Mechanism of blood coagulationMechanism of blood coagulationBlood Blood clotting takes place in three essential steps:clotting takes place in three essential steps:FirstFirst : : Formation of prothrombin activatorFormation of prothrombin activator

Second:Second: The prothrombin activator catalyzes the The prothrombin activator catalyzes the conversion of prothrombin into thrombinconversion of prothrombin into thrombin

Third:Third: The thrombin acts as an enzyme to convert The thrombin acts as an enzyme to convert fibrinogen into fibrin, that enmesh platelets, blood fibrinogen into fibrin, that enmesh platelets, blood

cells,& plasma to form the clot itself.cells,& plasma to form the clot itself.

Formation of prothrombin activator Trauma to the tissues, trauma to the blood , or contact of Trauma to the tissues, trauma to the blood , or contact of

the blood with damaged endothelial cells lead to the blood with damaged endothelial cells lead to formation of prothrombin activator which then causes formation of prothrombin activator which then causes

conversion of prothrombin to thrombin conversion of prothrombin to thrombin

There are There are two basic pathwaystwo basic pathways in which prothrombin in which prothrombin activator can be formed;activator can be formed;

1- 1- The extrinsic pathway;ThatThe extrinsic pathway;That begins with the trauma begins with the trauma to the vascular wall or to the tissues outside the blood to the vascular wall or to the tissues outside the blood vesselsvessels2- The 2- The intrinsic pathwayintrinsic pathway; That begins in the blood itself.; That begins in the blood itself.

The Extrinsic MechanismThe Extrinsic Mechanism12-20 Seconds12-20 Seconds• This mechanism begins when the blood This mechanism begins when the blood

come in contact with come in contact with traumatized vascular wall or extra vascular tissue, the traumatized vascular wall release two factors;;

• Tissue factor which is the protolytic Tissue factor which is the protolytic enzyme enzyme

Tissue phosholipid which are mainly Tissue phosholipid which are mainly phosholipid of the tissue cell phosholipid of the tissue cell memberane.memberane.

Mechanism of blood coagulationBlood clotting takes place in three essential steps::

• 1-Formation of prothrombin activator.• 2-The prothrombin activator catalyze conversion of

prothrombin into thrombin• 3-The thrombin acts as enzyme to convert

fiberinogens into fiberin threads that enmesh threads that enmesh platelets,blood cells and plasma to form the clot itself.platelets,blood cells and plasma to form the clot itself.

• 1- Formation of prothrombin activator;• Trauma to the tissues, trauma to the blood or contact of the Trauma to the tissues, trauma to the blood or contact of the

blood with damaged endothelial cells lead to formation of blood with damaged endothelial cells lead to formation of prothrombin activatorprothrombin activator

• There are two basic pathways: There are two basic pathways: • 1- 1- The extrinsic pathway; that begins with the ; that begins with the

trauma to the vascular wall or to the tissues outside the blood trauma to the vascular wall or to the tissues outside the blood vessels.vessels.

• 2- The intrinsic pathway; That begins in the blood That begins in the blood itselfitself

•The extrinsic mechanismThe extrinsic mechanism

• This mechanism begins with blood come in contact This mechanism begins with blood come in contact with traumatized vascular wall or extra vascular with traumatized vascular wall or extra vascular tissues tissues

• The traumatized vascular wall release two factors;;

• 1- Tissue factor,: which is photolytic enzyme. which is photolytic enzyme.• 2- Tissue phospholipids,: which are ,: which are

phospholipids of the tissue cell membranes.phospholipids of the tissue cell membranes.• II- II- Activation of factorΧ ; the tissue factor ; the tissue factor

complex with factor VII ,in the presence of calcium complex with factor VII ,in the presence of calcium acts enzymatically on factor X To form activated acts enzymatically on factor X To form activated factor X factor X

• III- formation of prothrombin activator• The activated factor X complex with tissue The activated factor X complex with tissue

phospholipids and with factor V to form phospholipids and with factor V to form prothrombin activator.withen few second the prothrombin activator.withen few second the prothrombin activator splits prothrombin to form prothrombin activator splits prothrombin to form thrombin thrombin

• The intrinsic mechanismThe intrinsic mechanism• This mechanism begins with the This mechanism begins with the trauma

inside the blood vessels• Factor XII is activated when coming in is activated when coming in

contact with collagen fiberscontact with collagen fibers• Activated factor XII then activates factor XI then activates factor XI• Activated factor XI then activate factor IX then activate factor IX• Activated factor IX in the presence of in the presence of

factor VIII and with platelets phospholipids factor VIII and with platelets phospholipids activates factor Xactivates factor X

• Activated factor X in the presence of factor in the presence of factor V ,calcium ions and platelets phospholipids V ,calcium ions and platelets phospholipids for a complex called prothrombin activatorfor a complex called prothrombin activator . .