Blood coagulation, also known as hemostasis, is the process by which blood changes from a liquid to a solid gel-like substance. It involves three stages: vasoconstriction, formation of a platelet plug, and coagulation of blood. When a blood vessel is injured, a series of reactions are initiated through the intrinsic and extrinsic pathways, ultimately resulting in a cross-linked fibrin mesh that traps blood cells to form a clot. Coagulation is tightly regulated by several mechanisms to prevent excessive clotting. Common tests evaluate the intrinsic and extrinsic pathways, as well as platelet count and function. Disorders can be inherited or acquired.

1. - Dr. E. R. Venkata Subba Reddy

2. Blood coagulation is part of an important

host defense mechanism termed
hemostasis.
 Hemostasis : arrest or stoppage of bleeding
from a blood vessel.
 Injury to a blood vessel initiates a series of
reactions resulting in hemostasis.
 Three stages : 1. Vasoconstriction
2. Formation of platelet plug
3. Coagulation of blood

3. Injury to blood vessel
↓
Endothelial damage and
collagen exposure
VonWillebrand factor → I
↓
Activation of platelets FIBRINOGEN
↓ ↓ I
Serotonin ADP + I
I TX A2 I
I ↓ I
I Aggregation of I
more platelets
I I
I ↓ ↓
Vasoconstriction platelet plug FIBRIN (clot)
(STAGE 1) (STAGE 2) (STAGE 3)

4. Definition : The process in which blood

looses its fluidity and becomes a jelly
like mass few minutes after its shed out or
collected in a container.
 The so formed mass is called clot
 The clot is a mesh of thin fibrils
entangling the blood cells .These fibrils
consist of fibrin. The fibrin is formed from
fibrinogen.

5. ENZYME CASCADE THEORY

- Factors in inactive proenzyme forms
- Series of proenzyme-enzyme conversions
( Zymogen activation reactions )
- At each stage a precursor protein
(zymogen) is converted to an active
protease by cleavage of one or more
peptide bonds
- Helped by cofactors, calcium

6. 3 STAGES

1. Formation of Prothrombin Activator
2. Conversion of Prothrombin to Thrombin
3. Conversion of Fibrinogen to Fibrin

7. Two ways

1. Contact activation pathway (formerly
known as the intrinsic pathway)
2. Tissue factor pathway
(extrinsic pathway)

8. Endothelial damage + collagen exposure
I Kallikrein & I
↓ HMW kinogen I
XII ------XIIa ↓
HMW kinogen Platelets
↓
XI ------XIa I
Calcium I
↓
IX ------------ IXa ↓
VIII & Ca Phospholipid
↓
X------------------ Xa I
I I
↓ ↓
PROTHROMBIN ACTIVATOR ( PTA )
(Xa + V + Ca +Phospholipid)

9. Tissue trauma + Tissue thromboplastin
↓
Glycoprotein
Phospholipid
I
VII --------------------------------- VIIa
I Ca
↓ Phospholipid
X ----------------------------------- Xa
I Ca
I Factor V
I Thrombin
↓
Prothrombin activator
(Xa + V + Ca +phospholipid)

10. PROTHROMBIN ACTIVATOR
I
↓
PROTHROMBIN-----------------→THROMBIN
I
↓
FIBRINOGEN a ←------------------------- FIBRINOGEN
I
Polymerization I
↓ XIII & Ca
LOOSE STRANDS OF FIBRIN-------------------------------→FIBRIN
TIGHT BLOOD CLOT

11. The substances necessary for clotting are

called clotting factors
Thirteen identified

I – Fibrinogen
II – Prothrombin
III – Thromboplastin
IV – Calcium
V – Labile factor ( proaccelerin )
VI – presence not proved
VII – Stable factor

12. VIII – Anti hemophilic factor
IX – Christmas factor
X – Stuart-Prower factor
XI – Plasma Thromboplastin antecedent
XII – Hageman factor
XIII – Fibrin stabilizing factor (Fibrinase)

13. Calcium

 Phospholipid
 Vitamin K is an essential factor to a
hepatic gamma-glutamyl carboxylase
that adds a carboxyl group to glutamic
acid residues on factors II, VII, IX and X,
as well as protein S, Protein C and
protein Z.

14. Five mechanisms keep platelet activation and the

coagulation cascade in check.
Protein C is a major physiological anticoagulant.

It is a vitamin K-dependent serine protease .
Activated by thrombin with the help of
thrombomodulin.
The activated form, along with protein S and a
phospholipid as cofactors, degrades Va and VIIIa.
Antithrombin is a serine protease inhibitor

Tissue pathway factor inhibitor(TFPI)

Plasmin cleaves fibrin into fibrin degradation products

that inhibit excessive fibrin formation.
Prostacyclin (PGI2) through cAMP inhibits platelet

activation

15. Clot consists of entrapped platelets,

RBCs, WBCs within the fibrin meshwork.
 Clot Retraction : after 30 to 45 min.
-Clot contracts. Serum oozes out.
-Actin, myosin and Thrombosthenin.
 FIBRINOLYSIS : lysis in blood vessel.
Requires plasmin (fibrinolysin)

16. Commonly used:
aPTT ( activated partial Thromboplastin time) - The

contact factor pathway
PT (also used to determine INR)- The tissue factor

pathway
Fibrinogen testing (often by the Clauss method)

Platelet count

Platelet function testing (often by PFA-100).


17. Others: Thrombin clotting time, Bleeding

time, Mixing test (whether an
abnormality corrects if the patient's
plasma is mixed with normal plasma),
Coagulation factor assays,
Antiphospholipid antibodies, D-dimer,
Genetic tests (factor V leiden),
Miscellaneous platelet function tests,
Thromboelastography (TEG or ROTEM),
Euglobulin lysis test(ELT), .

18. Platelet disorders:

-Inborn or Acquired
-congenital:
> Glanzmann’s thrombasthenia - It is
characterized by a defect in GPIIb/IIIa
fibrinogen receptor complex,
> Bernard-sourlier syndrome (abnormal
glycoprotein Ib-IX-V complex),
> Gray platelet syndrome(deficient α-granules),
> Delta storage pool deficiency(deficient dense
granules).
-Acquired: MDS, ITP, TTP, HUS, PNH, DIC, HIT.

19. HAEMOPHILIA: 3 main forms

- Hemophilia A : VIII deficiency
- Hemophilia B : IX
- Hemophilia C : XI
 Von Willebrand disease : most common
hereditary bleeding disorder . Def of
vWF, that mediates glycoprotein Ib
(GPIb) binding to collagen.

20. Thrombosis is the pathological

development of blood clots. May form an
embolus or cause occlusionocclusion by
embolus or thrombus leads to ischemic
necrosis of tissue.
 Most cases of thrombosis are due to
acquired extrinsic problems
(surgery, cancer, immobility, obesity,)
 A small proportion of people harbor
predisposing conditions known collectively
as Thrombophilia (antiphospholipid
syndrome, factor V leiden).

21. Adsorbent chemicals, such as zeolites, used for

use in sealing severe injuries quickly (traumatic
bleeding secondary to gunshot wounds).
Thrombin and fibrin glue are used surgically to

treat bleeding and to thrombose aneurysms.
Desmopressin is used to improve platelet function

Prothrombin complex

concentrate, cryoprecipitate and fresh frozen
plasma
Recoombinant activated human factor VII is

increasingly popular in the treatment of major
bleeding.
Tranexemic acid and aminocaproic acid inhibit


22. Anticoagulants and anti-platelets.

Anti platelet agents : aspirin, clopidogrel, dipyridamole

and ticlopidine; the parenteral glycoprotein Iib/IIIa
inhibitors are used during angioplasty
Anticoagulants, Warfarin (and related coumarins) and

Heparin are the most commonly used.
Warfarin affects the vitamin K-dependent clotting factors

(II, VII, IX,X).
Heparin and related compounds increase the action of

antithrombin on thrombin and factor Xa.
A newer class of drugs, the direct thrombin inhibitors, is

under development; some members are already in clinical
use (such as lepirudin).
compounds that interfere directly with the enzymatic

action of particular coagulation factors (e.g.,
rivaroxaban).

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