Primary hemostasis
In the case of an injury the tissue lining of the blood vessel (endothelium) is damaged and the subendothelial matrix (consisting of proteins such as collagen and fibronectin) is exposed. This initiates the process of platelet attaching to the subendothelial matrix. The activation of platelets takes place, and this, in turn, attracts more platelets to that area of the blood vessel. This activation process of platelets leads to the local secretion of the contents of their granules such as Adenosine diphosphate (ADP) and Ca2+.
Secondary hemostasis
The second stage of hemostasis, or simply known as coagulation, is the process of a stable protein (fibrin) clot is formed from the soluble precursor protein fibrinogen. The series of biochemical cascade of fibrin formation is classically differentiated into three pathways: intrinsic, extrinsic and common pathway. These three pathways consists of a series of enzyme activation steps ultimately leading to thrombin generation and fibrin formation. The three pathways differ by the types of cells involved (platelets, endothelial cells, fibroblasts and leukocytes) and the types of proteins (clotting factors) involved.