Thrombopoiesis is the formation of

thrombocytes Platelets, also called thrombocytes (from Greek language, Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the Coagulation#Coagulation factors, coagulation factors) is to react to bleeding ...

(blood platelets) in the

bone marrow Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It is composed of hematopoietic ce ...

Thrombopoietin Thrombopoietin (THPO) also known as megakaryocyte growth and development factor (MGDF) is a protein that in humans is encoded by the ''THPO'' gene. Thrombopoietin is a glycoprotein hormone produced by the liver and kidney which regulates the pro ...

is the main regulator of thrombopoiesis. Thrombopoietin affects most aspects of the production of platelets. This includes self-renewal and expansion of

hematopoietic stem cell Hematopoietic stem cells (HSCs) are the stem cells that give rise to other blood cells. This process is called haematopoiesis. In vertebrates, the very first definitive HSCs arise from the ventral endothelial wall of the embryonic aorta within t ...

s, stimulating the increase of megakaryocyte progenitor cells, and supporting these cells so they mature to become platelet-producing cells. The process of Thrombopoiesis is caused by the breakdown of proplatelets (mature megakaryocyte membrane pseudopodial projections). During the process almost all of the membranes, organelles, granules, and soluble macromolecules in the cytoplasm are being consumed. Apoptosis also plays a role in the final stages of thrombopoiesis by letting proplatelet processes to occur from the cytoskeleton of actin.

Platelets

Platelets are formed by megakaryocytes and are present in the bloodstream for 5–7 days. Platelets are regulators of hemostasis and thrombosis. Platelets become active in the blood following vascular injury. Vascular injury causes platelets to stick to the cellular matrix that is exposed under the endothelium, form a platelet plug, and then form a

thrombus A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of c ...

. Platelets are essential in the formation of an occlusive thrombus and are the main target of preventing the formation of an arterial thrombus. Platelets are also important in innate immunity and regulating tumor growth and vessel leakage.

Megakaryocytes

The

megakaryoblast A megakaryoblast is a precursor cell to a promegakaryocyte, which in turn becomes a megakaryocyte during haematopoiesis. It is the beginning of the thrombocytic series. Development The megakaryoblast derives from a CFU-Meg colony unit of pluripot ...

is a platelet precursor that undergoes endomitosis to form megakaryocytes that have 8 to 64 nuclei. Megakaryocytes shed platelets into the bloodstream. β1-tubulin microtubules, which are found in megakaryocytes, facilitate this process of shedding platelets into the bloodstream. Megakaryocytes are precursor cells that are highly specialized. Megakaryocytes give rise to 1,000 to 3,000 platelets. Megakaryocytes function in the process of Thrombopoiesis by producing platelets and releasing platelets into the bloodstream. Megakaryocyte development is regulated mainly by thrombopoietin. IL-3, IL-6, and IL-11 also play a role in the development of megakaryocytes by working closely with thrombopoietin.

Thrombopoietin

Thrombopoietin is the main regulator in the process of thrombopoiesis. In the liver and renal tubular epithelial cells, thrombopoietin is constantly being produced. Platelets and platelet precursors clear and destroy the thrombopoietin that is produced so the concentration of plasma thrombopoietin levels and platelet and platelet precursor mass are inversely proportional. If there is less platelet mass present, less thrombopoietin is cleared, which causes an increase in free plasma thrombopoietin that stimulates thrombopoiesis.

References

Coagulation system Hematopoiesis {{cell-biology-stub