The coagulation system involves a cascade of enzymatic reactions that ultimately result in fibrin clot formation. The cascade can be initiated through either the intrinsic or extrinsic pathway, both of which involve a series of coagulation factor zymogens being activated into active enzyme forms. This leads to thrombin generation and conversion of fibrinogen into fibrin. A number of processes also act to regulate coagulation and prevent excessive clotting, including antithrombin III, protein C, and fibrinolysis.

1. Coagulation System
Gerald A. Soff M.D.

2. Pre-Lecture Quiz!
• Choose one or more of the following;
• 1. If I could memorize all of the bones and muscles in
the body, why can’t I remember the blasted coagulation
cascade?
• 2. O.K., so I figured out Factors
I, II, V, VII, VIII, IX, X, XI, and XII. So where the hell are
factors III, IV, and VI?
• 3. And why do they use Roman Numerals? I can’t read
my damned notes!
• 4. Who cares about this stuff anyway, I’m going into
oncology!

3. Hemostasis
• Hemostasis; “The processes of keeping the blood liquid in the
vasculature”
– Prevention of hemorrhage following vascular injury.
– Prevention of excessive clotting (thrombosis) in the vasculature.
• Primary Hemostasis;
– Vascular forces (vasoconstriction) and platelet plug
• Secondary Hemostasis;
– The coagulation factors
• Physiologic Anticoagulation processes
– Neutralize activated factors where vessels are intact.
– Fibrinolysis

4. Original Publication Of Coagulation Cascade:
Davie, E. W., and Ratnoff, O. D. (1964) Waterfall sequence for intrinsic
blood clotting. Science 145, 1310–1312

5. emedicine.medscape.com

6. Conceptual Model of Hemostasis
From Sidney Harris.

8. XII, PK, HMWK
Tissue Factor
Intrinsic XI
Pathway VII
IX, VIII Extrinsic Pathway
X, V
Common Pathway
II
Fibrinogen (I) Fibrin Monomer
XIII
Cross-Linked
Fibrin Clot

9. Coagulation Cascade
General Features
• Clotting factors (Factor II, VII, etc.) are zymogens (or
proenzymes), which are activated to an active enzyme by
limited proteolysis.
– The enzymes in the coagulation system are serine
proteinases. (Serine, Aspartic acid, Histidine amino acids
in catalytic domain)
• Cofactors of Cascade
– Factors V and VIII
• The system is a “cascade” in that there is amplification.
– One activated molecule activates multiple at subsequent
stages.
– The product of one step is an enzyme for the next step.

10. Coagulation Factors;
Enzymes

11. Serine Protease
•Serine, Aspartic acid, Histidine amino acids in catalytic domain.

12. Coagulation Factors;
Cofactors

13. XII, PK, HMWK
Tissue Factor
Intrinsic XI
Pathway VII
IX, VIII Extrinsic Pathway
X, V
Common Pathway
II
Fibrinogen (I) Fibrin Monomer
XIII
Cross-Linked
Fibrin Clot

14. Tissue Factor;
Initiation of Coagulation Cascade
 Primary process, in vivo, is the extrinsic
pathway.
 Tissue factor can be expressed by
monocytes, fibroblasts, smooth
muscle, endothelial cells.
 Tissue Factor is released in the vessel
wall, following exposure to
endotoxin, inflammation, injury.
 Tissue Factor binds/activates Factor VII
 TF:VIIa complex binds and activates Factor IX to
IXa (and to a minor degree X to Xa).

15. Tissue Factor Circulates in Cell-
Derived Microparticles.
Boulanger et al. Hypertension, 2006 Hugel et al, Physiology 20: 22-27, 2005

16. Surface Complexes of
Enzyme:Cofactor:Substrate,
The essence of the coagulation cascade
• (Modified from Furie B, Furie BC: The molecular basis of blood
coagulation. Cell 53:505, 1988.) in Hoffman’s Hematology Text.

17. Membrane-Bound TF Initiates
Coagulation Cascade

18. Procoagulant Enzyme Complexes
• Complex 1
– Tissue factor, factors VIIa, IX and X
• Complex 2 (Tenase complex)
– Factor IXa, VIII and X
• Complex 3 (prothrombinase complex)
– Factor Xa, factor V, and prothrombin
• All complexes on a negatively charged phospholipid (usually platelet)
membrane.

19. Contact System:
Initiation of Intrinsic Pathway
Factor XII, Prekallikrein, High-
Molecular-Weight Kininogen
Minimal contribution to clotting, although
it can activate Factor XI.
Possible role in blood pressure
regulation, fibrinolysis, and
inflammation.

20. Contact System:
Initiation of Intrinsic Pathway
Factor XII
Prekallikrein
High Molecular Weight
Kininogen

21. • Why do deficiencies of “Contact
Factors” not result in bleeding?
• Why do deficiencies of “Intrinsic
Pathway” lead to markedly different
severity of bleeding, (or no
bleeding)?

22. XII, PK, HMWK
Tissue Factor
Intrinsic XI
Pathway VII
IX, VIII Extrinsic Pathway
V, X
Common Pathway
II
Fibrinogen (I) Fibrin Monomer
XIII
Cross-Linked
Fibrin Clot

23. Initiation of Extrinsic Pathway By
Tissue Factor
IX
TF:VIIa VII Tissue Factor
IXa X TFPI
X Xa
 Complex of TF;VIIa can activate Factor X, but
primary procoagulant effect is via activation of
factor IX to IXa.

24. Tissue Factor
IX
TF:VIIa
Coagulation
Cascade
IXa
X TFPI
VIIIa Made
X Xa Simple
Va (And Mostly
II IIa (Thrombin)
Accurate)
Fibrinogen (I) Fibrin Monomer
XIII
Cross-Linked Fibrin Clot

25. How are Factors V, VIII, XI, XIII
Activated?

26. Thrombin Feedback;
Activation of Factors V, VIII, XI, XIII
IX Tissue Factor
XI XIa TF:VIIa
IXa
X TFPI
VIII VIIIa
X Xa
Va V
II IIa (Thrombin)
Fibrinogen (I) Fibrin
XIII XIIIa
Cross-Linked Fibrin Clot

27. Role of Factor XI
• Factor XI is component of a positive
feedback loop,
• Thrombin activates Factor XI (along
with V, VIII, and XIII), which generates
more thrombin.
• Results in augmentation of fibrin
generation.

28. VITAMIN K DEPENDENT
CARBOXYLASE
• Post-translational modification
• Factors II, VII, IX, X;
– Proteins C & S
• Converts several glutamic acid
residues to γ-carboxyglutamic acid
• Confers calcium binding and lipid
binding on these proteins.

29. CARBOXYGLUTAMIC ACID
COO- COO-COO-
CH2 O2,CO2 CH
CH2 CH2
NH3+ CH NH3+ CH
Vit K
COO- Carboxylase COO-
Glu -carboxy Glu

30. Vitamin K Mediated
-Carboxylation of Glutamic Acid

31. Vitamin K-Dependent Factors
• Factors II (Prothrombin), VII, IX, X
• Protein C, Protein S
• All are enzymes, except protein S.
• -Carboxylation of Glutamic Acid allows
for binding to calcium, and complex
formation.
• While both procoagulants and
anticoagulants are affected, the net effect
of vitamin K deficiency or antagonism is
anticoagulation.

32. Thrombin-Activatable Fibrinolysis
Inhibitor (TAFI)
• Also known as plasma carboxypeptidase B2
• TAFI is activated by
Thrombin:Thrombomodulin.
• After thrombin activation, the mature protein
down-regulates fibrinolysis.

33. Hemostatic Balance

34. Endothelial Cell-Dependent
Anticoagulant Processes
• Heparan Sulfate: AT III
• Thrombomodulin: Protein C: Protein S
• ADPase (CD39)
• Tissue Factor Pathway Inhibitor
• Nitric Oxide

35. Heparan:Antithrombin III
 Deficiency first described in 1965.
– (Egeberg O. Inherited antithrombin III deficiency causing
thrombophilia. Thromb Diath Haemorrh 13:516-30, 1965)
 AT III neutralizes the active enzymes in the coagulation
system.
 Dominant Inheritance.

36. Antithrombin III
• Antithrombin III (Antithrombin)
• When heparan sulfate (on endothelial cells) or
heparin (mast cells, pharmaceutical) binds to AT
III, the AT III undergoes a conformational change
and binds to the active enzymes of the clotting
cascade.
• Thrombin (IIa), IXa, Xa, XIa are inhibited by
Heparin/Heparan:ATIII.
– Factor VIIa is resistant to AT III.

37. Protein C/Protein S System
• Constituents;
– Protein C
– Protein S
– Thrombomodulin
– Endothelial cell protein C receptor
(EPCR
• Activated Protein C (With
cofactor Protein S) inactivates
Va and VIIIa, the cofactors of
the cascade
– (Probable role in augmenting
fibrinolysis.)
• EPCR localizes Protein C/Ca to
endothelial cell surface.
– May have role in sepsis.

38. Fibrinolytic Pathway
Plasminogen;
– Activated to Plasmin (a serine proteinase)
– Plasmin proteolyzes fibrin and fibrinogen
Plasminogen Activators;
– t-PA (Tissue-Plasminogen Activator)
• Localizes to fibrin clot
– u-PA (Urokinase-Plasminogen Activator)
• Localizes to cell membrane uPA receptor.
– Released by endothelial cells.
Inhibitors/Serpins
– PAI-1, PAI-2; Plasminogen Activator Inhibitors
– 2-Antiplasmin.

39. Fibrinolytic System Constituents

40. Fibrinolysis
Release of D-Dimer
Digestion of
tPA Plasmin Fibrin
Plasminogen
Cross-Linked Fibrin

41. Cell Surface Activation of
Plasminogen

42. Fibrin/Fibrinogen
Degradation Products

43. Fibrin/Fibrinogen Degradation Products