Flashcards in MOD S6 - Haemostasis and Thrombosis Deck (36)
What is haemostasis?
The body's response to stop bleeding and loss of blood
What does successful haemostasis depend on?
How do blood vessels allow successful haemostasis?
They constrict to limit blood loss
How do platelets allow successful haemostasis?
Platelets adhere to the damaged vessel wall and to each other
This forms a platelet plug
How does the coagulation system allow successful haemostasis?
Enzyme cascade (in a series of inactive components, one active component can activate the rest)
Tightly controlled (because 1ml of blood can activate enough thrombin to convert all the fibrinogen in the body into fibrin)
Balance of pro coagulant and anticoagulant forces
How is the coagulation system regulated?
Thrombin positively feeds back on factors V, VIII and XI
Thrombin inhibitors: alpha 1 antitrypsin, anti thrombin III, alpha 2 macroglobulin, protein c/s
What genetic factors can interfere with coagulation?
Deficiencies in anti thrombin III or protein C/S cause thrombophilia and thrombosis
Breakdown of fibrin by plasmin
Plasminogen is converted to plasmin by activators eg streptokinase
Fibrinolytic therapy widely used (commonly know as clot busting drugs) as a drastic treatment when thrombi block important blood vessels
The formation of a solid mass of blood in the circulatory system DURING LIFE
What is Virchow's Triad?
Changes in blood flow - stagnation, turbulence
Changes in vessel wall - atheroma, injury, inflammation
Changes in blood components - smokers, pregnancy
What is the difference between thrombi formed in veins and arteries?
Colour - arterial thrombi are pale but venous are a deep red
Consistency - arterial thrombi are granular but venous are soft
Structure - arterial thrombi have lines of Zahnm but venous are gelatinous
Cell content - arterial thrombi have a lower cell content and venous have a higher cell content
What are the effects of thrombi in arterial circulation?
Depends of site and collateral circulation
What are the effects of thrombi in venous circulation?
+If pressure of oedemaIschaemia
What are the possible outcomes of thrombosis?
Define lysis (as an outcome of a thrombus)
Complete dissolution of thrombus
Fibrinolytic system active
Blood flow reestablished
Most likely when thrombi are small
Define propagation (as an outcome of a thrombus)
Progressive spread of thrombus
In veins, progresses proximally
In arteries, progresses distally
Describe organisation (as an outcome of a thrombus)
Involves ingrowth of fibroblasts and capillaries
Lumen remains obstructed
Describe recanalastion (as an outcome of a thrombus)
Blood flow reestablished (usually incompletely)
One or more channels form through organising thrombus
Describe embolism (as an outcome of a thrombus)
Part of the clot breaks off and travels via bloodstream to a distant site
If coronary artery, can cause MI (myocardial infarction)
If lungs, can cause PE (pulmonary embolism)
What is an embolism?
Blockage of a blood vessel by solid, liquid or gas at a site distant from the site of origin
What type of emboli can you have?
Thrombo-emboli are the most common
Where is a thromboembolism originating from a systemic vein likely to cause problems?
Aka pulmonary embolism
Where is a thromboembolism originating from the heart likely to cause problems?
Pass via the aorta to renal, mesenteric and other arteries
Where is a thromboembolism originating from a carotid artery likely to cause problems?
In the brain
Causes a stroke
Where is a thromboembolism originating from the abdominal aorta likely to cause problems?
In the legs
Describe the various severities of PE
Massive PE - >60% reduction in blood flow, rapidly fatal
Major PE - medium sized vessel blockage. Shortness of breath, cough, bloody sputum
Minor PE - small, periphery vessels blocked. Shortness of breath or asymptomatic
Recurrent PEs - cause pulmonary hypertension
What are some risk factors for a DVT?
Extended bed rest/immobility
Pregnancy & post-partum
How are DVTs treated?
IV heparin (anticoagulant and anti thrombin III cofactor)
Oral warfarin (interferes with vitamin k dependent clotting factors, slow effect)
Describe fat emboli
>Can be caused by:
-Breakage of a long bone
-Laceration of adipose tissue
-Shortness of breath