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PLATELETS
The image above shows a number of platelets stained purple associated with some RBC's.
Blood platelets, or thrombocytes, are not true cells, but rather cytoplasmic fragments of a large cell in the bone marrow, the megakaryocyte. The central portion of a platelet stains purple with Wright's stain and is referred to as the granulomere. The peripheral portion stains clear and is called the hyalomere.
Platelet contents include glycogen granules, the open canalicular system (OCS), which is composed of canaliculi formed from invaginations of the platelet plasma membrane, mitochondria, occasional Golgi elements and ribosomes. Platelets have several types of membrane-bound granules which contain a number of constituents including fibrinogen and several growth factors (e.g., PDGF).
Platelet activation occurs when injury to the vessel wall exposes sub-endothelial components, especially collagen. Platelets adhere to the damaged area and become cohesive to other platelets. This aggregation leads to the formation of a platelet plug, which prevents further blood loss and allows the repair process to begin. The micrograph shown below shows activated platelets adhering to some damaged cells.
Severe reduction in the number of circulating platelets results in a condition known as thrombocytopenia.
It is a condition which causes spontaneous bleeding as a reaction to minor trauma. This is due to failure of the platelets to seal over microscopic breaches in blood vessel walls.
In the skin this is manifest by a reddish-purple blotchy rash. This can be either small blotches called purpura or larger bruise like areas called ecchymoses.
Cytotoxic drugs used in treatment of cancers may cause this condition. It is also seen associated with acute leukaemias.
This page last updated Wednesday, 28 April 1999 20:59 +0100
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