230 likes | 421 Views
MLAB 1227: Coagulation Keri Brophy -Martinez. Secondary Hemostasis Part Three. Extrinsic Pathway Activation. Cell injury releases TF into vasculature TF provides the phospholipid component where the coagulation factors interact TF complexes with Ca ++ and VIIa to activate X.
E N D
MLAB 1227: CoagulationKeri Brophy-Martinez Secondary Hemostasis Part Three
Extrinsic Pathway Activation • Cell injury releases TF into vasculature • TF provides the phospholipid component where the coagulation factors interact • TF complexes with Ca++ and VIIa to activate X
Extrinsic Pathway:Coagulation Factors • Factor III: Tissue Thromboplastin/Tissue Factor (TF) • Manufactured in most body tissues – especially lungs, brain, placenta, RBC membranes. Does not circulate unless damage occurs to tissues • Purpose : • Attracts calcium ions to help the formation of procoagulant enzyme complexes. • Converts prothrombin to thrombin
Extrinsic Pathway: Coagulation Factors • Factor VII – Proconvertin (Stabile Factor) • Produced in liver • Vitamin K dependent • Is especially sensitive to Coumadin anticoagulant therapy • Purpose • Activated by tissue thromboplastin(TF)
Extrinsic Pathway • Monitored by the Protime (PT) test • Monitors oral coagulation therapy such as coumadin, coumarin • Detects abnormalities in Factor VII, exclusively, but can also pick up deficiencies in the common pathway
Common Pathway • Activation of either or both pathways results in the conversion of factor X to Xa • In the common pathway all prothrombin is converted to thrombin, which in turn is converted to fibrin on the phospholipid surface at the site of injury.
Common Pathway • Thrombin – enzyme not normally present in plasma. Three functions: • Converts fibrinogen (I) to fibrin (Ia) • Causes potent platelet aggregation • Aids in stabilizing fibrin clot by activating Factor XIII • Activates Protein C to control the extent of clotting
Common Pathway: Coagulation Factors • Factor X – Stuart Factor (Stuart-Prower) • Produced in liver • Vitamin K dependent • Activated form acts with V, Ca++ and PF3 to form active thromboplastin
Common Pathway: Coagulation Factors • Factor V: Proaccelerin (Labile Factor) • Produced in liver • Deteriorates rapidly in room temperature • Purpose • Essential in thromboplastin formation • Increased in pregnancy & inflammation • Consumed during coagulation, not found in serum
Common Pathway: Coagulation Factors • Factor II: Prothrombin • Manufactured in the liver • Vitamin K dependent • Purpose • Upon exposure to V, Xa, PF3 and Ca++, it is converted to thrombin • Stimulates platelet aggregation in presence of Ca++
Common Pathway: Formation of Fibrin • Thrombin acts upon fibrinogen (Factor I) to form fibrin (Ia) • Fibrin clot is stabilized by Factor XIII by crosslinking the fibrin polymers
Common Pathway:Coagulation Factors • Factor I: Fibrinogen • MW = 341,000 • Normal value in plasma 200-400 mg/dl • Manufactured in the liver • Absent in serum • Purpose • Upon exposure to thrombin, forms fibrin
Common Pathway: Coagulation Factors • Factor XIII – Fibrin Stabilizing Factor • Produced in liver and platelets • Necessary to form a stable clot – causes a crosslinking of fibrin monomers
Misc: Coagulation Factors • Factor IV: Calcium • Obtained through diet and bone storage • Needed in intrinsic and extrinsic pathways • Removed by citrate • Purpose • Acts as a cofactor in many reactions of the coagulation cascade • Needed for binding to the phospholipid surface, proper platelet function, XIII activation
Misc: Coagulation Factors • There is no Factor VI
Misc. • All enzymatic reactions require a phospholipid surface, either supplied by the membranes of activated platelets (PF3) or damaged tissues (TF). This phospholipid requirement limits coagulation reactions to the site and prevents clotting.
HELP!!! How Will I Ever Get This Down…. 1. Simplified enzymatic coagulation event VIII V XII ----XI---IX------X---------II-------IIa--------I VII
Next steps… • Change the sequence to Arabic numerals 8 5 12—11—9—10—2—T –1 7 **”T”= thrombin
Learning the PT/PTT Pathways 8 5 12—11—9—10—2—T –1 7 **”T”= thrombin PT PTT
Vitamin K Dependant Factors C s s 8 5 12—11—9—10—2—T –1 7 **Think of the central core for those requiring Vitamin K. Protein C and S also require Vitamin K. Protein C inhibits factors 8 and 5. Indicated by “X”
Extended Coagulation sequence 8 5 12—11—9—10—2—T –1 7 13
Misc. 8 5 12—11—9—10—2—T –1 7 Thrombin sensitive factors Factors destroyed by plasmin Factors found in platelets 13
References • McKenzie, Shirlyn B., and J. Lynne. Williams. "Chapter 30." Clinical Laboratory Hematology. Boston: Pearson, 2010. Print.