Mechanism of Blood Coagulation

When there is an injury in a blood vessel-like cut on the surface of the skin or trauma on any muscle tends to get damaged and then starts bleeding. This mechanism protects the blood vessels from further damage and repairs them. The mechanism of blood coagulation starts when there is a trigger from the damaged blood vessel.

What is blood coagulation? 

Blood Coagulation is the mechanism by which the blood turns into a gel-like substance to stop further bleeding and repairs the blood vessel. This mechanism of blood coagulation leads to hemostasis that stops blood loss and repairs the blood vessel.

Platelet Activation

The underlying isolated collagen is exposed to the circulating platelets. This collagen binds collagen with collagen-specific glycoprotein la/lla surface receptors. The von Willebrand Factor (vWF) released from the endothelium and platelet strengthens the connection between collagen and collagen-specific glycoprotein. The vWG produced forms a different link between the platelets glycoprotein lb/lX/V and A1 domain. The activation of Platelet integrins is a trigger caused by the binding of collagen to glycoprotein VI. These activated platelet integrins produce tight binding of platelets. This process initiates the movement of platelets towards the site of injury.

Mechanism of Blood Coagulation 

The mechanism of blood coagulation is based on Haemostasis. This process includes three steps: Formation of prothrombin activator, conversion of prothrombin to thrombin, conversion of fibrinogen into fibrin. Here is a small mechanism of blood coagulation notes below:

Intrinsic Pathway

This process is part of a longer pathway of secondary hemostasis. This process begins when inactivated Factor XII transforms into activated Factor XIIA after it gets exposed to endothelial collagen. The exposure of endothelial collagen occurs only when there is endothelial damage. In this whole process of activating factor XI to Factor XIA, Factor XII acts as a catalyst.

Then Factor IXA gets activated from Factor IX by Factor XIA. This process is known as a cascade. After all these factors get activated, these factors go on to activate more factors in a cascade. Going down the cascade increases the concentration of that factor in the blood.  This process is the intrinsic pathway, and this is clinically measured as the thromboplastin time (PTT).

Extrinsic Pathway

This process is the extrinsic pathway. This extrinsic pathway is part of a shorter pathway of secondary hemostasis. After there is damage in the blood vessel, tissue factors are released which in turn activates factor VII to factor VIIa, by endothelial cells. This factor VIIa further activates factor X into factor Xa. Here in this point both extrinsic and intrinsic pathways merge and become one.  This extrinsic pathway is measured clinically as the prothrombin time (PT).

Common Pathway 

In the previous pathway when Factor X gets activated to Xa, this pathway starts exactly at this point. The whole process of X getting activated into Xa is caused by a complex chemical reaction. Here tenase has two forms: extrinsic (consisting of factor VII, factor III, and Ca2+) and intrinsic (consisting of cofactor factor VIII, factor IXA, phospholipid, and CA2+). Once X is activated to XA, it further activates factor II (prothrombin) into factor IIa (thrombin). 

This factor Xaneeds factor V as a cofactor to cleave prothrombin into thrombin. Then Factor IIa goes to activate fibrinogen to fibrin. The intrinsic pathway (factor XI/ as well as cofactors V and VIII and factor XIII is activated by thrombin. And fibrin strands are formed by subunits of fibrin coming together. At the same time, Factor XIII acts on fibrin strands to transform into a fibrin mesh-like structure. This fibrin mesh helps to stabilise the platelet plug.

The organ involved in the mechanism of Blood Coagulation.

The most important organ which is involved in the process of blood coagulation is the liver. It is the liver responsible for the formation of factors I, II, V, VII, VIII, IX, X, XI, XII, and protein C, and S.

Blood Clotting Disorders

The most common type of blood clotting disorder is haemophilia. It is a hereditary disorder. Other blood clotting disorders include Deep Vein Thrombosis, Pulmonary Embolism, Arterial Thrombosis, Thrombophilia, etc.

Conclusion

The mechanism of blood coagulation is an important defence mechanism of the body. It can save lives but sometimes kill a person if there is hypercoagulation in a person. The liver is the main organ behind this mechanism of blood coagulation thus one should keep in mind that, the liver should be taken care of to keep this mechanism in an equilibrium state so that it does not cause harm to the body.