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From left to right: erythrocyte (red blood cell), activated platelet and leukocyte (white blood cell) in the scanning electron microscope
Discoid, inactive platelets on the left, activated platelets with pseudopodia on the right .

Thrombocytes or thrombocytes ( singular of the thrombocyte ; from ancient Greek θρόμβος thrómbos "lump" and ancient Greek κύτος kýtos "cavity", "vessel", "envelope") or platelets are the smallest cells in the blood . They play an important role in blood clotting by attaching themselves to the surrounding tissue (" platelet adhesion ") or sticking together (" platelet aggregation ") when a blood vessel is injured , so that the injury is closed. In addition, they release substances that promote coagulation.

Platelets have neither nuclei nor genetic information ( DNA ). They are caused by pinching off megakaryocytes that are located in the bone marrow .

Structure and function

Platelets are created in the bone marrow, where they are pinched off by megakaryocytes, huge platelet-forming cells. Up to 8000 platelets can be cut off from such a bone marrow cell in the course of a lifetime. This process is called thrombopoiesis and is supported by the hormone thrombopoietin .

Platelets have a diameter of 1.5 µm to 3.0 µm and are flat like a disk ( discoid ). During blood clotting, platelets change their shape due to activators such as ADP , collagen , thromboxane and thrombin . The protuberance of pseudopodia takes place , which is accompanied by a multiple increase in surface area. This promotes thrombus formation through fibrin-mediated binding with other platelets. This process describes the function of platelets and is called platelet aggregation .

In healthy people, a platelet count between 150,000 and 450,000 per µl of blood is considered normal. The platelet concentration is genetically determined and varies little over the lifetime of a healthy adult. In a healthy population, the platelet concentration follows a normal distribution .

The average lifespan of platelets is eight to twelve days. The breakdown takes place mainly in the spleen , in which a third of the platelets are also temporarily stored, as well as in the lungs and, to a lesser extent, in the liver .

Cellular Aspects

Despite the lack of a cell nucleus, mRNA from megakaryocytes was found in platelets . They are therefore capable , albeit to a limited extent, of the new synthesis of proteins . Like other cells , they have mitochondria , but a special form of the rough endoplasmic reticulum (rER), the canalicular system. It serves as a calcium ion store, the rapid emptying of which into the cytosol is an essential prerequisite for physiological platelet aggregation . The storage granules are important as further compartments in platelets : They are divided into α-granules, electron-dense granules and lysosomes and contain substances and proteins that promote aggregation , the secretion (release) of which is necessary for platelet function. The plasma membrane of platelets contains among other things the protein tissue factor (engl. Tissue factor ). It is assumed that vesicles with this protein constrict themselves and can now be found as circulating microparticles in the blood. This ability, which they have in common with monocytes , helps blood to clot .

Enlargement of the spleen ( splenomegaly ) or immune thrombocytopenia lead to a reduction in the average platelet life, which leads to an overall low platelet concentration with a constant production rate. Conversely, after removal of the spleen ( splenectomy ) there is a sharp increase in the number of platelets due to the lack of spleen-mediated breakdown.

Platelet pathology

There are three types of disturbance or abnormality in platelets. A distinction is made between primary (mostly genetic) deviations, which are sometimes also called idiopathic or essential, and secondary deviations due to another underlying disease or disorder. The three types of deviation are:

  • Thrombocytopenia : Decreased concentration of platelets in the blood with values ​​below 150,000 / µl. Below 80,000 / µl an increased tendency to bleeding is to be expected, below 50,000 / µl it can lead to spontaneous bleeding ( nosebleeds , bruises ). Concentrations below 10,000 / µl must be closely monitored if medically necessary and, if necessary,treatedwith platelet concentrates .
    Causes can be a reduced formation, an increased breakdown or consumption. Primary, genetic causes of thrombocytopenia are e.g. b. TAR syndrome , Wiskott-Aldrich syndrome , Jacobsen syndrome or Gaucher's disease . Thrombocytopenia can occasionally occur even with drug therapy, and
    heparin-induced thrombocytopenia causedby heparin or other low-molecular-weight heparinsis considered very rare but very dangerous. During pregnancy , the number of platelets in the blood is often low. About 5–10% of pregnant women have fewer than 150,000 platelets / µl. If values ​​are below 100,000 / µl, causes other than pregnancy or a pregnancy complication should be considered.


Presumably, thrombocytes were described for the first time in 1844 by Alfred Donné (1801–1878) as “globules” in blood plasma (De l'órigine d. Glob. Du sang etc. Comptes rend. Soc. Biolog. 1844, t. XIV). In 1865, Max Schultze described them much more precisely in the archive for microscopic anatomy , but did not recognize them as a separate type of cell, but instead considered them to be degradation products. Giulio Bizzozzero corrected this mistake in 1883 and was the first to recognize the role of platelets in blood clotting.

Economic application

The lysate from (donor) platelets is used in human cell culture as a nutrient additive ( human platelet lysate ).

See also


  • R. Degkwitz: Studies on blood platelets in Folia Haematologica Leipzig 1920, XXV, p.153
  • DB Brewer: Max Schultze (1865), G. Bizzozero (1882) and the discovery of the platelet. In: Br J Haematol . 133 (3), 2006 May, pp. 251-258. PMID 16643426
  • S2k guideline thrombocytopathies of the Society for Thrombosis and Haemostasis Research (GTH). In: AWMF online (as of 2012)

Web links

Wiktionary: Thrombocyte  - explanations of meanings, word origins, synonyms, translations
Commons : Platelets  - Collection of pictures, videos and audio files

Individual evidence

  1. ^ Wilhelm Gemoll: Greek-German school and hand dictionary. Munich / Vienna 1965.
  2. Jessica A. Reese, Jennifer D. Peck, David R. Deschamps, Jennifer J. McIntosh, Eric J. Knudtson, Deirdra R. Terrell, Sara K. Vesely, James N. George: Platelet Counts during Pregnancy New England Journal of Medicine 2018, Volume 379, Issue 1 of July 5, 2018, pages 32–43, DOI: 10.1056 / NEJMoa1802897
  3. N. Mackman: Role of tissue factor in hemostasis and thrombosis. In: Blood Cells Mol Dis. 36 (2), 2006 Mar-Apr, pp. 104-107. Review.
  4. ^ F Boehlen, P Hohlfeld, P Extermann, TV Perneger, P de Moerloose .: Platelet count at term pregnancy: a reappraisal of the threshold. In: Obstet Gybecol . tape 95 , no. 1 , 2000, pp. 29-33 .
  5. Platelet Counts during Pregnancy | NEJM. Retrieved December 21, 2018 .
  6. Barbara I. Tshisuaka: Donné, Alfred. In: Werner E. Gerabek , Bernhard D. Haage, Gundolf Keil , Wolfgang Wegner (eds.): Enzyklopädie Medizingeschichte. De Gruyter, Berlin / New York 2005, ISBN 3-11-015714-4 , p. 322.
  7. M. Schultze: A heatable object table and its use in investigations of the blood. In: Arch Mikrosc Anat. 1, 1865, pp. 1-42.
  8. V. Gazzaniga, L. Ottini: The discovery of platetets and Their function. Vesalius 7 (2001) (1), pp. 22-6