3) Blood Clotting/Coagulation
Thrombus = blood clot
Blood that remains in the blood vessels remains in liquid form. However, if it leaves the body it becomes a gel or clot. The process of clot formation or coagulation is a series of chemical reactions that allows for the formation of fibrin threads (a network of insoluble protein fibres which trap formed elements of the blood). Clotting factors cause fibrin to stick together and seal the inside of the vessel.
Clotting Factors including Ca++, inactive enzymes synthesized by hepatocytes, and various molecules released by damaged tissue. Clotting is a complex cascade of enzymatic reactions activating many molecules in sequence with the final product being a large quantity of Fibrin. Clotting is divided into 3 stages:
1) Two pathways: Extrinsic and Intrinsic Pathways lead to the formation of Prothrombinase.
2) Prothrombinase converts Prothrombin into the enzyme Thrombin
3) Thrombin converts soluble Fibrinogen into insoluble Fibrin – which forms the threads of the clot. The extrinsic pathway is initiated by tissue trauma. It occurs rapidly (seconds) if trauma is severe. The intrinsic pathway is initiated by blood trauma. It is a more complex process and takes longer (several minutes). Activators are in direct contact with or within the blood (outside tissue damage is not needed). Trauma to endothelial cells can initiate this pathway.
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