Thrombocyte

Anatomy

They are the smallest illustrated elements of blood. The cytoplasm is very rich and one finds there:

Of the organoids: mitochondries, lysosomes, cytosquelette.
Of the granulations alpha: who contain factors of coagulation, fibrinogen and growth factors.
Of the dense granulations: they are connected to the membrane and the surface of the cell. They contain calcium, ADP (which support plate aggregation) and of the serotonin (which activates the vasoconstriction).

Physiology

Production

The Thrombopoïèse is carried out on the level of osseous marrow. It is divided into several stages, putting in turn in scene cellular divisions and differentiations.

Like any differentiated cell, the plates derive from an original cell called also totipotente. Then those are different in cells multipotentes. One then observes a differentiation in CFU-GEMM (Colony Forming Unit - Granulocyte-Erythroid-Makrophage-Megakaryocyte) which will also be able, following several differentiations, to give rise to the érythrocyte S or to the Macrophage S.

These CFU-GEMM are different then in precursors from each line, of which the CFU-MK (Colony Forming Unit - MegaKaryocytic), which will give the mégacaryoblastes. After several cellular divisions (7 on the whole), one observes in the Cytoplasme, a polyploid core. The mégacaryocyte indeed undergoes several cycles of cellular division during which he retorts his DNA. However, none being concluded its, the core doubles its quantity of DNA to each division.

These false divisions called endomitoses complete the thrombopoïèse: the mégacaryoblastes will become mégacaryocytes basophilic, then granulous and thrombocytogenes. The cell measures then from 100 to 150 micrometers and the core comprises 114 times the normal quantity of DNA: this last condenses before being eliminated by caryopinocytose.

Consequently, the proplaquettes (from 5 to 7, in the mégacaryocytes) will be released, and they even literally will explode to give birth of 1 000 until 1 500 plates each one. The plates are then released in blood, so that they can fill the fundamental role in survival of the body.

Circulation

Function

Their principal function consists in transforming the Fibrinogène (present in the Blood plasma) of fibrous structures of fibrin which, in their turn, enclose the other blood cells a such fishing net, which narrows all gently the structure of the net, thus preventing the heavy bleeding: it is thus formed a red crust sinks, which stops the wound, and which will end up being taken down at the end of the Cicatrisation. The thrombocytes are thus important for the blood coagulation.

Plates, or thrombocytes, are anucléées particles from 2 to 4 microns in diameter. After coloring with the MGG, one highlights two zones:

central: containing granulations azurophiles, called granulomère (or chromomère). One finds serotonin, ADP/ATP, calcium;
peripheral or hyalomère: fibrinogen, specific antigen of factor VIII, factor IV, fibronectine.

Their normal concentration is from 150 to 400 G/L

< 150: thrombopénie
> 400: thrombocytose

The plates are released by the thrombocytes which burst at the time of the passage in the circulatory torrent, their diameter of approximately 11 microns not allowing the passage in the vessels of spleen of a diameter of 3µm. Their main role is that of the primary hémostase which occurs when there is solution of " continuité" (paradoxically, i.e. rupture) within the vascular endothelium; in other words that the under-endothelium is exposed to the circulatory torrent (internal bleeding or external).

This phenomenon induces a vascular reaction vasoconstrictrice resulting in ' share to decrease the local speed of passage of all proteins and blood elements, and in addition to increase the local concentration of certain mediators.

After a phase of aggregation the plates can fix the under-endothelium via the factor of Von Willebrand and the fibrinogen which bridge respectively the under-endothelium with proteins IB and IIB, IIIA of the plates. The plates, from a form discoïdale at rest, pass then to a spherical form. An amplification of the phenomenon led to the formation of a white thrombus (blood clot made up of bound plates the ones with the others to which the leucocytes are acollent). It follows the constitution of a fibrin network from there in which the red globules are enchased and immobilized, it is the red thrombus.

The plates intervene in coagulation by fixing a complex prothrombinase which transforms the prothrombine into thrombin, thrombin being itself responsible for the degradation of fibrin fibrinogen.

Role in the diseases

Abnormally raised or lowered values

A normal numeration of thrombocytes at a healthy person is between 150 and 400 (X 10⁹/Liter S of blood).

In the event of disorders of coagulation one can meet as well:

a Thrombocytopenia or thrombopénie (low rate). Generally, such rates increase the risks of Hémorragie (although there are exceptions, for example the Thrombocytopénie immune induced by heparin)
a Thrombocytose (high rate) can involve a thrombosis (although it either generally when the high rate or of with a myéloproliferatif disorder).

In general, of the low rates do not require transfusions, unless the patient does not bleed or that the rate is descended below 5; they are contra-indicated in the event of will purpura thrombocytopenic thrombotic because that would worsen the coagulopathy.

Diseases

States involving a thrombocytopenia (lowered numeration)

idiopathic Thrombocytopenia

Purpura thrombocytopenic
Purpura thrombocytopenic thrombotic
Thrombocytopenia of medicamentous origin

States involving a thrombocytose (high numeration)

Thrombocytose, including the benign Thrombocytose essential

Thrombocytoses secondaries:

Splénectomie and asplénie functional
chronic acute Ignition
acute Hemorrhage
martial Deficiency
chronic Hémolyse

Thrombocytoses of the syndromes myéloprolifératifs:

the essential thrombocytose characterized by an exclusive attack of the plate line.

States involving a thrombocytopenia (lowered numeration)

haemolytic-uremic Syndrome HELLP
Syndrome

Disorders of plate adhesion or plate aggregation

Syndrome of Bernard-Shoe
Thrombasthenia of Glanzmann
Syndrome of Scott
Disease of von Willebrand

Disorders of the metabolism of thrombocytes

Hyperactivity of the Cyclo-oxygénase, induced or congenital
Storage pool defects , acquired or congenital

Transfusion

See too

External bond

the diseases concerning the plates are treated, inter alia, in the medical encyclopedia Vulgaris

Simple: Platelet

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