Overview of Coagulation- Exam 1 Flashcards
(103 cards)
1
Q
What is the purpose of blood circulation “checks and balances”?
A
Preserve blood fluidity
Seal off site of bleeding
Balance anticoagulant/procoagulant factors
2
Q
Anticoagulant Factors
A
Released by endothelial cells
Ex. prostacyclin, vascular plasminogen activator
3
Q
Procoagulant Factors
A
Platelets
Plasma proteins- inactive state (zymogen)
release of lining when vascular hose gets disrupted
4
Q
Zymogen
A
Inactivate state of plasma proteins
5
Q
When does the intrinsic pathway come into play?
A
In vitro (not in vivo) Ex. in the ECC
6
Q
3 Phases of Cell-Based Coag Model
A
Initiation
Amplification
Propagation
7
Q
What is the most significant event to initiate coagulation?
A
FVIIa/TF complex activity (Initiation Phase)
8
Q
What is TF?
A
Tissue factor, a membrane-bound protein exposed to plasma during vascular damage
Receptor and cofactor for FVII
9
Q
What happens when FVII (zymogen) is bound to TF?
A
TF converts FVII to FVIIa to create FVIIa/TF complex
10
Q
Where is FXa formed in the initiation phase?
A
ON the cell; remains on cell surface
11
Q
What zymogens does FVIIa/TF complex activate?
A
FX and FIX
12
Q
What happens with TF-bearing cells in the absence of injury?
A
TF-bearing cells bind FVIIa, low level FIXa, low level FXa
*BUT separated from amplification components by normally intact blood vessel wall
13
Q
What is the purpose of the small amt of thrombin generated on the TF-bearing cell?
A
Serves as the “signal” for Phase II: Amplification to begin
14
Q
FIIa
A
Thrombin
15
Q
FII
A
Prothrombin
16
Q
What happens when sufficient thrombin (FIIa) is generated on or adjacent to TF-bearing cells?
A
Platelets are activated
17
Q
What does the small amt of TF-bearing cell-generated thrombin do?
A
- Activates Platelets
- Activates FVa from FV
- Activates FVIIIa and dissociates it from vWF
- Activates FXIa from XI
18
Q
What is the first step in phase III: propagation?
A
Production of vast amounts of thrombin on the surface of activated platelets
19
Q
What happens when vascular injury occurs?
A
- Platelets leave blood vessel
- Platelets bind to collagen/vWF/vessell wall receptors
- Platelets activated by factors and priming thrombin
20
Q
What is the first step in the formation of the platelet “plug” necessary for primary hemostasis?
A
The adherence of platelets to the damaged tissue
21
Q
What factors form the the platelet tenase complex?
A
FVIIIa and FIXa
22
Q
When is most of the thrombin produced generated?
A
AFTER the initial fibrin clot is formed
23
Q
What does the exposive amt of thrombin produced do?
A
Continues to activate FXIII and other factors
Helps to keep constructing the platelet/thrombin clot
24
Q
Arterial circulaton
A
requires rapid response system to seal bleeding sites
platelets take leading role followed by fibrin formation
25
What agents are used to prevent coronary thrombosis in arterial circulation?
Antiplatelet agents
26
Venous circulation
slower response acceptable
| rate of thrombin generated takes leading role
27
What agents are used to prevent DVT in venous circulation?
Antithrombin agents
28
What happens when an arterial blood vessel is damaged?
Vascular constriction
Platelet adhesion/activation (platelet plug)
Activation of cell-based coagulation cascade--> fibrin clot
Clot retraction
Activation of fibrinolytic cascade
Vessel repair/regeneration
29
What happens when the blood vessel itself is injured?
Persistent constriction of smooth muscles
| Most prominent following severe crushing type injuries
30
Describe the layers in an artery.
Most have 2 layers (except uterine artery)
Inner-circular
Outer-longitudinal
31
Shear stress for larger arteries
500/sec
32
shear stress for arterioles
5,000/sec
33
Shear stress is __________ related to flow velocity.
Inversely
34
Why does shear stress make platelet adhesion a problem?
Opposes any tendency of flowing blood to clot
Limits time available for procoagulant reactions to occur
Displaces cells or proteins not tightly bound to the vessel wall
35
Coaxial migration
Platelets pushed to the vessel perimeter by larger erythrocytes and leukocytes- which are in the center
Flow is slower along the edges and faster in the center
36
What binding sites does "capture" of platelet adhesion depend on?
Subendothelial molecules of vWF and collagen
| Platelet surface receptor Glycoprotein Ib (GPIb)
37
Glycoprotein Ib
Platelet surface receptor
Makes cells "sticky"
Low-affinity interaction with vWF, binds easily
38
What holds vWF in place?
vWF binding to subendothelial collagen
39
What happens when platelet GPIb interacts with vWF?
Transmembrane Signaling; which coupled with high shear stress results in activation of the platelet.
40
What happens when a platelet is activated?
Platelet loses normal discoid shape
Plt receptor GPIIb/IIIa undergoes calcium-dependent conformational change
GPIIb/IIIa binds with vWF (high-affinity)/or fibrinogen
Collagen binds w. plt receptor GPIa/IIa
Collagen binds w. plt receptor GPIV --> activation
41
What kind of bond is GPIb and vWF?
Low affinity interaction
42
What kind of bond is GPIIb/IIIa and vWF?
High affinity bond
43
Subendothelial collagen bond with GPIa/IIa
at medium shear stress strong enough to bind platelet to subendothelium
44
What are the goals of platelet activation?
Recruit of additional platelets
Vasoconstriction of smaller arteries
Local release of ligands needed for stable platelet-platelet matrix
Localization and acceleration of platelet-associated fibrin formation
Protection of clot from fibrinolysis
45
What do activated platelets release?
Thromboxane
Serotonin
ADP
46
Thromboxane A2 (TXA2) and where is it formed?
Platelet agonist and vasconstrictor
Formed in cytosol following cyclooxygenase cleavasge of arachidonic acid (cyclooxygenase activity irreversibly inhibited by aspirin-no TXA2 formation)
47
What will irreversibly inhibit cyclooxygenase activity?
Aspirin
48
Serotonin
release from platelet granules
| platelet agonist and vasoconstrictor
49
Adenosine Diphosphate (ADP)
release from platelet granules; platelet agonist no known vasoactive role
Strong recruiter and activator of platelets
50
Why should you not use platelet gel on coronary arteries?
Induce profound arterial constriction
| Grafts will shut down, st segements go up and induce a heart attack
51
Where are fibrinogen and vWF stored?
Alpha-granules within platelet
| Release following activation
52
What creates a tight matrix between the platelets?
Fibrinogen and vWF bonds form between platelets
53
How many GPIIb/IIIa receptors are present on the platelet surface?
More than 50,000
| Additional receptor molecules are available within cytoplasm
54
What are some additional clotting factors?
```
Prekallikein
High molecular weight kininogen
AT; ATIII
Lipoprotein-associated coag inhibitor (extrinsic pathway inhibitor)
Antiplasmin
Plasminogen activator inhibitor
Alpha2-Macroglobulin
Protein C
Protein S
```
55
What is an extrinsic pathway inhibitor example?
Lipoprotein-associated coagulation inhibitor
56
When is the termination system initiated to disrupt the clotting process and the clot itself?
As the fibrin clot is being formed
57
4 autologous anticoagulants that help control the spread of coagulation activation
```
Tissue Factor Pathway Inhibitor (TFPI)
Protein C (PC)
Protein S (PS)
Antithrombin III (AT or ATIII)
```
58
What does TFPI do?
Forms a quarternary complex called TF/FVIIa/FXa/TFPI which inactivates various factors and limits coagulation
59
What do proteins C and S do?
Proteins C and S inactivate FVa and FVIIIa cofactors
| S is a helper; makes C work better
60
Protein C
Vitamin K-dependent plasma glycoprotein which helps break down FVa and FVIIIa
61
How is Protein C activated?
Thrombin (negative feedback loop?) and its activity is increased by PS (which is also vitamin K-dependent)
62
What does AT do?
Inhibits thrombin and the Serine Proteases such as FIXa, FXa, FXIa, and FXIIa
63
Examples of Serine Proteases
FIXa, FXa, FXIa, and FXIIa
64
What signals the fibrinolytic phase of coagulation?
The production of plasmin
65
How is plasmin produced?
Produced from zymogen plasminogen by the urokinase-type activator (uPA) and tissue-type plasminogen activator (tPA)
66
How are uPA and tPA regulated?
Regulated by plasminogen activator inhibitors 1 and 2 (PAI-1 and PAI-2)
67
What activates tPA?
Thrombin and venous occlusion (negative feedbackloop)
| Released by endothelial cells
68
Fibrin Degradation Products
Cleaved fibrin result
FDPS; Fibrin split products
Measured to determine DIC, amt of fibrinolysis occurring
69
What activates Plasminogen to turn into Plasmin?
Extrinsic: tPA, uPA
Intrinsic: FXIIa, HMWK, kallikrein
Exogenous: streptokinase
70
Endothelial Cells as Endogenous Anticoagulant
Negative charge repels platelets
Release NO and prostacyclin (PGI2) which inhibit platelet adhesion and aggregation
Release ADPase
71
Nitric Oxide
Endothelium- derived relaxant factor
72
ADPase
inactivates platelet released ADP limiting ability to recruit other platelets
73
Effects of coag on CPB
Bleeding
Circuit Integrity
Inflammation
Disease state of patient
74
Bleeding on CPB
Bad outcome; increased cost; increase exposure to blood products; increased chance of infection
75
Circuit integrity on CPB
large foreign surface stimulates coagulation cascade; concerned with coagulation monitoring, treatment of circuit surface/protocols
76
Inflammation on CPB
coagulation cascade will stimulate inflammation activities
77
what patient conditions will affect coagulation status?
Diabetes; liver disease, DIC, obesity, sepsis
78
Effects of CPB on Coagulation
Activates intrinsic and extrinsic coagulation pathways
Activates neutrophils and monocytes-->leukocytes
Expose subendothelium--> coagulation
Platelet activation
Vascular endothelial cell activation
79
Coronary Suction on Bypass
introduces TF form damanged cells
| Activates extrinsic pathway
80
Negatively Charged Surface affect on Bypass
Activates intrinsic pathway
| Activates fibrinolysis--> complement system
81
What causes bleeding?
```
Mechanical
Insufficient fibrin formation
Insufficient clot integrity
Insufficient clot adhesion
Fibrinolysis
```
82
Antiplatelet agent
Aspirin (treats stroke/thrombosis)
83
Antithrombin agent
heparin, warfarin (treats DVT)
84
Gold standard for measuring soluble coagulation
PT (guide warfarin dosing) and aPTT (guide heparin dosing)
85
How much of total thrombin generated during clotting process occurs in the propagation phase?
96%
86
Most common lab test of soluble coagulation measure kinectics of what phase only?
Initiation Phase; even though most thrombin is generated in the propagation phase
87
In PT and aPTT, the appearance of fibrin gel indicates what percent completion of the total reaction?
<5%
88
Intrinsic Tenase Complex composed of what factors
FVIIIa/IXa complex
89
Hemophilia A
Lacks FVIII
90
Hemophilia B
Lacks FIX
91
Extrinsic Tenase Complex composed of what factors
TF/VIIa complex
92
Extrinsic Tenase vs Intrinsic Tenase Efficacy
Intrinsic Tenase shows 50-fold increase in efficacy than extrinsic tenase generation
93
Rxn on platelet membrane vs free proteases
Assembly of entire rxn on platelet confers 13-million fold increase in catalytic efficiency over proteases free in solution
94
Prothrombinase promotes prothrombin activation rate enhancement ________fold > free FXa on prothrombin
300,000 fold
95
What is the rate-limiting reagent in prothrombin cleavage? (Forming thrombin)
Platelet Bound FXa
96
In vitro, platelets must drop how much before prolongation in time of clot formation?
< 10,000/uL
97
In surgery, thrombocytopenia can produce arterial bleeding at higher platelet counts of how much?
~50,000/uL
98
Shear rates at ateriosclerotic plaques of 50% stenosis reach ....?
3,000 to 10,000/sec
99
Platelets circulate for how many days?
7 to 10 days
100
Bernard-Soulier Syndrome
deficient in platelet receptor GPIb, 50% receptor density
101
What is the major adhesive ligand participating in matrix formation in venous clots?
Fibrinogen
102
_____% of fibrin stabilizing activity in blood resides in platelets released at sites of bleeding.
50%
103
disintegrins
compete with fibrinogen and vWF for binding sites on platelet GPIIb/IIIa receptors; platelet anesthetic
