Platelet

Read more about this disease, some with Classification – Types – Signs and symptoms – Genetics – Pathophysiology – Diagnosis – Screening – Prevention – Treatment and management – Cures and much more, some including pictures and video when available.

Platelets, or thrombocytes, are small cytoplasmic bodies derived from cells. They circulate in the blood of mammals and are involved in hemostasis leading to the formation of blood clots. Like red blood cells, platelets have no nucleus.

If the number of platelets is too low, excessive bleeding can occur; however, if the number of platelets is too high, blood clots can form (thrombosis), which block blood vessels, and may cause a stroke and/or a heart attack. An abnormality or disease of the platelets is called a thrombocytopathy[1], which could be either a low number (thrombocytopenia), a decrease in function (thrombasthenia) or an increase in number (thrombocytosis).

The function of platelets is the maintenance of haemostasis. Primarily, this is achieved by the formation of thrombi, when damage to the endothelium of blood vessels occurs. Conversely, thrombus formation must be inhibited at times when there is no damage to the endothelium.

The inner surface of blood vessels is lined with a thin layer of endothelial cells that, in normal hemostasis, acts to inhibit platelet activation by producing endothelial-ADPase, noradrenaline, and PGI2. Endothelial-ADPase clears away ADP, a platelet activator, from platelet surface receptors.

Endothelial cells produce a protein called von Willebrand factor, a cell adhesion ligand, which helps endothelial cells adhere to collagen in the basement membrane. Under physiological conditions, collagen does not pass into the bloodstream; however vWF is secreted constitutively into the plasma by the endothelial cells that produce it, or otherwise is stored within the endothelial cell or in platelets.

When endothelial damage occurs, platelets come into contact with exposed collagen and vWF, causing a reduction in secretion of endothelium platelet inhibitors.

The inner surface of blood vessels is lined with a thin layer of endothelial cells. Under this is a layer of collagen. When the endothelial layer is injured, the collagen is exposed.

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