6) Haemostasis & Thrombosis Flashcards
(19 cards)
Define haemostasis
The body’s response to stop bleeding and blood loss
What factors affect haemostasis?
- Vessel wall
- platelets
- coagulation system
- fibrinolytic system
What is the function of platelets during thrombosis?
- adhere to the damaged vessel wall
- and to each other using ATP
- forms a platelet plug
Describe the factors which control coagulation
- balance between procoagulant and anticoagulant forces
- thrombin +vely feeds back on factors V, VIII and XI
- Inhibition by anti-thrombin 3, ⍺1 anti-trypsin, protein C (deficiencies lead to thrombophilia -excess thombosis)
- Fibrinolysis by plasmin (plasminogen -> plasmin by plasminogen activators)
Give an example of a thrombolytic agent, it’s clinical use and method of action
- Streptokinase
- coronary infarction by thrombus post-MI
- enzyme activates conversion of plasminogen -> plasmin
- plasmin causes fibrinolysis
Define thrombosis
Formation of a solid mass of blood within the circulatory system during life
What factors affect THROMBOSIS?
Virchow’s triad
Describe the differences in appearance in thrombi formed in arteries vs veins
Arterial thrombus:
- pale (less RBC:plasma), granular, lines of Zahn, lower cell content
Venous thrombus:
- deep red (high RBC:plasma), soft, gelatinous, higher cell content
Describe the difference in effects of thrombus in an artery compared to a vein
Artery:
- ischaemia, infarct (extent dependant on site and collateral circulation)
Vein:
- congestion, oedema, (ischaemia and infarct -when tissue pressure due to oedema > AP)
Describe the possible outcomes of thrombosis
- Lysis, (likely when small) complete dissolution and blood re-established
- Propagation, progressive spread of thrombus (distally in arteries and proximally in veins)
- Organisation, repair with ingrowth of fibroblasts and capillaries, lumen remain obstructed
- Recanalisation, blood flow re-established partially via formation of one or more channels
- Embolism
Define embolism and give some types
Blockage of a blood vessel by a solid, liquid or gas at a site distant to it’s origin
- Thrombo-emboli (most common)
- Air
- Amniotic
- Nitrogen (Divers Bends)
- Tumour cells
- Medical equipment
Describe the possible course (and hence blockage) of a thrombo-embolus originating from the leg
- pulmonary embolus (next point when veins begin to narrow)
- pass into circulation provided R>L shunt, and then:
- atheromatous carotid arteries leading to stroke
- atheromatous abdominal aorta, blocking arteries to leg
Describe the effects of different sized emboli entering the lungs
- MINOR, (small peripheral arteries blocked) asymptomatic or minor shortness of breath
- MAJOR, medium sized vessels blocked, blood in sputum
- MASSIVE (>60% reduction in blood flow), rapidly fatal Recurrent emboli can lead to pulmonary hypertension
List some possible causes of DVT and it’s treatment (explaining the action of the drugs quoted)
- immobility, post-op, post-patum, severe burns, cardiac failure, disseminated cancer (any time blood is hypercoaguable)
- INITIALLY with IV heparin (anti-coag, co-factor for anti-thrombin 3)
- LONG-TERM with warfarin (vit-K antagonist so prevents factor production at liver) slower to act -subcutaneous heparin, leg compression and TED stockings
DVT is a very common occurence during surgery, descibe possible prophylaxis for this
- subcutaneous heparin
- leg compression
- TED stockings
List some different types of emboli and their potential causes
- FAT, long bone fracture, adipose tissue laceration
- CEREBRAL, atrial fibrillation leading to stasis and thrombus formation, can enter brain and cause stroke/TIA
- IATROGENIC, due to treatment (excess air during injection)
- NITROGEN, bubbles form during rapid decompression causing ‘bends’
Describe Disseminated Intravascular Coagulation (DIC), it’s symptoms and possible treatment
- Pathological activation of coagulation mechanisms in response to a variety of diseases. (e.g infection, trauma, liver disease, obsteric complications)
- Small clots form throughout the body, disrupting normal coagulation as they use up all the clotting factors.
- Abnormal bleeding occurs from the skin.
- Treatment: Blood transfusion, Anti coagulants
What is haemophilia, the types, possible symptoms and treatments
X-R mutation leading to deficiency in a clotting factor, unable to clot
Type A (Factor VIII), type B (Factor IX)
- Haemorrhage into major joints, synovial hypertrophy
- Muscle bleeding causes pressure and necrosis of nerves (painful)
- Can haemorrhage into retroperitoneum / urinary tract
Treat with self-administered factor replacement therapy
What is Thrombocytopenia, possible causes, it’s symptoms and treatment
- Platelet count is below the reference range
- Failure of platelet production, increase in platelet destruction, sequestering of platelets
- Usually accompanied by a bone marrow dysfunction, E.g. leukaemia, anaemia
- Lobar Pneumonia
- If it is due to sequestering, cause may be DIC
