Sunday, October 12, 2014


 Platelets,  coagulation factors and endothelial cells lining the blood vessels are essential for adequate hemostatsis. The platelets are formed from megakaryocytes and circulate in the blood for 7-10 days. Megakaryocytes are present in the bone marrow and platelets are formed from their fragmentation.

When the endothelial lining is disrupted and underlying matrix is exposed , platelets and coagulation factors interact to plug the aberration by forming a thrombosis. The plug is formed by platelets in combinition with subendothelium von Willibrand factor and membrane glycoproteins. This is known as primary hemostatsis. Defects in platelets result in ineffective primary hemostatsis. 

In response to injury, the platelets form and initial plug on the site of injury and later on the coagulation factors support this plug with fibrin mesh.

Defects in coagulation factors result in ineffective secondary hemostatsis.

Primary hemostatic disorders result in  prolonged bleeding time, and the characteristic physical examination findings such as petechiae and purpura. In comparison, defects in secondary hemostasis result in delayed deep bleeding (eg, into muscles and joints) and the characteristic physical examination finding is hemarthrosis. 
Hemarthrosis and muscle hematomas are not present in primary hemostatic disorders.

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