Normal Haemostasis Flashcards
What are blood coagulation?
haemostatic response to injury and assists in maintaining theintegrity of the vascular system
Where does the coagulation - fibrin clot - usually take place?
surface membrane of a monocyte or platelet
What is the first principle of haemostasis?
Require a normal number of normally functioning blood platelets, normally functioning vascular endothelium and functional coagulation cascade
What does the vascular endothelium do? (4)
produce prostaglandins and thromboxane ,
regulating tissue factor expression,
control angiogenesis, vascular permeability and vascular tone provide links with inflammatory pathways
Waterfall theory of coagulation cascades - what two bits of pathway did this have and what did they both produce?
Intrinsic and extrinsic pathway both producing factor 10
Waterfall theory - what starts the intrinsic pathway?
Contact with a surface which activates factor 12 with HMWK and Prekallikrein to make activated factor 12 a.
Waterfall theory - what does the activated pathway need?
Tissue factor and activated factor 7 to make activated factor 10 a from factor 10.
Waterfall cascade - How many pathways make factor 10 A
2 - extrinsic and intrinsic
Waterfall theory - how does the common pathway make thrombin using factor 10a?
Factor Xa as the enzyme, cleaves the substrate, factor II also known as “prothrombin” in the presence of a co-factor, factor Va, enabling the generationof thrombin.
Waterfall Theory - what does thrombin do after being produced by this cascade?
cleaves fibrinopeptides from fibrinogen to generate fibrin strands,
Waterfall theory - what happens to the fibrin strands after being cleaved from fibrinogen?
Cross-linked by factor 13a to become a fibrin clot
Why is the waterfall theory not accurate when reflecting homeostasis in clinical scenarios?
- Patients with factor XII deficiency do not bleed even though they should as the clotting cascade should not work.
- Patients with factor VII deficiency do bleed despite there being a functioning intrinsic pathway e.g. they shouldnt bleed.
- Patients with factors VIII and IXdeficiency have a severe haemorrhagic tendency, yet their extrinsic clotting pathway appears to befunctioning normally,
The new theory - what happens after vessel injury?
It will expose tissue factor
The new theory - after vessel injury what happens (this is called extrinsic tenase)?
With the tissue factor generated from the vessel injury (aka factor 3) and in the presence of ionised calcium and activated factor 7, factor 10 is converted into activate factor 10a.
New theory - What is the self dampening of extrinsic tenase know as and how does it work?
Tissue factor pathway inhibitor which makes a quarternary product with tissue factor, factor 7, 10 and 10aswitching of the pathway.
New theory - What does activated factor 10a do?
Catalyses the production of thrombin from prothrombin
New theory - How does activated factor 10a make thrombin from prothrombin and what does this require?
Through the macromolecular enzyme complex prothrombinase which required a negatively charged phospholipid surface membrane, ionised calcium and activated factor Va
New theory - What does the thrombin that is generated then go on to do?
Cleave fibrinopeptides from fibrinogen to form fibrin monomers. It also allows a short burst of platelet aggregation which enables initial blood clotting to take place.
New theory - what type of pathway does activated Xa and thrombin work in?
positive feedback loop
New Theory - what does the activated factor 10a and thrombin activate in their positive feedback loop?
activate factor 9
New theory - what does the activate factor 9a do in the presence of factor 8, ionised calcium and a phospholipid surface membrane do? And what is this pathway called?
cleave factor 10
intrinsic tenase
What is quicker the extrinsic tenase or the intrinsic tenase?
Extrinsic
What does intrinsic tenase make?
Factor 10a which helps maintain the thrombin and therefore the fibrin clot.
Why do people with factor 8 or 9 (aka haemophilia) bleed slower instead of just bleeding outright after an injury?
They don’t have factor 8 or 9 and therefore the intrinsic tenase does not produce factor 10. However, they are still able to produce factor 10a from the extrinsic tenase and therefore still form a clot. A few hours after an injury they may begin to bleed as the intrinsic tenase maintains the clot as it is not stable and so they may bleed later.
What is the treatment for haemophilia?
Replacement of factor 8 or 9
Where are factos 8 and 5 found?
In the phospholipid layer
What is the role of factor 8 and factor 5?
Find the circulating enzyme - serine protease and the substrate in the phospholipid surface membrane to help with catalytic activity.
What do both prothrombinate and intrinsic tenase have in common?
They are both vitamin K dependant serine protease.
What is the serine protease for intrinsic tenase?
factor 9a
what is the serine protease for prothrombinase
vitamin k dependant factor 10a
What is required for surface membrane enzyme complexes?
Calcium Ions and negatively charged phospholipid, with the appropriate ratio of phosphatidyl serine to phosphatidylcholine
When would the catalytic advantage be at its highest?
If the full combinations of the components of the complex are present and the appropraite temperature of 37 degrees
What domain is on the bottom of the catalytic domain that comes out of the phospholipid layers?
Gla domain
How do the two catalytic domains come together to generate factor 10a?
Factor 9 and factor 10 come together enabling the two catalytic domains to come near one another and therefore factor 10a can be generated
What would happen if there was mutations in factor 9, 10 or 8a?
The exact structural arrangement cannot take place, it can lead to reduced catalytic efficiency of the enzyme complex.
What is the molecular basis of haemophilia?
Reduced amount of factor 8 or genetic mutations in the factor 8 gene or defective factor 9 molecules
Which cause the failure of structural arrangements to bring the catalytic domains together. These therefore results in less factor 10a and then downstream reduced formation of thrombin.
What does emicizumab do?
This replaces factor 8a which usually holds the factor 10a and 9 catalytic domains together - this can help those suffering from haemophilia
What are the natural inhibitors that prevent the overactivity of the clotting cascade and what they effect?
Tissye factor inhibitor which regulates extrinsic tenase
Antithrombin which controls thrombin and factor 10a, 9a and 11a
Protein C pathway which inhibits factor 5 and factor 8a
How does the protein C pathway work?
Through thrombin modulin feedback loops
What are the laboratory measurements?
Prothrombin time (PT)
Activated partial thromboplastin time (APTT)
Fibrinogen
What does prothrombin time measure?
It is measured in seconds and reflects the extrinsic pathway and the common pathway
What does the activated partial thromboplastin time measure?
It is measured in seconds and measures the intrinsic and common pathways
What does fibrinogen measure?
Is measured in grammes per litre and reflects the functional activity of the fibrinogen protein.
Haemophilia A - what is this?
Its a rare x-linked recessive disorder in males.
What causes haemophilia A?
Deficiency of factor 8
The clinical severity of haemophilia A relies on what?
The levels of factor 8 you still have (the less you have the worst it is)
Symptoms of haemophilia A?
Large bruising after a traumatic bleed (this causes soft tissue bleeds)
Random and acute bleeding into joints.
Swelling
Joint disease - chronic arthropathy caused by repeated bleeding into joints.
What causes aquired haemophilia later in life?
Connective tissue problems, malignancy, after pregnancy and skin conditions
Where do you bleed in congenital haemophilia?
Joints, muscles and soft tissues
Where do you bleed in acquired haemophilia?
Almost everywhere including the retropharyngeal and retroperitoneal spaces, the brain and compartment syndrome (bleeding in between soft tissue planes and between muscle layers)
What is ecchymosis?
Extensive bruising in acquired haemophilia
What are the2 main categories of thrombosis?
Venous and arterial
What are types of venous thrombosis’?
DVT, pulmonary embolus or thrombosis in the cerebral, mesenteric, axillary, splachnic and splenic
What are types of arterial thrombosis’?
Myocardial infarction
CVA (stroke)
What are treatments for thrombosis’ and inhibitors of blood coagulation?
Anticoagulants
How are anticoagulants taken and what are some common ones?
Oral or parenteral
warfarin and heparin
How do anticoagulants work?
Act by inhibiting several points in the coagulant cascade.
What is the ideal characteristics of an anticoagulant?
Highly predictable anticoagulant profile
Few drug and food interactions
Oral administrations
No need for monitoring
Simple dosing
Reversal antidote
What are some natural anticoagulants?
Leech, tick, rhodniin
What direct anticoagulant drugs react directly on factor 10a?
Rivaroxaban, apixaban, edoxaban.
Where does dabigatran act on?
Thrombin directly
Why are direct anticoagulants not really used?
There wasnt many reversal agents however there has been some developed now
How does idarucizumab neutralise dabigatraon activity?
It binds free and thrombin bound dabigatran to neutralise its activity. It has immediate onset of action to immediately stop bleeding.
How does Andexanet alpha reverse the inhibition of factor 10a?
It is a recombinant human factor 10a decoy protein and can be used against apixaban and rivarox
What does DIC stand for?
disseminated intravascular coagulation
What is DIC?
An acquired syndrome of systemic intravascular activation of coagulation (thrombin explosion). This leads to fibrin being deposited in the circulation anf tissue ischemia and multi-organ failure.
How is severe bleeding induced in DIC?
Consumption of platelets and coagulation factors to generate thrombin to try and stop the DIC
How is vascular patency in DIC maintained?
Plasmin is generated in excess leading to fibrinogenolysis (break down of blood clots)
What does the aetiology of DIC include? (theres lots of these)
- Sepsis - gram positive or negative bacterial, fungal or parasitic infections
- Tumours - solid malignancies and haematological malignancy (acute promyelocytic leukaemia).
- Trauma - fat embolims, head injury, burns, lightning strikes
- Pancreatitis
- Obstetric - amniotic fluid embolism, abruptio placentae, pre-eclampsia
- Vascular - aortic aneurysm, kasaback meritt syndrome
- Toxic - recreational drugs, snake bugs, bats, caterpillar bites
- Transfusion of ABO incompatible cells.
How would you reverse DIC in a pregnancy?
Deliver the baby
What can be seen in some cases of DIC in the blood?
Red cells fragaments
In DIC what would the lab results show?
Prolonged prothrombin time
Prolonged activated partial thromboplastin time
Low fibrinogen
Raised D-dimer
Covid and venous thromboembolism - what caused this despite treatment with anticoagulants?
Overexpression of tissue factor
Endothelial dysfunction
Activation of complement system
Anctivation of contact pathway
Cytokine storm - inducing a pro-inflammatory state
What is the main fetures of covid coagulopathy?
Mild thrombocytopenia
High levels of D-dimer
Slight prolongation of Prothrombin time
Elevated factor 8
Elevated fibrinogen
In severe cases of covid coagulopathy what might you find?
Microvascular thrombosis
DVT and PE
Herapin resistance
