Diagram the in vitro coagulation pathways (intrinsic and extrinsic).
Intrinsic:
12 —> 11 —> 9 —(with 8 + Ca)—> [10 —(with 5 and Ca)—> 2 —(with Ca)—> fibrinogen to fibrin —(with 13)—> cross-linked fibrin]
(12, 11, 9 with 8 to [10, with 5 to 2, fibrinogen to fibrin, with 13 forms cross-links])
Extrinsic:
TF + 7 —> [10 —(with 5 and Ca)—> 2 —(with Ca)—> fibrinogen to fibrin —(with 13)—> cross-linked fibrin]
Diagram the in vivo (“new”) coagulation pathway.
TF + 7 —> 9 —(with 8)—> 10 —(with 5)—> 2(prothrombin to thrombin) —> fibrinogen —> fibrin monomers —> fibrin polymers —(with 13)—> fibrin clot
(TF and 7 to 9, with 8 to 10, with 5 to 2, fibrinogen to fibrin monomers then polymers, with 13 to fibrin clot)
Explain how PT tests are performed.
Measures EXTRINSIC pathway
Plasma + TF + Ca + phospholipids -> measure time to clot
Normal = 12-14 seconds
Explain how PTT tests are performed.
Measures INTRINSIC pathway
Plasma + contact activator + phospholipid -> wait 5 min -> add CaCl2 -> measure time to clot
Normal = 23-33 seconds
Name the four stages of hemostasis and explain what is occurring in each.
- Reflex vasoconstriction at site of injury
- Neurogenic mechanism via local release of chemical mediators - Platelets come to site of action
- VWF (von Willebrand factor): platelets adhere to sub-endothelial matrix via VWF
- Platelets become activated: increase surface area, aggregate - Coagulation cascade forms a clot
- Tissue factor starts the coagulation cascade
- See thrombin activation and fibrin polymerization - Thrombus and antithrombotic events
- Endothelium releases t-PA, thrombomodulin, trapped neutrophils and RBCs
Explain the 3 A’s associated with the role of platelets in hemostasis.
Their role in primary hemostasis–
Adhesion - VWF mediates adhesion to subendothelium at site of injury
Activation - metabolic activity increases secretion, increases surface area, and results in surface protein GPIIb/IIIa alteration
Aggregation - fibrinogen cross-links the GPIIb/IIIa, mechanical contraction occurs via actomyosin, surface phospholipid exposed
Name three functions of von Willebrands factor.
- Adhesion - undergoes conformational change on binding to sub-endothelial collages -> binding to platelet GP1b
- Aggregation - binds platelet GPIIb/IIIa
- Factor 8 binding - binds factor 8 to site of hemorrhage, protects from cleavage
Explain the role of factor 13 in coagulation.
Stabliizes the fibrin clot by cross-linking the lysine and glutamine side chains
Name the three inherent anticoagulant systems/mechanisms in the blood.
- Antithrombin: binds heparin-like molecules, makes conformational change so they can bind thrombin (IIa)
- Effect: neutralize master regulator -> neutralize everything - Thrombomodulin: binds thrombin and protein c -> APC, which is antithrombotic
- APC binds protein S -> inactivates factors 5 and 8 - Fibrinolytic system: functions in clot lysis
- Plasminogen (from liver) activated by…
- —Tissue plasminogen activator (from endothelial cells) at clot site, bound to fibrin
- —Urokinase-PA
- —Streptokinase
- …to plasmin, a serine protease
- —Cleaves fibrin –> D-D dimer, other fragments
Identify four types of hemophilia and the factors that are deficient in each.
von Willebrand’s disease: VWF
Hemophilia A: Factor 8
Hemophilia B: Factor 9
Hemophilia C: Factor 11
Name the three components of “Virchow’s triad” active in thrombosis.
- Endothelial injury
- Alterations in blood flow
- Hypercoagulability
Explain the abnormality present in factor V Leiden hypercoagulability.
AA change in Activated Protein C (APC) cleavage site on Factor 5a molecule -> APC cannot inactivate it
Factor 5 persists longer -> increased thrombin generation -> hypercoagulable state
Worsened with OCP
Discuss the etiological, clinical, and laboratory findings associated with DIC.
DIC: disseminated intravascular coagulation; a pathologic, consumptive coagulopathy
Widespread, inappropriate coagulation in microvessels -> thrombosis -> consumption of procoagulants -> hemorrhage
Laboratory:
- -Thrombocytopenia
- -Prolonged screening coagulation tests
- -Elevated fibrin degradation products (D-dimer)
- -Fragmented red blood cells
Calculate an INR from a patient’s PT value and the normalized PT value.
INR: international normalized ratio
—Target = 2-3
INR = (patient PT/mean normal PT for lab) ^ ISI
ISI = international sensitivity index
Higher ISI = less sensitive reagent
Explain the mechanism behind three forms of antiplatelet (may not need to know).
Aspirin: irreversibly inhibits COX-1 in platelets (would otherwise make thromboxane A2)
NSAIDs reversibly inhibit COX-1
Clopidogrel/Plavix block ADP receptor
Abciximag blocks GPIIb/IIIa
Hemostasis
Maintenance of blood in a fluid, thrombus-free state under normal conditions
Induce a rapid and localized hemostatic plug at a site of vessel injury
Thrombosis
Inappropriate clot formation, a pathologic process
Procoagulants
Clot promoting components of blood and blood vessels
Anticoagulants
Clot inhibiting or clot dissolving components of blood or blood vessels
Primary hemostatic plug
Initial phase of cessation of bleeding
Brought about at the site of vessel injury by adhesion and aggregation of platelets to vessel wall and to other platelets
Secondary hemostatic plug
The stabilization of the primary hemostatic plug by the generation of fibrin from plasma proteins
Coagulation cascade
A series of sequential, enzymatic conversions turning proenzymes into activated enzymes culminating in the formation of fibrin
Fibrinolysis
The controlled breakdown and remodeling of fibrin at the site of thrombus formation to reestablish blood flow in an affected blood vessel
Thrombophilia
Hereditary and acquired defects, primarily in anticoagulant components of the blood, which result in increased risk for thrombosis
