Flashcards in MOD 5.1 - Haemostasis and Thrombosis Deck (38):
What is haemostasis?
The process that stops bleeding
What are the depending factors of haemostasis?
- Vessel wall
- Coagulation System
- Fibrinolytic System
How do blood vessels contribute to haemostasis?
- 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)
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)
- Lines of Zahn (alternating lines of platelets mixed with fibrin)
- Lower cell content
Describe a venous thrombus (4)
- Deep red
- Higher cell content
What are the differences between a thrombus and a clot?
- Outside of blood vessels
- Pathological/not normal
- In blood vessels
What are the arterial effects of thrombosis? (2)
(depends on site and collateral circulation)
What are the venous effects of thrombosis (4)
- Ischaemia (tissue pressure due to oedema > arterial pressure)
What are the outcomes of thrombosis? (5)
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%?
- Amniotic Fluid
- Medical equipment
- Tumour cells
- Fat e.g. from a long bone fracture
What is the passage of an embolism from the heart?
- Via aorta
- Renal, mesenteric or any other arteries
What is the passage of an embolism from systemic veins?
- To lungs via the right heart
- Don't get stuck in large veins near heart
What is the passage of an embolism from atheromatous carotid arteries?
- To the brain (cause of a stroke)
What is the passage of an embolism from atheromatous abdominal arteries?
- To the arteries of the legs
What are the 4 types of pulmonary embolism?
- Massive PE (more than 60% reduction in blood flow = death)
- Major PE (medium vessels blocked = shortness of breath, coughing bloody sputum)
- Minor PE (small peripheral arteries blocked = no symptoms/minor shortness of breath
- Recurrent PE (pulmonary hypertension)
What are some of the causes of deep vein thrombosis? (4)
- Post partum
- Oral contraceptives
How are DVTs treated?
- Intravenous heparin (co factor for anti-thrombin 3)
- Oral Warfarin (interferes with vit K dependent clotting factors)
How is a cerebral embolism caused?
- Atrial fibrillation --> Stagnation of blood --> Thrombus
- Transient ischaemic attack/stroke if from left heart to brain
How is a Iatrogenic embolism caused?
Embolism due to medical treatment e.g. air from an injection
How is a nitrogen embolism caused?
Nitrogen bubble form in blood after rapid decompression e.g. the bends in divers
What is disseminated intravascular coagulation?
- Activation of coagulation mechanisms due to disease
- Small clots form throughout body and use up all clotting factors = abnormal coagulation
What is haemophilia?
- X-linked recessive disorder due to a nonsense point mutation
- Type A = deficiency in factor 8
- Type B = deficiency in factor 9
What can haemophilia cause?
- Haemorrhage into major joints
- Synovial hypertrophy