HEM Coagulation/ Fibrinolysis Flashcards
List 4 anticoagulant properties of endothelium
- secretion of: (prostacyclin, nitric oxide, heparin sulfate, TFPI, TPA)
- smooth surface
- Protein C receptors = inactivates Va and VIIIa
- Thrombomodulin expression = inactivates thrombin
TFPI function
Tissue Factor Pathway Inhibitor: suppresses extrinsic pathway
NOTE: anticoagulant secretion by endothelium
Thrombomodulin source + function
- an anticoagulant secretion by endothelium
- inactivates thrombin
What initiates primary hemostasis ?
vascular damage = procoagulant factors released from vessel cells, exposed collagen promotes procoagulants to begin primary hemostasis
List 5 pro-coagulant properties of damaged vasculature
- endothelial cells secrete vWF + up-regulate PLT receptors
- exposed collagen = binds vWF and PLTs
- vasoconstriction (smooth muscles contract)
- PLTs release factors (prostaglandins + prostacyclin)
- smooth muscle contain TF = activates FVII
Describe Adhesion stage of platelet plug
- reversible; PLTs BIND VESSEL WALL
a. MINOR injury = PLTs bind to collagen via GPIa/IIa, GP IV, and GP VI
b. MAJOR injury = PLTs also bind vWFv via GPIb/IX/V receptors before binding wall
Bernard Soulier
GPIb deficiency
- affects adhesion in PLT plug for MAJOR injuries
VonWillebrand Disease
vWF deficiency
- affects adhesion in PLT plug for MAJOR injuries
Describe Aggregation stage of platelet plug
- reversible OR irreversible (TXA2 and ADP)
- PLTs bind other PLTs using fibrinogen and Ca2+
- ADP released during PLT adhesion = exposes fibrinogen receptors on PLTs (GPIIb/IIIa integrin) and P-selectin
Glanzmann’s Thrombasthenia
GPIIb/IIIa deficiency
- affects aggregation in PLT plug
- reduced fibrinogen receptors on PLTs
Describe Granule Secretion stage of platelet plug
- simultaneously during adhesion/ aggregation
a. ALPHA granules = via SCC system
- PF4
- B thrombomodulin
- PDGF, endothelial GF, Transforming GF
- Factors V, XI, vWF, fibrinogen
b. DENSE = via exocytosis
- ADP/ ATP
- Ca2+, Mg2+
- serotonin
SSC = surface-connected canalicular
What blocks cyclooxygenase and prevents thromboxane A2 production ?
ASPIRIN leads to impaired PLT function
Which coagulation factors are serine proteases ?
Kallikrein
II (prothrombin)
VII
IX
X
XI
XII
Plasmin
Protein C
NOTE: must be activated/ cleaved to participate in reaction
- factors V, VIII, XIII are NOT
Which coagulation factors are cofactors ?
FV and FVIII
NOTE: presence is essential for the activity of an enzyme
Which clotting factors are vit-K dependent ? What is the function of vit K in the synthesis of these factors ?
II/ prothrombin, VII, IX, X (2790) & Protein C/ S/ Z:
- vit K catalyses carboxylation of terminal glutamic acids
- carboxyl group binds Ca2+ = allows binding of PF3
Where are the components of vWF/VIII complex produced ? What are their functions ? What cleaves the complex ?
- vWF = produced by endothelial cells; complexes with VIII = STABLE
- VIII = produced by PLT/ endothelial cells; UNSTABLE by itself
- vWF/VIII is cleaved by thrombin = VIIIa in TENASE complex
Which factors are involved in the extrinsic pathway ?
VII + TF + Ca2+ = TF:VIIa
TF:VIIa + PF3 + X = Xa
INCLUDING factors in COMMON PATHWAY
Which factors are involved in the intrinsic pathway ?
Prekallikrein + HMWK = Kallikrein
Kallikrein + HMWK = XII
XII + collagen = XIIa
XIIa + HMWK + XI = XIa
XIa + Ca2+ + IX = IXa
IXa + (VIIIa + PF3 + Ca2+) + X = Xa
Which factors are involved in the common pathway ?
X + (TENASE complex [intrinsic]/ PF3 AND TF:VIIa complex [extrinsic]) = Xa
Xa + (Va + PF3 + Ca2+) + II/prothrombin = thrombin
Thrombin + I/fibrinogen = fibrin monomer (soluble)
Thrombin + XIII = XIIIa
XIIIa + Ca2+ +fibrin monomer = fibrin CROSSLINKS (insoluble)
Function of fibrinolytic system
- normally removes fibrin clots that are no longer required
- begins hours after coagulation
- gradual enzymatic cleavage of fibrin = soluble FDPs
Plasminogen: activation
activated by TPA/ Tissue plasminogen activator
Plasminogen: mechanism of action and target
- must be activated by TPA into plasmin to cleave fibrin/ fibrinogen
- promotes fibrinolysis
Function + source of TPA
Tissue Plasminogen Activator:
- secreted by damaged endothelial cells
- promotes fibrinolysis; activates plasminogen to plasmin for cleaving fibrin = FDPs
Activation, function + location of Urokinase
- secreted by kidney
- activated by fibrin and plasmin
- promotes fibrinolysis in renal collecting ducts
Activation, function + location of Plasminogen Activator Inhibitor 1
- secreted by endothelial cells, megakaryocytes, fibroblasts, smooth muscle, monocytes, etc.
- increased in high levels of TPA
- prevents fibrinolysis; inhibits TPA and Urokinase
Function + source of α2-Antiplasmin
- secreted by liver + PLTs
- prevents fibrinolysis; irreversibly binds plasmin
Function, activation and source of TAFI
Thrombin-activatable Fibrinolysis Inhibitor:
- secreted by liver
- activated by thrombin/ thrombomodulin
- prevents fibrinolysis; prevents plasmin formation
What are FDPs ?
Fibrin Degradation Products:
- plasmin cleaves fibrin into characteristic fragments: X, Y, D, E and D-dimers
- plasmin cleaves fibrinogen into X, Y, D, E
- inhibit coagulation cascade
What is the clinical utility of measuring D-dimers ?
- measures fibrinolysis activity
- Detects DIC
Describe TFPI mechanism of action and what factors it inhibits
Tissue Factor Pathway Inhibitor:
- requires Protein S as a cofactor
- inactivates Xa by complexing into TFPI:Xa
- TFPI:FXa binds to TF:VII to prevent further activation of X
Describe the Protein C system; how is it activated ? What does it inhibit ? What is its role in fibirinolysis ?
- activated by thrombin/ thrombomodulin complex
1. Inhibits coagulation = activated Protein C combines with cofactor Protein S = Protein C:S complex inhibits Va and VIIIa
2. Promotes fibrinolysis = forms complex with/ deactivates Plasminogen Activator Inhibitor-1 (PAI-1)
Which factors does Antithrombin inhibit in coagulation ?
- activated by heparin sulfate from endothelial cell surface
- inhibits all serine proteases: Kallikrein, II/prothrombin, XII, XI, X, IX, plasmin)
What tube/ anticoagulant is used for coagulation testing ?
Sodium citrate (light-blue top)
Principle of aPPT test in vitro
Citrated plasma (light-blue top) + the addition of a contact activator, phospholipids and Ca2+ = formation of a stable clot, detected by turbidimetric end-point detection
Is an instrument that uses mechanical end-point detection prone to interference from hemolysis ? Why/ why not ?
No; it detects decreased oscillation of a steel ball in sample = clotting time
How does hemolysis affect coagulation test results, if at all ?
light to moderate: result with comment
severe: falsely decreases PT and PTT; coagulation prematurely occurs prior to testing
- check for clots at end of testing
Troubleshooting when QC = 1-3S: First and Second step
First step: re-do QC
Second step: recalibrate instrument
How does a high Hct affect coagulation test results ? How can it be corrected ?
High Hct = less plasma = sample is diluted due to excess anticoagulant (sodium citrate)
- Volume of anticoagulant in tube should be reduced
How are D-dimers measured on conventional coagulation instruments ?
- Turbidimetric immunoassays based on fragment sizes
- Particles with Ab specific for D-dimers
- Directly proportional
Factors in TENASE complex. What do they activate ?
VIIIa
PF3
Ca2+
- activates factor X
Which factors are included in the prothrombinase complex ? What do they activate ?
Va + PF3 + Ca2+
- activates prothrombin/II to thrombin
What is PF3 ? What is its role in coagulation ?
PF3 = PLT phospholipids
- during PLT activation = converted to thromboxane A2
- thromboxane A2 = triggers more Ca2+ release = promotes coagulation
Differentiate products when plasmin cleaves fibrin vs fibrinogen
Plasmin cleaves Fibrin = X, Y, D, E, D-dimers
Plasmin cleaves Fibrinogen = only X, Y, D, E
How is ZPI activated ? What does it inhibit ?
Protein Z-dependent Protease Inhibitor:
- requires cofactors (protein Z, PF3, Ca2+) to DEGRADE factor X
- by itself, it can inhibit XIa
Glycoprotien IIb/IIIa complex
- fibrinogen receptor on the platelet membrane
- It allows PLT binding of fibrinogen and vWF to bind other PLTs
Glycoprotien Ib/IX/V
- vWF receptor on the platelet membrane.
- It allows PLT binding of vWF to vascular walls for PLT adhesion.
What are the functions of platelets in hemostasis? Select all that apply:
a.
Release of serotonin
b.
Release of prostacyclin
c.
Formation of a hemostatic plug
d.
Activation of the extrinsic coagulation system
a.
Release of serotonin
c.
Formation of a hemostatic plug
Which of the following are functions of thrombin? Select all that apply:
a.
Activates factors V and VIII
b.
Activates anti-thrombin
c.
Activates Factor XIII
d.
Activates factor XI
a.
Activates factors V and VIII
c.
Activates Factor XIII
d.
Activates factor XI
