It is a vital process with the formation of a solid mass (thrombus) from blood element essentially platelets inside the cardio-vascular system during life.
Causes of thrombosis:
1. Damage of endothelial wall: as in atherosclerosis, direct pressure, trauma or inflammation of the arterial wall.
2. Slowing of the circulation:
• In leg veins as post-operative or after labor due to recumbency.
• Chronic venous congestion.
• Acute inflammation.
• Aneurysm and varicose veins.
3. Changes in blood constitutents:
• Increase in viscosity of blood as in dehydration and after operation.
• Decrease in heparin.
At first the platelets adhere to the site of endothelial damage, and then more platelets precipitate and accumulate in growing columns against the current of blood which appear as whitish lamina known as lines of Zhan. Stasis of blood occurs in between these lamina, in which fibrin threads are formed, entangling red and white blood cells.
Types of thrombi:
– Pale thrombus formed mainly of platelets.
– Mixed thrombus formed of different elements of blood.
Sites of thrombosis:
1- Thrombosis in veins: phlebothrombosis or thrombophlebitis.
2- Thrombosis in the arteries.
3- Thrombosis in the heart.
Fate of thrombus:
1- If small, it may be liquefied and dissolved.
2- Contraction with re-passing of blood again.
3- Detachment with embolic manifestation leading to infarction.
4- Infection with disintegration leading to septic emboli causing pyemia.
5- Organization or replacement with fibrous tissue with our without canalization.
6- Dystrophic calcification (phlebolith).