First of all, we all need to know what hemostasis is. It has primary and secondary hemostasis. Primary hemostasis is forming a platelet plug, and secondary hemostasis is coagulation and resulting in activation of fibrin. Clotting factors are proteins present in the blood which control bleeding. When a blood vessel gets injured, the walls of the blood vessel contract (vasoconstriction) to slow down the flow of blood to the injured area. After that, blood cells called Platelets, also known as thrombocytes which are colourless cells, adhere to the site of injury and spread over the surface of the vessels to stop or prevent bleeding.
Alongside, the chemical signals are released from tiny sacs of the platelets, and these signals attract other cells to the damaged area and make them clump together to form platelet plugs which are primary hemostasis. The surface of the activated platelets has many different clotting factors that form a fibrin clot. The fibrin clot acts like a mesh to stop the bleeding. Normally, Coagulation factors circulate in the blood in an inactive form. When a blood vessel is injured, the coagulation cascade gets initiated—activation of coagulation factors in an order that leads to the formation of the blood clot.
The clotting factors are named after the scientists who discovered them, except for factor ix or Christmas, named after the patient.
Stages Of Blood Clotting:
Blood clotting occurs in three stages:
1. Formation of Prothrombin Activator.
2. Conversion of Prothrombin into Thrombin.
3. Conversion of Fibrinogen into Fibrin.
Process:
1. Whenever an injury occurs, the platelets (thrombocytes) move to the injured site and secrete thromboplastin, also known as tissue factor.
2. This thromboplastin (factor III) initiates the synthesis of an enzyme named thrombokinase through a series of biochemical reactions known as cascade processes. The clotting cascade involves: Intrinsic pathway and Extrinsic pathway.
Intrinsic pathway:
It begins with factor XII. If blood escapes into tissue spaces, factor XII gets activated when contact with collagen. Factor XII is a serine protease that will activate factor XI. This factor activates factor IX, which in turn activates factor X.
Extrinsic pathway:
Cells that present external to the blood vessels produce a protein called tissue factor. This factor activates factor VII, which in turn activates factor V.
1. Now the two pathways converge; the thrombokinase (factor X) converts the prothrombin into thrombin with the help of calcium ions.
2. Thrombin activates the soluble fibrinogen by converting it into insoluble fibrin.
3. Eventually, the fibrin, together with the blood cells, forms the Blood clot. (With the help of clotting Factor VIII).
The formation of a blood clot by this process is balanced by the other reactions which inhibit the clotting process, and when the blood vessel heals, the clots dissolve. Minor blood vessel injuries may trigger widespread clotting throughout the body, which happens in some diseases, revealing the significance of the control system in blood clotting.