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© Dirk Biddle
Thrombocytes (platelets) play an active role in vascular inflammation and are important in blood coagulation and the repair of small breaches in vessel walls. Platelets are small, colourless, irregularly shaped cells that contain no nucleus or haemoglobin and normally number between 150 to 400 thousand per cubic millimetre of blood. Their cytoplasmic granules contain (among other molecules) lysosomal enzymes, adenosine diphosphate (a potent platelet aggregating factor), serotonin (a vasoactive amine) and platelet-derived growth factor (which contributes to repair processes by stimulating fibroblast proliferation). During the clotting process, platelets clump together to plug small holes in damaged blood vessels. Platelets also activate factor VIII (a clotting agent) and release phospholipids as part of the blood clotting process. The circulating life of a platelet is 9-10 days. After this it is sequestered in the spleen. Platelets however also contribute to vascular damage. Activated platelets release various pro-inflammatory mediators that generate complement activation thus augmenting neutrophil mediated vascular injury. A description of exactly how this occurs can be found in later sections.
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Lysosome: A saclike cellular organelle that contains various hydrolytic enzymes. (M+)
Adenosine Diphosphate: ADP is a nucleotide C10H15N5O10P2 composed of adenosine and two phosphate groups that is formed in living cells as an intermediate between ATP and AMP and that is reversibly converted to ATP for the storing of energy by the addition of a high-energy phosphate group. (M+)
Platelet: A particle found in the bloodstream that binds to fibrinogen at the site of a wound to begin the blood clotting process. Platelets are formed in bone marrow, where they arise from cells called megakaryocytes. (OMD)
Amine: Any of a class of organic compounds derived from ammonia by replacement of one, two, or three hydrogen atoms with alkyl groups. (M+) (organic hydrocarbon radicals)
The amines are distinguished as primary, secondary and tertiary, according to whether one, two or three hydrogen atoms are replaced. The amines include allylamine, amylamine, ethylamine, methylamine, phenylamine, propylamine and many other compounds. (OMD)
Platelet-Derived Growth Factor: The major mitogen in serum for growth in culture of cells of connective tissue origin. It consists of 2 different but homologous polypeptides A and B (~30,000 D) linked by disulphide bonds. Believed to play a role in wound healing.
Phospholipid: The major structural lipid of most cellular membranes (except the chloroplast which has galactolipids). Contain phosphate, usually as a diester. (OMD)
Any of numerous lipids (as lecithins and phosphatidylethanolamines) in which phosphoric acid as well as a fatty acid is esterified to glycerol and which are found in all living cells and in the bilayers of cell membranes. (M+)
Mediators: An object or substance (such as an enzyme, hormone or a neuropeptide) by which some (chemical or biological) process is mediated. An intermediate agency, the third agent that connects, or also as in catalyst.
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