The coagulation system of the human body is composed of cellular elements, platelets, and series of proteins. The platelets are derived from larger cells of the bone marrow, called megakaryocytes. Primary hemostasis occurs when a platelet plug, or clump of platelets, forms at the site of an injury. This rapidly occurs and prevents blood loss from very small vessels, such as capillaries, arterioles and venules. Secondary hemostasis, on the other hand, takes several minutes to occur. It results from interactions of various clotting factors within the blood stream. This form of hemostasis, secondary hemostasis, is important for the control of bleeding from larger blood vessels. Shortly after an injury, the platelets adhere to the damaged tissue. This response of platelets causes them to release granules with them. This is one of the factors that is important in initiating and propagating secondary hemostasis. Insufficient numbers of platelets can lead to excessive bleeding by not being available in sufficient amounts to produce this reaction. Also, the platelets may become damaged or dysfunctional for a variety of reasons.
Causes of Platelet Dysfunction
There are three main groups that constitute disorders of the platelets. They include disorders of adhesion of the platelets, disorders of aggregation of the platelets and disorders of release of the granules within the platelets. Each of these types of disorders can come from inherited conditions as well as acquired conditions. Irrespective of their etiology, all of these forms of platelet disorders lead to impairment of primary and secondary hemostasis.
Signs and Symptoms of Platelet Dysfunction
Platelet disorders all interfere with primary and secondary hemostasis, or blood-clotting. Consequently, there is usually a history of excessive or easy bruising. In women, there may be excessive menstrual bleeding or frequent menstrual bleeding. Surgical procedures or injuries are often accompanied by unexpected heavy blood loss. In disorders where the platelets are isolated by the spleen, a mass may develop in the left upper abdomen. Sometimes, platelet disorders can occur in combination with viral infections, such as infectious mononucleosis, toxoplasmosis, viral hepatitis or HIV/AIDS. The symptoms that occur are then usually part of the disease process of these individual clinical entities.
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Medical Content Last Updated on 07/12/2008
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