MOD 5.1 - Haemostasis and Thrombosis Flashcards
What is haemostasis?
The process that stops bleeding
What are the depending factors of haemostasis?
- Vessel wall
- Platelets
- Coagulation System
- Fibrinolytic System
How do blood vessels contribute to haemostasis?
- Constrict
- Decreases blood volume so limits loss
How do platelets contribute to haemostasis?
- Stick to each other and to the walls of the vessels
- Forms a platelet plug
How does the coagulation system contribute to haemostasis?
- Inactive components become activated in a cascade
- Thrombin converts fibrinogen to fibrin for clotting
What is fibrinolysis?
- Breakdown of fibrin i.e. clots
- Done by plasmin
How is the coagulation system regulated?
- Thrombin positively feedbacks on factors 5, 8 and 11 (so increased Thrombin = increase in specific factors)
- Thrombin is inhibited by:
- Antithrombin 3
- Alpha 1 anti trypsin
- Protein C/S
What is used in fibrinolytic therapy and what does this achieve?
When in fibrinolytic therapy used?
- Streptokinase, activates plasminogen to be convertedto plasmin
- Serious cases e.g. coronary artery occlusion
What do hereditary deficiencies in antithrombin 3 or protein C/S cause?
- Thrombophilia (blood is more likely to form clots which increases chance of a DVT)
- Thrombosis
What is thrombosis?
The formation of a solid mass of blood within the circulatory system during life
What are the predisposing factors to thrombosis? (Virchow’s Triad)
1) Changes in blood flow (stagnation/turbulence)
2) Changes in blood vessel walls (trauma, atheroma, inflammation)
3) Changes in blood components (Post op, post partum, smoking = increase in coagulation factors)
Describe an arterial thrombus (4)
- Pale
- Granular
- Lines of Zahn (alternating lines of platelets mixed with fibrin)
- Lower cell content
Describe a venous thrombus (4)
- Deep red
- Soft
- Gelatinous
- Higher cell content
What are the differences between a thrombus and a clot?
Clot =
- Physiological/normal
- Outside of blood vessels
Thrombus =
- Pathological/not normal
- In blood vessels
What are the arterial effects of thrombosis? (2)
- Ischaemia
- Infarction
(depends on site and collateral circulation)
What are the venous effects of thrombosis (4)
- Congestion
- Oedema
- Ischaemia (tissue pressure due to oedema > arterial pressure)
- Infarction
What are the outcomes of thrombosis? (5)
- Resolution/lysis
- Recanalisation
- Embolism
- Organisation
- Propagation
Describe resolution/lysis of a thrombus
- Complete breakdown of the thrombus
- Re-establishment of blood flow
Describe recanalisation of a thrombus
- Channels form through the thrombus
- Results in partial re-establishment of flow
Describe embolism of a thrombus
- Part of the thrombus breaks off
- Blocks a different site
Describe organisation of a thrombus
- Reparative process
- Ingrowth of fibroblasts and capillaries
- Still obstructs lumen
Describe propagation of a thrombus
- Thrombus gets bigger in direction of blood flow
- Arteries = Distal
- Veins = Proximal
What is an embolism?
The blockage of a blood vessel by a solid, liquid or gas at a site that is distant from its origin
If 90% of emboli are thrombo-emboli, what makes up the other 10%?
- Air
- Nitrogen
- Amniotic Fluid
- Medical equipment
- Tumour cells
- Fat e.g. from a long bone fracture
