Physiology of clotting and bleeding It is fascinating that life hangs so much on the fine line our bodies play in ensuring that we neither over clot nor bleed. Most however are due to non haematological conditions and the challenge is to alter the thrombosis/bleeding balance in favour of the patient. Prevention of excessive blood loss internally and externally is key to survival. The ultimate step in clotting is the coversion of Fibrinogen to fibrin which is cross linked which helps prevent further bleeding. There are two separate pathways for activation of the cloting sytem. Both pathways converge on the reaction where Factor X is converted to factor Xa Intrinsic Requires presence of calcium ions Involves high molecular weight kininogen There is activation of Factor XII -> Factor XIIa Factor XI -> Factor XIa Factor IX -> Factor IXa Factor VIII activates Factor X -> factor Xa Measured by APTT eg detect Haemophilia or Heparin Extrinsic Requires calcium and tissue factor Factor VII -> factor VIIa + Tissue factor activated Factor X-> factor Xa
Posted on: Tue, 26 Aug 2014 05:00:01 +0000
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