Lectures L . B . 1 A modern view of haemostasis Jacek

The first model of coagulation was proposed in the 1960s. Although the cascade concept of coagulation represented a significant advance in understanding of coagulation system and served for many years as a useful model, more recent clinical and experimental observations demonstrate that the cascade/waterfall hypothesis does not fully and completely reflect the events of haemostasis in vivo. The original cascade models were subsequently modified to include new observations. It was recognized from the earliest studies of coagulation that cells were important participants in the coagulation process. Haemostasis is regulated by cellular elements. Different cells express either procoagulant (platelet, leukocytes, fibroblasts) or anticoagulant (vascular endothelium) components (proteins, phospholipids, receptors) and in this way coordinate haemostasis system. In cell-based models of coagulation (CBM) we recognize three steps: • initiation of coagulation on TF-bearing cells, • amplification of the procoagulant signal by thrombin generated on the TF-bearing cell, • propagation of thrombin generation on the platelet surface. Cell-based models of coagulation first made a conceptual leap to explain the clinical presentations of haemostatic disorders that could not be explained with classical models using intrinsic and extrinsic pathways. Actually another coagulation model system is being discussed. The clot lifespan model has been designed to complement the CBM-based approach and to elucidate the mechanisms responsible for a variety of haemostatic disorders/phenomena. The modern haemostasis models have esentially changed our view on haemostatic system. For the last years they had a significant impact on basic science and will probably have further influence on laboratory diagnostics in near future. L.B.2