Page 343 - Essential Haematology

Chapter 24 Platelets, blood coagulation and haemostasis / 329

■ Normal haemostasis requires ■ Blood coagulation commences with tissue

vasoconstriction, platelet aggregation and factor binding to clotting factor VII and this
blood coagulation. The intact endothelial initiates a cascade which results in
cell normally separates collagen and other thrombin generation. Thrombin then SUMMARY
subendothelial connective tissues that activates factors VIII and V which greatly
would stimulate platelet aggregation from amplify the coagulation pathway resulting
circulating blood. The endothelial cells also in a fi brin clot.

produce prostacyclin, nitric oxide and an ■ Coagulation factor inhibitors include
ectonucleotidase which inhibit platelet antithrombin, protein C and protein S.

aggregation. ■ Dissolution of fi brin clots (fi brinolysis)

■ Platelets are produced from occurs by activation of plasminogen to

megakaryocytes in the bone marrow. They plasmin.

have surface glycoproteins which facilitate ■ Tests of haemostatic function include the
adherence via von Willebrand factor to thrombin time (TT), prothrombin time (PT),
collagen, to other platelets (aggregation) activated partial thromboplastin time
and to coagulation proteins. Platelets (APTT) as well as individual coagulation
contain different types of storage factor assays and assay of von Willebrand
granules which are released after platelet factor. Tests of platelet function include the
activation. PFA - 100 and platelet aggregation test.

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