Blood coagulation
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Blood coagulation, or clotting, is a crucial process that prevents excessive bleeding when blood vessels are injured, involving platelets and plasma proteins. Hemostasis consists of three main steps: vasoconstriction, platelet plug formation, and blood coagulation, leading to wound healing. Key components such as platelet activation and clotting factors facilitate the transition from liquid blood to a solid clot, which helps seal the injury until tissue repair occurs.
Blood coagulation
- 1. Blood coagulation Anup Muni Bajracharya
- 2. Blood clotting • Blood clotting, or coagulation, is an important process that prevents excessive bleeding when a blood vessel is injured. • Platelets (a type of blood cell) and proteins in our plasma (the liquid part of blood) work together to stop the bleeding by forming a clot over the injury. • Hemostasis or haemostasis is a process which causes bleeding to stop, meaning to keep blood within a damaged blood vessel (the opposite of hemostasis is hemorrhage). • It is the first stage of wound healing. This involves coagulation, blood changing from a liquid to a gel.
- 3. Steps in Hemostasis • Hemostasis has three major steps: • 1) vasoconstriction/ Vascular spasm • 2) temporary blockage of a break by a platelet plug, and • 3) blood coagulation, or formation of a fibrin clot. These processes seal the hole until tissues are repaired. Basic events in blood clotting: The basic events of the process of blood clotting or coagulation can be stated as follows Vascular injury -------> vascular spasm------>Platelet plug formation ------>blood coagulation.
- 4. Terminology • Vascular injury: It refers to the injury of the blood vessel leading to the disruption of the capillary endothelium that causes loos of blood.. • Vascular spasm: It refers to the contraction of the smooth muscle fibers of the all of the blood vessel (not a capillary essentially) that reduced the flow of blood to the damaged section of the vessel. Signals from nocireceptors initiate the process. • Platelet plug formation: It refers to the action of the platelets to form a plug at the site of injury involving platelet adhesion, platelet release reaction where different substances like prostaglandins, serotonin, ADP etc. are released from platelets. This results in formation of a platelet plug along with fibrin and some WBC and a few stranded RBC. • Blood coagulation :The aforestated processes cause the coagulation of blood or blood clotting with blood clotting factors.
- 5. Vascular spasm (Vasoconstriction) • When a blood vessel is damaged, there is an immediate reflex, initiated by local sympathetic pain receptors, which helps promote vasoconstriction. • The damaged vessels will constrict (vasoconstriction) which reduces the amount of blood flow through the area and limits the amount of blood loss.
- 6. Contd… • Collagen is exposed at the site of injury, the collagen promotes platelets to adhere to the injury site. • Platelets release cytoplasmic granules which contain serotonin, ADP and thromboxane A2, all of which increase the effect of vasoconstriction.
- 7. Platelet plug formation • Platelets adhere to damaged endothelium to form a platelet plug (primary hemostasis) and then degranulate. • Plug formation is activated by a glycoprotein called Von Willibrand factor (vWF), which is found in plasma. • When platelets come across the injured endothelium cells, they change shape, release granules and ultimately become ‘sticky’. • Platelets express certain receptors, some of which are used for the adhesion of platelets to collagen.
- 8. • When platelets are activated, they express glycoprotein receptors that interact with other platelets, producing aggregation and adhesion. • Platelets release cytoplasmic granules such as adenosine diphosphate (ADP), serotonin and thr omboxane A2. • Adenosine diphosphate (ADP) attracts more platelets to the affected area, serotonin is a vasoconstrictor and thromboxane A2 assists in platelet aggregation, vasoconstriction and degranulation.
- 9. Clot formation • Once the platelet plug has been formed by the platelets, the clotting factors (a dozen proteins that travel along the blood plasma in an inactive state) are activated in a sequence of events known as 'coagulation cascade' which leads to the formation of fibrin from inactive fibrinogen plasma protein. • Thus, a fibrin mesh is produced all around the platelet plug to hold it in place; this step is called "Secondary Hemostasis". • During this process some red and white blood cells are trapped in the mesh which causes the primary hemostasis plug to become harder: the resultant plug is called as 'thrombus' or 'Clot'.
- 10. Blood clotting factors Clotting involves several chemicals known as as blood clotting factors. A few platelet coagulation factors are released by platelets. Thromboplastin or tissue factor is found on surface of various body cells.
- 11. Blood clotting factors Coagulation factor synonym I Fibrinogen II prothrombin III Tissue factor (Thromboplastin) IV Calcium ions V proaccelerin / labile factor / accelerator globulin VII Serum prothrombin conversion accelerator(SPCA) / stable factor / proconvertin VIII Antihaemophilic factor(AHF) IX Christmas factor / plasma thromboplastin component ( PTC)/ AHF B X Stuart factor / Power factor / thrombokinase XI Plasma thromboplastin antecedent(PTA) / AHFC XII Hageman factor ? Glass factor/ contact factor XIII Fibrib stabilizing factor (FSF) / Fibrinase
- 12. Stages of biochemical pathway of blood clotting • Stage 1. Formation of prothrombin activator • Stage 2. Conversion of protthrombin into thrombin by prothrombin activator • Stage 3. Conversion of soluble fibrinogen into insoluble fibrin by thrombin. • The formation of prothrombin activator is initiated by the interplay of of two mechanisms - the Extrinsic(tissue factor) pathway that is extravascular and the Intrinsic (Contact) pathway, which is intravascular. • In both the process of initiation of prothrombin activator is different but the basic role of blood clotting factors is unchanged.