2. Objectives.
1. To appreciate the clinical import.
2. To appreciate the basic chemistry of mediators.
3. To understand the physiology of hemostasis.
4. To highlight clinical conditions
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OLAGBENRO: overview of haemostasis-2
6. Definitions.
Part of cardio-vascular and immunological
homeostasis.
Maintain vessel patency and vessel wall integrity.
Carefully choreographed symphony with feedback
and feed-forward agents.
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OLAGBENRO: overview of haemostasis-2
7. Prevalence
*Registers of Haematology Dept NHA
7
50% of ward consults (19 of 38)*.
17% of cumulative clinic visits (85 of 493)*.
9% of admissions (9 of 54)*.
VTE most common.
UCH: 35.6 patients/year with VTE
(Kotila et al, Afr J Med Med Sci. 2013 Jun;42(2):177-81).
Autopsies may detect missed cases.
8. Components of hemostasis.
OLAGBENRO: overview of haemostasis-2
8
Blood vessels.
Platelets.
Coagulation factors.
Inhibitors of coagulation.
Fibrinolysis.
9. In summary (role of stasis)
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OLAGBENRO: overview of haemostasis-2
10. Hemostasis -1.
Balance between
Pro- and anti-coagulation
mediators
Pro- and anti-fibrinolytic
mediators.
Balance can be upset if any
components are
Inadequate
Excessive
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OLAGBENRO: overview of haemostasis-2
11. Hemostasis -2.
OLAGBENRO: overview of haemostasis-2
11
Development of thrombi
Excessive local or
systemic activation of
coagulation
Sustained bleeding
Excessive local or
systemic fibrinolytic
activity
14. Clotting Factors –chemistry.
OLAGBENRO: overview of haemostasis-2
14
Schema of
categorization:
Substrate –fibrinogen
(Factor I): main
substrate, makes fibrin
Co-factors –
accelerate enzymatic
reactions (factors V and
VIII, HK, S, and C)
Enzymes
• Serine proteases in
active form
• Transaminase in active
form
15. Contact proteins
OLAGBENRO: overview of haemostasis-2
15
Factors XII, and XI,
Prekallikrein (PK), and
Kininogen (HMWK).
Involved in earliest
phases of clotting
Partially consumed
during coagulation
Found in serum
Also involved in
Fibrinolysis, kinin
formation, activation of
complement,
inflammation.
Congenital
deficiencies often
asymptomatic,
except XI deficiency
which usually results in
a mild bleeding disorder
16. Prothrombin Group
OLAGBENRO: overview of haemostasis-2
16 Vitamin-K
Dependant Clotting
Factors.
Factors-II, -VII, -IX, -
X, Prt C and S (and
Z).
All contain γ-
carboxyglutamic acid
• Critical for Ca++
binding
properties.
• Need Ca++ to
bind to
phospholipid
surface
All but Factor-II
found in serum.
Vitamin K
antagonists
(Warfarin and
Coumadin) inhibit
the Vitamin K
dependent
carboxylation of
glutamic acid
17. Fibrinogen Group
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17
Thrombin-Sensitive Clotting Factors
Factors I (fibrinogen), -V, -VIII, and –XIII
All are acted upon by thrombin in the process of
blood coagulation
None found in serum
20. Clotting Factors-3.
Factor Half life (hours) Comment
II 65 Prothrombin group.
VII 5 Vitamin K needed
IX 25 For synthesis
X 40 Require Ca² for activation
I 90 Thrombin interacts with
them
V 15 Increase in pregnancy,
VIII 10 Inflammation, OCP use.
XI 45
XIII 200
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OLAGBENRO: overview of haemostasis-2
24. Cell theory of coagulation.
OLAGBENRO: overview of haemostasis-2
24
New understanding. Explains in-vivo & in-vitro.
Stages.
Initiation. Amplification. Propagation. (Cessation).
Cell surfaces and factors.
Platelet phospholipids & Factor-2.
Role of thrombin.
25. OLAGBENRO: overview of haemostasis-2
25
Initiation phase:
Tissue factor (TF) is released
from injured tissue cells,
endothelial cells and
monocytes.
TF and Factor VIIa form the
TF / Factor VIIa complex.
TF / Factor VIIa activates a
small amount of Factor IX
and X to generate a small
amount of thrombin.
Factor XII (and other
“contact” factors) play a
minor role in the activation
of Factor XI.
Amplification phase
Thrombin activates Factor V
to Va,
Factor VIII to VIIIa and
activates more platelets.
Thrombin also activates FXI
to FXIa.
26. OLAGBENRO: overview of haemostasis-2
26
Propagation phase:
Additional Factor Xa is produced when TF / Factor VIIa
complex activates Factor IX.
The resultant Factor IXa along with Factor VIIIa forms the
tenase complex which then
converts more Factor X to Xa.
Factor Xa and Va along with calcium and a phospholipid
(PL) surface (activated platelets) form the prothrombinase
complex which converts
prothrombin (Factor II) to large amounts of thrombin
(Factor IIa).
28. 3 stages of conversion of fibrinogen to fibrin
Proteolysis
Thrombin cleavage of fibrinogen results in fibrin monomers
Polymerization
Spontaneous self-assembly into fibrin polymers
Stabilization
Introduction of covalent bonds into fibrin polymers by XIIIa
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29. Inhibition of coagulation
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29
Thrombin binds to the membrane
receptor thrombomodulin and
activates Protein C to Activated
Protein C (APC).
APC combines with its co-factor
Protein S which then inhibits
Factors Va and VIIIa, slowing down
the coagulation process.
Thrombin bound to
thrombomodulin becomes inactive
and can no longer activate
procoagulant factors or platelets.
The endogenous anticoagulant,
antithrombin inhibits the activity of
thrombin as well as several of the
other activated factors, primarily
Factor Xa.
33. Fibrinolysis.
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33
Tissue plasminogen activator
(t-PA) converts plasminogen
to plasmin
which breaks down cross-
linked fibrin to several fibrin
degradation products,
the smallest of which is D-
dimer.
Thrombin activatable
fibrinolysis inhibitor (TAFI)
prevents the formation of
plasmin.
Anti-plasmin and
plasminogen activator
inhibitor-1 (PAI-1) inhibit
plasmin and t-PA
respectively.
34. Plasminogen activators
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34
Tissue PA
endothelial cells
arm>legs
Increased by venous
occlusion, exercise,
thrombin, adrenaline,
vasopressin.
Binds lysin residues on
fibrin or to tPAI and
cleared by the liver.
uPA(urokinase):
renal tubules and GIT.
activated by kallikrein.
Exogenous PA:
snake venom, saliva of
vampire bats,plants and
microorganisms like b
haemolytic streptococci.
bind plasminogen and then
activates other
plasminogen.
35. Inhibitors of fibrinolysis
tPAI:
Type I- secreted by the endothelium, also in platelets and
granulocytes.
Type 2- placenta, monocytes and epidermal cells.
Inhibitors of plasmin: serine proteases, chief among
these is a2 antiplasmin
38. Factors affecting test results
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38
Blood collected into incorrect type of tube (not a sodium
citrate tube).
Incorrect plasma to citrate ratio (e.g. under filling of tube or
patient’s hematocrit > 0.55 L/L).
Heparin contamination of sample (e.g. incorrect order of draw
or sample taken from central lines).
Clotting in tube from traumatic venipuncture or inadequate
mixing.
Hemodilution of sample