This document provides an overview of the coagulation system. It begins with an introduction to the coagulation cascade and hemostasis. It then discusses the intrinsic and extrinsic pathways in more detail, focusing on the complexes formed and the factors involved such as tissue factor and thrombin. The document also covers anticoagulation processes mediated by the endothelium like heparan sulfate and protein C. It concludes with explanations of fibrinolysis and the role of vitamin K in carboxylating coagulation factors.

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

2. Coagulation Cascade

Choose one or more of the following;

1. If I could memorize all of “CDs”, 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 is
factor 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!



2

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
3

4. A Series Of Perspectives On The
Coagulation System/Cascade
4

5. Original Publication Of Coagulation Cascade:
Davie, EW & Ratnoff, OD. (1964) Waterfall sequence for intrinsic blood
clotting. Science 145, 1310–1312
5

6. emedicine.medscape.com
6

7. Conceptual Model of Hemostasis
From Sidney Harris.
7

8. 8

9. Contact
System
XII, PK, HMWK
Tissue Factor
XI
Intrinsic
Pathway
VII
IX, VIII
Extrinsic Pathway
X, V
II
Fibrinogen (I)
Common Pathway
Fibrin Monomer
XIII
Cross-Linked
Fibrin Clot
9

10. Coagulation Factors;
Enzymes
10

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

12. 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”, i.e. waterfall.
– One activated molecule activates multiple at subsequent
stages.
– The product of one step is an enzyme for the next step.
12

13. Coagulation System Is Best Understood As
Series of Membrane-Bound Complexes:
Enzyme/Cofactor/Substrate

(Modified from Furie B, Furie BC: The molecular basis of blood coagulation.
Cell 53:505, 1988.) in Hoffman’s Hematology Text.
13

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).

14

15. Tissue Factor (TF) Expression In The
Vessel Wall.
 45 kDa transmembrane glycoprotein
 Expressed in blood vessels
Adventitia
 Brain
 Lung
 Placenta

Mackman N, The Role of Tissue
Factor and Factor VIIa in
Hemostasis. Anesth Analg
2009;108:1447–52.
15

16. Membrane-Bound TF Initiates
Coagulation Cascade
Enzyme: VII
Cofactor: TF
Substrate: Factor IX, Factor X
16

17. Procoagulant Enzyme Complexes

Complex 1
– Tissue factor, VIIa, IX and X

Complex 2 (Tenase complex)
– IXa, VIIIa, and X

Complex 3 (prothrombinase complex)
– Xa, Va, and prothrombin (II)

All complexes on a negatively charged phospholipid (usually
platelet) membrane.
17

18. Procoagulant Enzyme Complexes
Enzyme
Cofactor
Substrate
Product
TF:VII
VII/VIIa
Tissue Factor
IX, X
IXa, Xa
Tenase complex
IXa
VIIIa
X
Xa
Prothrombinase
complex
Xa
Va
II
(Prothrombin)
IIa
(Thrombin)
18

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.
19

20. Fibrinogen Cleavage by Thrombin and
Cross-Linkage of Monomers By F XIIIa

http://emedicine.medscape.com/article/960677-overview
20

21. XII, PK, HMWK
Intrinsic
Pathway
Tissue Factor
XI
VII
IX, VIII
Extrinsic Pathway
V, X
Common Pathway
II
Fibrinogen (I)
Fibrin Monomer
XIII
Cross-Linked
Fibrin Clot
21

22. So You Think You Understand The
Coagulation System?
don’t deficiencies of “Contact
Factors” result in bleeding?
 Why do different deficiencies of
“Intrinsic Pathway” factors lead to
markedly different severity of
bleeding, (or no bleeding)?
 Why
22

23. XII, PK, HMWK
Intrinsic
Pathway
No bleeding
Factor XI Deficiency:
Mild to no bleeding
XI
IX, VIII
Hemophilia A, B:
Severe Bleeding
V, X
II
Fibrinogen (I)
Fibrin Monomer
XIII
Cross-Linked
Fibrin Clot
23

24. Tissue Factor:VIIa “Crosses” Arms
Of The Coagulation Cascade To
Activate Factor IX
IX
TF:VIIa
IXa
X

X
VII
Tissue Factor
TFPI
Xa
Complex of TF;VIIa can activate Factor X, but
primary procoagulant effect is via activation of
factor IX to IXa.
24

25. Tissue Factor
IX
TF:VIIa
IXa
X TFPI
VIIIa
X
Xa
II
Fibrinogen
(I)
Va
IIa (Thrombin)
Coagulation
Cascade
Made
Simple
(And Mostly
Accurate)
Fibrin Monomer
XIII
Cross-Linked Fibrin
Clot
25

26. How are Factors V, VIII, XI, XIII
Activated?
26

27. Thrombin Feedback;
Activation of Factors V, VIII, XI, XIII
Tissue Factor
IX
XI
XIa
TF:VIIa
X TFPI
IXa
VIII
VIIIa
X
Xa
Va
V
IIa (Thrombin)
II
Fibrinogen (I)
XIII
Fibrin
XIIIa
Cross-Linked Fibrin Clot
27

28. 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.
Deficiencies not as sevee as VIII, IX, but more
clinically relevant than XII, Prekallikrein, High
Molecular Weight Kininogen.
28

29. 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

30. CARBOXYGLUTAMIC ACID
COO-COO-
COOCH2
O2,CO2
CH2
CH2
NH3+ CH
COOGlu
CH
Vit K
Carboxylase
NH3+ CH
COO-carboxy Glu
30

31. Vitamin K Mediated
-Carboxylation of Glutamic Acid
31

32. 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

33. Hemostatic Balance
33

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

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.
35

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.
36

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.
37

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.
38

39. Fibrinolytic System Constituents
39

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

41. Fibrin/Fibrinogen
Degradation Products
41

42. 42

43. 43

44. 44

45. http://thrombin.nl/files/img/knowhow2/thromb2.jpg
45