Blood Platelets Definition

What are platelets ?

Platelets or thrombocytes are the smallest cells (2-3 microns in size) in the blood. They do not have a cell nucleus. Platelets play an important role in the prevention of bleeding (haemostasis).


Platelets are, like other blood cells formed in the bone marrow. Thrombopoietin, a hormone, stimulates the development and proliferation of giant cells called megakaryoblasten. These giant cells undergo endomitose. That is to say, that the nucleus of the cell divides, while the cell will not be herewith larger. The megakaryoblasten differentiate into megakaryocytes. These cells have a well-developed Golgi apparatus, many mitochondria, rough endoplasmic reticulum and lysosomes. By afsnoeringen of the megakaryocyte platelets are formed. From a megakaryocyte can still be formed thousands of platelets. Platelets are actually no more whole cells but only fragments. The life time of a blood platelet in the blood stream is about 8 to 10 days. The degradation of blood platelets takes place in the spleen, liver and lungs.

When a blood vessel wall is damaged, platelets to the damaged wall from sticking. This is due to the binding of platelets to collagen fibers which have been exposed by the lesion to be located. In addition, the platelets stick to each other also, aggregate, and there begins to form a clot. Also, fibrin is formed from fibrinogen. Fibrin is a fibrous substance which will form a network of threads in order to strengthen the blood clot. It also comes thromboplastin released from the damaged tissue. The released thromboplastin and the sticking of the platelets are at the beginning of a complex chain of reactions, blood coagulation, which ends with the formation of a blood clot. There may be an occlusive thrombus are formed as shown.

 or thrombocytes are the smallest cells  Blood Platelets Definition


To investigate whether someone too little, enough or has too many platelets in the blood, in a clinical chemistry laboratory in the hospital or in a GP laboratory platelet count is determined. This is usually done with a so-called hemocytometry device. This device can by means of an impedance or an optical measurement to determine what is the concentration of platelets in a person's blood. Sometimes, however, the blood platelets will clump in the tube in which the blood has decreased. This is called EDTA pseudothrombocytopenia. It is harmless for the patient (this clumping occurs only in the tube), but the number of platelets is then no longer be determined accurately. In patients with this phenomenon than blood into a tube containing citrate conducted in order to determine the number of thrombocytes (platelets). In general, the anti-coagulant in this tube has no effect on the clotting of the platelets after the decrease.

In addition to deviations in the number of platelets can be in the clinical chemical laboratory also be done research on the ability of the platelets to aggregate, to clump together. This test is called platelet-platelet aggregation either research study. Are various substances added to the blood platelets of healthy subjects which show platelets clump together. With this research, abnormalities in the functioning of platelets are detected.


Thrombocytopenia: a shortage of platelets in the blood. The result is that bleeding due to damage of the vessel wall can not be staunched well, which can be fatal in severe cases. Also you bruise more easily.
Thrombocytosis: an excess of platelets in the blood. This spontaneous blood clots can form (thrombosis).
Thrombocytopathy: platelets have a disturbed function and do not know what they should do. The symptoms are similar to thrombocytopenia.


A shortage of platelets and risk of bleeding, it can sometimes be necessary to give a platelet transfusion. A shortage of platelets is then completed by the patient administering an trombcytenconcentraat obtained from donors. Because the supply of platelets is low, and the life of transfused platelet only a few days, this only makes sense if there is the prospect that trombocytentekort of limited duration. It is e.g. not done by people who, for whatever reason, no longer have functioning marrow and that not going to get.

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