Chapter 24: Platelets, Blood Coagulation and Haemostasis

Platelets, Blood Coagulation and Haemostasis details the life cycle and structural complexity of platelets, which originate from marrow megakaryocytes under the regulation of thrombopoietin and the Ashwell-Morell receptor. The text delves into the biochemical architecture of platelets, highlighting the critical roles of surface glycoproteins like Ib and IIb/IIIa in adhesion to von Willebrand factor and collagen, as well as the significance of internal alpha and dense granules in the release and amplification phases. A substantial portion of the discussion is dedicated to the coagulation cascade, tracing the journey from the initial exposure of tissue factor and the activation of Factor VII to the explosive generation of thrombin. This enzymatic burst facilitates the conversion of soluble fibrinogen into a stable fibrin meshwork, reinforced by Factor XIII. The chapter also emphasizes the regulatory mechanisms that prevent pathological thrombosis, including natural inhibitors such as antithrombin and the protein C and S system, alongside the fibrinolytic pathway where plasmin dissolves established clots. Finally, it outlines essential laboratory diagnostics, explaining how screening tests like the prothrombin time (PT), activated partial thromboplastin time (APTT), and thrombin time (TT) help clinicians identify specific factor deficiencies or platelet dysfunction, ensuring a comprehensive understanding of both normal physiology and haematological disorders.