Module D4 Flashcards
3 major components of the plasma component of hemostasis
Coagulation
Natural anticoagulants and inhibitors
Fibrinolysis
Coagulation
Sequence of reactions involving the coagulation factors which result in the formation of fibrin
Function: convert the secondary platelet plug (white) into a cohesive mass that is anchored to the vessel walls by the deposition of fibrin into the white plug. Converts white to red plug, and then the hemostatic plug
Natural anticoagulants and inhibitors
When vascular damage occurs, the hemostatic mechanism is activated
Hemostasis must be limited to and localized at the site of injury
Function: regulate hemostasis by limiting clot formation
Fibrinolysis
Mechanism by which fibrin are hydrolyzed
Function: regulate the hemostatic mechanism by limiting clot formation and removal of the hemostatic plug as healing occurs
Coagulation reactions result in
Transformation of the substrate, factor 1, fibrinogen to the end product, fibrin
Cascade sequence, cascade or clotting cascade
Cascade sequence consists of 2 separate pathways
Intrinsic and extrinsic
Common
Intrinsic pathway
Activated by factor XII and or factor XI contracting the exposed collagen in the subendothelium
In vivo
Originating or due to causes or factors within a body, organ or part
Also activated when these factors come in contact with foreign surfaces
Extrinsic pathway
Activated by tissue thromboplastin (factor 3) released from injured cells
Contributes the most to in vivo coagulation
Common pathway
Both the extrinsic and intrinsic pathways result in the formation of thrombokinase
2 major reactions: the conversion of prothrombin to thrombin by thrombokinase. Conversion of fibrinogen to fibrin by thrombin
Reaction that produces the final product of the coagulation reactions
Stages of coagulation
Stage 1: production of thrombokinase
Stage 2: thrombin formation
Stage 3: fibrin formation
Coagulation factors
Substances that are involved in the coagulation reactions
14
12- Roman numerals
2- names
13- found in the plasma
Factor III- protein found in all cell membranes and enzyme that is released when cells are damaged
13- proteins
Factor IV- calcium, plasma electrolyte
Factor I- fibrinogen
Factor IIa- thrombin important
4 mechanisms to ensure that the hemostatic plug is limited to and located at the site of injury
Products of coagulation
Adsorption of coagulation factors by platelets
Neutralization of coagulation products
Activation of fibrinolysis
Products of coagulation
Fibrinopeptides A and B inhibit platelet aggregation
Fibrin neutralizes thrombin
Adsorption of coagulation factors by platelets
Factors are adhered onto the surface of the platelets in the platelet plug
This concentrates the coagulation reactions at the site of the injury
Neutralization of coagulation products
Any fibrin or activated factors that spill away from the site of injury and enter the circulation are neutralized by: inhibitors ( antithrombin III), removal
Activation of fibrinolysis
Tissue damage results in the release of tPA which activates the fibrinolytic system
Certain products of fibrinolysis inhibit the action of thrombin
Antithrombin III
Most important inhibitor
Activated by heparin and functions to deactivate thrombin and a number of other factors
Fibrinolysis
Mechanism by which fibrin and other products of coagulation are broken down and destroyed
Limits the hemostatic mechanism and remove the hemostatic plug when it is no longer required
Substances: plasmin, FBP
Plasmin
Voracious proteolytic enzyme that destroys fibrin, fibrinogen, and factors V and VIII
Produced from the inactive pro enzyme plasminogen
Plasminogen is activated by 2 mechanisms
tPA: tissue plasminogen activator is released from injured endothelial cells
Thrombin: weak, but direct activator or plasmin
Thrombin important roles in hemostasis
Catalyzes the conversion of fibrinogen to fibrin
Acts with ADP to cause platelets in the primary plug to produce TxA2, induces secondary aggregation
Activates factor XIII which converts soluble fibrin into insoluble fibrin
Contributes to the activation of other coagulation factors
Contributes to the activation of fibrinolytic system by helping to convert plasminogen to plasmin
Fibrinogen breakdown products ( FBPs)
Produced when plasmin breaks down fibrin and fibrinogen
2 roles: inhibit thrombin, inhibit fibrin polymerization
Inhibit thrombin
FBPs bind to thrombin and prevent it from binding to fibrinogen
Inhibit fibrin polymerization
FBPs can rebind to the fibrin monomer and prevent it from binding to other fibrin monomers, slowing the formation of soluble fibrin
Antiplasmins
Present in plasma and are released by platelets during the release reaction
Deactivate plasmin when it is formed on the outer edges of the hemostatic plug
