loses its ability to enter other developmental paths; it is then referred to as a unipotent stem cell , since only one cell row can develop from it.

The myeloid stem cells in platelet develops over megakaryoblasts and megakaryocytes for the platelets .

The life span of the platelets is 5–12 days. They are broken down in the spleen , liver and lungs .

Megakaryoblast

Thrombopoiesis in humans begins when the hemocytoblast (myeloid stem cell) develops receptors for the hormone thrombopoietin , which is produced by the liver and kidney. After these receptors have formed, the hemocytoblast becomes a new cell, the megakaryoblast . In response to thrombopoietin, the megakaryoblast now replicates its DNA repeatedly without any nucleus or cell division. The result is a huge cell with a diameter of up to 100 μm, a large, multi-lobed nucleus and multiple sets of chromosomes, the megakaryocyte. The megakaryoblast has an intense blue cytoplasm .

Megakaryocyte

Megakaryocytes are the largest bone marrow cells (on average 35–160 μm). A special characteristic of megakaryocytes is polyploidy . This means that these cells can repeatedly reproduce their DNA without subsequent cell division. This leads to cells that have a DNA content of up to 128 sets of chromosomes (n). In the course of maturation, from a stage of 8n (8 sets of chromosomes) fragmentation (constriction) of the polyploid cells occurs. The broken off cytoplasmic parts are called propellants. A megakaryocyte cell produces 6 to 8 propellants and each of these approx. 1,000 platelets, so that a total of approx. 4,000-8,000 platelets (blood platelets) can be formed per cell.

regulation

Thrombocytopoiesis is stimulated by the hormone thrombopoietin (also called thrombopoietin). It is the most important cytokine in thrombocytopoiesis and is continuously synthesized in the kidneys , liver and bone marrow and then taken up and broken down by the blood platelets and megakaryocytes. The thrombopoietin blood level correlates inversely proportionally with the amount of platelets and megakaryocytes. This means that a low thrombopoietin level results in high platelet counts and vice versa. It is assumed that the level of thrombopoietin depends on its uptake by the platelet cells, which happens via receptors.

Thrombocytopoiesis disorders lead to thrombocytopenia (lack of blood platelets) or thrombocytosis (overproduction of blood platelets). A permanent excess production of platelets (over 600,000 / μl) is called essential thrombocythemia .

Web links