 Hello everyone, welcome back to another session in dentistry and more. So today we have hemostasis in human physiology. So hemostasis is the mechanism of blood coagulation. So this video is all about the three steps of hemostasis that is the vasoconstriction, platelet, blood formation and blood coagulation and the blood coagulation in detail the intrinsic and extrinsic pathway. So let's learn about hemostasis and blood coagulation. So hemostasis, hemostasis it is defined as arrest or stoppage of bleeding and the stages of hemostasis. So what happens when a blood vessel is injured, the injury initiates a series of reactions which results in hemostasis which occurs in three stages. The first stage is vasoconstriction where the construction of vessels happens. Then the second stage is platelet, platelet formation there will be accumulation of platelets and there will be a temporary platelet formation and finally the coagulation of blood. So the first step, vasoconstriction. So in vasoconstriction, so immediately after the injury, the blood vessel constricts and decreases the loss of blood from damaged portion. So these blood vessels are cut and the enterothelium is damaged and there will be exposure of the collagen fibers. So what happens is when the damage happens platelet comes to action and they adhere to this collagen and gets activated. So these activated platelets secrete serotonin and other vasoconstrictive substances which cause constriction of blood vessel. So this attachment of platelets to the collagen is accelerated by one will brand factor. So you must have heard of that factor, one will brand factor and this factor acts as a bridge between a specific glycoprotein present on the surface of platelet and collagen fibrils. So this is acting as a bridge between the platelets and collagen fibrils. So in platelet plague formation, once the platelet get adhered to the collagen ruptured blood vessels, there will be secretion of adenosine life phosphate and also thromboxin A. So these two substances attract more and more platelets and activate them. So all these platelet aggregates together and form a loose temporary platelet plague. So there will be a platelet plague formation because this will attract more and more platelets which close the ruptured vessel and prevent further blood loss. So these platelet aggregation is accelerated by platelet activating factor that is P-A-F platelet activating factor. So that is platelet plague formation the second stage whereas the third stage that is a coagulation of blood. So during this process the fibrin origin is converted into fibrin. So that is what we are going to learn. So fibrin threads get attached to the loose platelet plug which plexure ruptured part of blood vessel and prevents further blood loss completely and by definition blood coagulation or blood clotting is defined as process in which blood loses its fluid and becomes a jelly like mass few minutes after it is shut out that is coagulation. So it loses its fluid and it becomes a jelly like mass after a few minutes. That is blood coagulation or blood clotting. So before learning the two pathway that is intrinsic and extrinsic pathway we need to learn the clotting factors. So coagulation of blood which occurs through a series of reactions due to the activation of group of substances which is necessary for clotting. These are known as clotting factors. So we have 13 clotting factors. The factor number one is fibrin origin, two is prothombin, three is thromboplastin or also known as tissue factor and the fourth one is calcium, fifth one is labial factor, sixth one is not yet proved, there is no component mentioned as six, whereas the seventh one is stable factor, eighth one is anti-hemophilic factor, ninth one is Christmas factor, tenth one is Stewart-Prowler factor, eleventh is plasma thromboplastin antecedent or PTA, 12th one is Higman factor or contact factor, 13th is fibrin stabilizing factor. So these are the 13 clotting factors which involve in the clotting mechanism either in intrinsic pathway or extrinsic pathway. So sequence of clotting mechanism. So most of the clotting factors are proteins in the form of enzymes. So normally all factors are present in the form of inactive pro-enzyme, that is not able to activate any, so pro-enzyme is not able to conduct any such reactions. So these pro-enzyme must be activated into enzymes to enforce clot formation. So it is carried out by a series of pro-enzyme enzyme conversion and first one of the series is converted into active enzyme, that activates the second one then which activates the third one and this continues till the final active enzyme thrombin is formed. So till here there will be continuous activation, 12th becoming active that in turn is making active of 11th factor, 9th factor, 10th factor. So we have basically three steps of blood clotting that is three stages that is formation of pro-thrombin activator from injury to here. The second stage is conversion of pro-thrombin into thrombin and the third step is conversion of fibrin origin into fibrin, so stage one, stage two and stage three. So stage one is formation of pro-thrombin activator. So from the damage to pro-thrombin activation is within stage one that is blood clotting commences with the formation of substance called pro-thrombin activator which converts to pro-thrombin and thrombin. Its formation is initiated by substances either within the blood or outside the blood. This is the formation of pro-thrombin activator occurs through two pathways. So within the blood is intrinsic pathway and outside the blood is extrinsic pathway. This is within, this is outside, that is why it is known as extrinsic and this is intrinsic. So that is pro-thrombin activator which converts pro-thrombin to thrombin. So intrinsic pathway mechanism, so this is intrinsic pathway. So what happens is, so in this pathway the formation of pro-thrombin activator is initiated by platelets which are within the blood itself. These platelets are present within the blood. So in intrinsic pathway what is happening? So during the injury the blood vessel is ruptured, endothelium is damaged and collagen beneath the endothelium is exposed. So this is a twelfth factor which is known as Hegman factor. This twelfth factor which comes in contact with this collagen and it is converted into a activated, so this A means activated. So activated factor 12 in the presence of chelicrine. So in the presence of chelicrine this twelfth factor become activated. So this activated twelfth factor, in turn activate the inactive eleventh factor. This is a series of reactions. So the eleventh factor become activated. So the eleventh factor is in turn activating the ninth factor. The ninth factor is Christmas factor, eleventh factor is plasma thromboplastin antecedent. So ninth factor is getting activated with the help of eleventh factor and the ninth activated factor changing the tenth factor into tenth activated factor that is toward provo factor. So twelfth, eleventh, ninth and tenth that is a sequence, okay, twelfth, eleventh, ninth and tenth. This is not happening in a decreasing order like twelfth, eleventh and tenth, it is happening twelfth, eleventh, ninth and tenth. So thereby prothrombin activator forms via platelets and formation of phospholipids and prothrombin activator which activates prothrombin to thrombin, okay. So that is happening in the stage two. So prothrombin is converted to thrombin, okay. So there will be two mechanism that is positive feedback mechanism and negative feedback mechanism with thrombin and prothrombin activator, okay. So once the thrombin forms that is coming under stage two. So there will be two mechanisms whereby thrombin formation is activated by prothrombin activator that is either positive feedback or negative feedback. When there is increased demand of thrombin the positive feedback mechanism will work and there will be amplification of thrombin production and if the thrombin production is not very much is required then there will be negative feedback mechanism happens and the production will decrease that is a second mechanism that is negative feedback, okay. So after that this thrombin fibrinogen will be converted to with the help of thrombin fibrinogen will be converted to fibrinogen A then there will be loose transfer of fibrin and ultimately a fibrin tight blood clot is formed. So that is blood clot formation or blood coagulation, okay. So whereas the extrinsic pathway what happens is the formation of prothrombin activator is initiated by the tissue thromboplastin which is formed from the insured tissue, okay that is tissue thromboplastin this is a mixture of glycoprotein and phospholipid. So tissue thromboplastin is formed from the insured tissue and this tissue trauma which activates the factor number 10 with the help of factor number 7 and this activated factor 10 is helping the prothrombin activator with the help of calcium and factor number 5, okay and the same mechanism will happen positive and negative feedback and it will go to stage 3 either intrinsic or extrinsic pathway that is conversion of thrombin, thrombin will convert fibrinogen to fibrinogen A then there will be loose transfer of fibrin and ultimately fibrin tight blood clot happens, okay. So that is the mechanism of blood clotting or blood coagulation it is happening in three stages basically that is vasoconstriction, platelet plaque and blood coagulation. So the blood coagulation again happening in three stages stage 1, stage 2 and stage 3 stage 1 is until the prothrombin activator formation stage 2 is thrombin formation and stage 3 ultimately the blood clot forms and it could happen two ways intrinsic and extrinsic pathway intrinsic the factors involved are factor number 12, 11, 9, 10 and prothrombin activator converts prothrombin to thrombin whereas extrinsic pathway is thromboplastin which converts 10 factor with the presence of 7 and the activated factor number 10 is helping prothrombin activation to convert prothrombin to thrombin with the help of calcium and factor number 5 and finally the thrombin converts fibrinogen to fibrinogen A and fibrin to ultimate fibrin tight blood clot, okay. So this could be long assay like intrinsic pathway or extrinsic pathway or the mechanism of blood coagulation or hemostasis as a long assay and the clotting factors 13 clotting factors such as fibrinogen, prothrombin, thromboplastin which is also known as tissue factor, calcium labial factor then 7 is stable factor, 8 is anti hemophilic, Christmas factor, Stuart pro factor, plasma thromboplastin, anticitin, 12 is hegen factor and 13 is fibrin stabilizing factor. So that's all about blood coagulation, hemostasis or blood clotting or intrinsic and extrinsic pathway. So I'll come up with a new topic in physiology, thank you.