Thrombosis is the formation of a blood clot or thrombus inside a blood vessel. It occurs due to endothelial injury, altered blood flow, and hypercoagulability. The clotting process involves platelet activation and conversion of fibrinogen to fibrin. Thrombosis can cause ischemic injury or thromboembolism if parts of the clot break off and travel to other sites. Risk factors include atherosclerosis, hypertension, diabetes, smoking, and hereditary hypercoagulable states. Thrombi are classified as arterial or venous depending on their location and composition.

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2. DEFINITION
• Process of formation of solid mass in circulation from the constituents of
flowing blood the mass itself is called a thrombus.
Characterised by
• activation of platelets
• the process of clotting involves only conversion of soluble fibrinogen to
insoluble polymerised fibrin
• Harmful effects:
1. Ischaemic injury
2. Thromboembolism
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3. (Virchow's triad)
• 1. endothelial injury
• 2.altered blood flow
• 3.hypercoagulability
of blood - activation
of platelets and of
clotting system
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4. 1.ENDOTHELIAL INJURY -blood vessel wall is
important for maintaining normal blood flow
1. protects the flowing blood from
thrombogenic influence of subendothelium.
2.few anti-thrombotic factors
Heparin - inactivates some other clotting
factors
 Thrombomodulin
 Inhibitors of platelet aggregation
 Tissue plasminogen activator
3 .few prothrombotic factors
a) Thromboplastin or tissue factor
b) von Willebrand factor
c) Platelet activating factor
d) Inhibitor of plasminogen activator
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5. • Vascular injury exposes the subendothelial
extracellular
matrix or ECM
• (e.g. collagen, elastin, fibronectin, laminin and
glycosaminoglycans) which is thrombogenic
• important role in initiating haemostasis as well as
thrombosis
• Injury to vessel wall also causes vasoconstriction of
small blood vessels to reduce the blood loss
• Endothelial injury is of major significance in the
formation of arterial thrombi
• thrombi of the heart, especially of the left ventricle
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6. • A number of factors and conditions may cause
vascular injury
• predispose to the formation of thrombi
1. Endocardial injury - cardiac surgery
2.Ulcerated plaques - advanced atherosclerosis.
3.Haemodynamic stress - hypertension.
4. Arterial diseases.
5. Diabetes mellitus.
6. Endogenous - hypercholesterolaemia,
7. Exogenous - cigarette smoke
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7. 3. ROLE OF PLATELETS - Following
endothelial cell injury, platelets come to
play a central role in normal
haemostasis as well as in thrombosis
1. Platelet adhesion - Glycoprotein Ib
(GpIb) receptor (Primary
aggregation)
2. Platelet release reaction - platelet
granules are released to the
exterior.
• Two main types of platelet granules
are released:
1. Dense bodies
2. Alpha granules
3. Platelet aggregation- release of ADP,
a potent platelet aggregating agent
(secondary aggregation)
4. ROLE OF COAGULATION SYSTEM
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8. 4. ALTERATION OF
BLOOD FLOW
Turbulence(irregular ) and
stasis occur in thrombosis
in which the normal axial
flow of blood is
disturbed
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9. 5.HYPERCOAGULABLE STATES
(THROMBOPHILIA) -Increased
risk develop venous thrombosis.
• Conditions may be hereditary
or acquired causes
• Hereditary factors
1. Deficiency of antithrombin III
2. Deficiency of protein C and S60
3. Mutation in factor V Leiden
4. Defects in fibrinolysis
5. Increased levels of
coagulations factors (II and VIII).
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12. continuation
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13. Morphologic Features
Grossly - various shapes, sizes and composition
• Arterial thrombi - white and mural
• venous thrombi - red and occlusive.
• Mixed white and red layers called lines of Zahn
• Red thrombi - are soft, red and gelatinous
• white thrombi - firm and pale.
Microscopically - . Red (venous) thrombi have more
abundant red cells
• leucocytes
• platelets entrapped in fibrin meshwork.
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14. FATE OF THROMBUS
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15. 2. ORGANISATION
• thrombus is not removed
• starts getting organised
• Phagocytic cells (neutrophils
and macrophages) appear
and begin to phagocytose
fibrin and cell debris
3. PROPAGATION
• thrombus enlarge in size
• due to more deposition
from the particular of
flowing blood
• ultimately cause
obstruction of some
important vessel.
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16. ORIGIN OF THROMBI AT DIFFERENT SITES
CARDIAC THROMBI
• Thrombi formed in chambers
of the heart & valve cusps
• more common in right atrium
,mitral and aortic valves
ARTERIAL THROMBI
Examples are
1. Aorta: aneurysms
2. Coronary arteries:
atherosclerosis
3.Renal artery: atherosclerosis
4. Cerebral artery: atherosclerosis
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