Platelet
A platelet is a cell fragment that circulates in the blood. Platelets are involved in hemostasis through the making of blood clots. A low platelet count (number of platelets in the blood) can cause a person to bleed without their blood clotting (making scabs). A high platelet count can increase the risk of thrombosis (blood clots inside blood vessels), which stops blood from flowing properly.
Anatomy
Platelets do not have a cell nucleus. They are disc-shaped, and are 1.5 to 3 micrometers in diameter. The body does not have a lot of platelets, so they can all be used up quickly. They contain RNA, a canalicular system, and several different types of granules; lysosomes (containing acid hydrolases), dense bodies (containing ADP, ATP serotonin and calcium) and alpha granules (containing fibrinogen, factor V, vitronectin, thrombospondin and von Willebrand factor), the contents of which are released when the platelet is activated.
Platelet Media
- Platelet Response Animation.gif
The ligands, denoted by letter L, signal for platelets (P) to migrate towards the wound (Site A). As more platelets gather around the opening, they produce more ligands to amplify the response. The platelets congregate around the wound in order to create a cap to stop blood flow out of the tissue.
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Platelets derive from multipotent marrow stem cells.
- 1908 Platelet Development.jpg
Platelets extruded from megakaryocytes
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3D rendering of four inactivated and three activated platelets
- Red White Blood cells.jpg
Scanning electron micrograph of blood cells. From left to right: human erythrocyte, activated platelet, leukocyte.
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Diagram of the structure of a platelet showing the granules
- Platelets.jpg
Platelet clumps in a blood smear
- First and second wave of platelet aggregation.png
On for example optical densitometry, a first and second wave of platelet aggregation is seen, in this case for an ADP-initiated aggregation.
- Plateletbloodbag
Platelets collected by using apheresis at an American Red Cross donation center
