 Hemostatic process consists of three main responses. One is vasoponstriction and platelet plug formation and finally clot formation. The formation of fibrin meshwork occurs in multiple steps. It requires initiation of the response so there will be some stimulus which will activate the process then amplification of the response. So the intensity of the response will increase and finally it leads to thrombin formation. Now thrombin is the main protein which will convert fibrinogen to fibrin. And finally there should be stoppage of this clotting process otherwise it can continue without an end to the process and a large clot will form which will be harmful also. So the steps for this fibrin clot formation occurs via two different processes. Now each process requires activation of certain proteins which will in turn activate other proteins then activate other proteins and finally which leads to thrombin formation. So this activation occurs via two different pathways. So there is intrinsic pathway and extrinsic pathway. Now extrinsic pathway is the primary pathway which is also known as primary pathway and intrinsic pathway is the secondary pathway because it is the extrinsic pathway which is the first to be activated. So what happens in extrinsic pathway that there is a protein factor 7 right which gets activated to 7A here A denotes it's activated form. So initially all the factors are kept in inactivated form obviously it is needed otherwise these clotting mechanisms will be activated even when they are not needed. So some stimulus should be there which causes their activation. So in this case the stimulus is the tissue thromboplastic along with blood vessels there is injury to tissues also and also even blood vessel injury underlying tissues will release this tissue thromboplastic which will cause activation of factor 7 to 7A. Now this factor in turn converts another factor to its activated form that is factor 10A. Now this factor in presence of 5A phospholipids and calcium it leads to formation of thrombin that is nothing but thromb factor 2 that is pro-thrombin it leads to formation of 2A that is thrombin. Now this phospholipids is provided by the surface of the platelets so the membrane of the platelet has phospholipids and on these membrane this activated mechanism takes place. So this is nothing but thrombin this thrombin in turn leads to formation of fibrin from fibrinogen. Now this fibrin is in a monomeric form that means there are single units of this fibrin so it is in monomeric form and as more and more fibrin forms there is covalent linkages forming between these fibrin monomers which leads to formation of a meshwork and these bonds are further stabilized by another protein another factor factor 13. Factor 13 is important for stabilization of these bonds between the fibrin monomers it is this stabilization which ultimately forms a fibrin meshwork. Now here we have discussed only one pathway where factor 7, factor 10, 5, 2 and fibrin is involved now this fibrinogen is nothing but factor 1 but there is another pathway known as intrinsic or secondary pathway in which other factors are involved factor 12. Obviously all the factors are getting activated so activated factor 12 leads to activation of factor 11 leading to formation of activated 11 then you know 10th is here here there is 9 this is the one which leads to activation of factor 2 10 to 10 8 so 12 11 10 9 instead of it is 12 11 9 10 just to remember how these factors are there this is not the sequence instead 9 and 10 are reversed factor 9 operates in combination with factor 8 so these are working together so we are seeing that at level of factor 10 these pathways have converged so the pathway from factor 10 to further is known as common pathway because it is common to both intrinsic and extrinsic pathways this is extrinsic pathway and this intrinsic and this extrinsic one more characteristic of this coagulation path which you should know is that this is a self-sustaining process that once initiated it will sustain itself and that is because of a positive feedback mechanism which is operating and this is brought by thrombin once generated thrombin activates many other plotting factors and these plotting factors are 5 7 9 11 and 13 so these are odd number plotting factors but instead of 9 actually it is 8 so 5 7 8 11 13 so all these steps are further being increased by thrombin so there is a positive feedback going on let's activate this one two diagram has become kind of a mess but if you would have followed it a step by step i'm sure you would have caught it so then 11 8