Haem 2S: Haemostasis and Thrombosis Flashcards
What are the procoagulation factors?
Primary haemostasis
- Platelets
- Endothelium
- vWF
Coagulation cascade
What are the anticoagulation factors?
Natural inhibitors of thrombosis
- Anti-thrombin
- Protein C / Protein S
- Tissue Factor Pathway Inhibitor (TFPI)
Fibrinolysis
Which 3 responses does Vessel injury stimulate?
- Vasoconstriction - in order to minimise blood loss
- Platelet activation - forms the primary haemostatic plug
- Activation of the coagulation cascade
What are the Components of blood clot formation?
- Vascular endothelium
- Platelets
- Coagulation proteins
- White blood cells
How is the Vascular Endothelium invovled in coagulation?
- The endothelium acts as a barrier which prevent exposure of pro-coagulant subendothelial structures
- Endothelial damage exposes these pro-coagulant substances which then triggers a haemostatic response
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Endothelial cells also produce:
- Prostaglandins (PGI2)
- vWD
- Plasminogen activators (activate fibrinolysis)
- Thrombomodulin
- The exposure of subendothelial pro-coagulant factors leads to platelet aggregation at the site of damage
Where are platelets produced?
- Produced in the bone marrow and originate from megakaryocytes
- Each megakaryocyte can produce up to 4000 platelets
- Platelets have a life span of 10 days (anti-platelet drugs halt platelet activity for 10 days)
- Clinical relevance: someone on aspirin needs surgery –> stop aspirin 7-10 days before surgery
- The production of platelets is regulated by a range of thrombopoietic factors (e.g. thrombopoietin, IL-6, IL-12)
- These can be given therapeutically to stimulate platelet production
What is the structure of platelets?
- Glycoproteins = cell surface proteins via which platelets can interact with the endothelium, vWF and other platelets
- Dense granules contain energy stores (in the form of ATP and ADP)
- The presence of an ‘open canalicular system’ and ‘microtubules and actomyosin’ means that platelets are capable of massively expanding their surface area
How do platelets migrate and adhere to the vascular endothelium?
- Two methods of adhesion:
- DIRECTLY – GlpIa
- INDIRECTLY – vWF via GlpIb
- Adhesion of platelets to exposed structures à release of ADP and thromboxane A2 à platelet aggregation
- Platelets attach to each other via GlpIIb/IIIa
- I.E. the fibrinogen receptor
What is the Arachidonic Acid Pathway?
- Aspirin will irreversibly inhibit COX
- NSAIDs are different from aspirin because they reversibly block COX
Which other receptors are important for platelet adhesion to the vascular endothelium?
- ADP receptors are also very important for platelet aggregation
- Examples of inhibitors: clopidogrel, ticagrelor
What are the roles of Coagulation Proteins, White Blood Cells in coagulation?
- A fibrin mesh needs to be generated to reinforce the clot
- Intrinsic pathway = in-vitro during clotting studies
- Extrinsic pathway = the body
- Factor Xa is the rate-limiting step for fibrin formation
- Pathway triggered by trace amounts of thrombin (which is formed following the activation of the platelet plug)
What are the effects of thrombin?
- Activates fibrinogen
- Activates platelets
- Activates pro-cofactors (Factor 5 and Factor 8)
- Activates zymogens (Factor 7, 11 and 13)
What do the following link up to form?
- fibrinogen
- platelets
- pro-cofactors (Factor 5 and Factor 8)
- zymogens (Factor 7, 11 and 13)
- These all link together to form a prothrombinase complex à activation of prothrombin to thrombin
What is the most important step of the coagulation cascade?
- KEY POINT: the MOST IMPORTANT step of the coagulation cascade is the generation of THROMBIN
What is the final step of the coagulation cascade?
- Thrombin will catalyse the breakdown of fibrinogen to FIBRIN which is the final step in the coagulation cascade
What are the phases of clotting?
- Factor 10a binds Factor 5a = 1st step of the coagulation cascade
- Factor V Leiden will not be able to bind Factor 5a to Factor 10a
- Activated platelet → thrombin burst (convert fibrinogen → fibrin)
How does the rate of prothrombin activation change?
What does PT and APTT refer to?
PT = INR = extrinsic pathway
APTT = intrinsic pathway
Summarise the intrinsic extrinsic and common pathways of the coagulation cascade
Which coagulation factors are Vitamin K-dependent? Where are these produced?
Vitamin K-dependent factors = 2, 7, 9, 10 (produced in the liver)
Why is Vitamin K necessary in for the coagulation cascade?
Biological activation =
vitamin K is required as a co-enzyme for the gamma-carboxylation of the clotting factors
Why might Abx reduce Vitamin K intake?
Bacteria help produce vitamin K → taking antibiotics can harm gut flora → reduce your vitamin K absorption
Why might Abx reduce Vitamin K intake?
Bacteria help produce vitamin K → taking antibiotics can harm gut flora → reduce your vitamin K absorption
Why might Abx reduce Vitamin K intake?
Bacteria help produce vitamin K → taking antibiotics can harm gut flora → reduce your vitamin K absorption
Why might Abx reduce Vitamin K intake?
Bacteria help produce vitamin K → taking antibiotics can harm gut flora → reduce your vitamin K absorption
Why is bile necessary to absorb vitamin K?
Vitamin K is fat soluble so need bile to absorb vitamin K (i.e. bile duct obstruction → deficiency)
Why might Abx reduce Vitamin K intake?
Bacteria help produce vitamin K → taking antibiotics can harm gut flora → reduce your vitamin K absorption
Why might a bile duct obstruction reduce vitamin K absorption?
Vitamin K is fat soluble so need bile to absorb vitamin K (i.e. bile duct obstruction → deficiency)
Why might Abx reduce Vitamin K intake?
Bacteria help produce vitamin K → taking antibiotics can harm gut flora → reduce your vitamin K absorption
Why is bile necessary to absorb vitamin K?
Vitamin K is fat soluble so need bile to absorb vitamin K (i.e. bile duct obstruction → deficiency)
Why might Abx reduce Vitamin K intake?
Bacteria help produce vitamin K → taking antibiotics can harm gut flora → reduce your vitamin K absorption
Why might Abx reduce Vitamin K intake?
Bacteria help produce vitamin K → taking antibiotics can harm gut flora → reduce your vitamin K absorption
Why is bile necessary to absorb vitamin K?
Vitamin K is fat soluble so need bile to absorb vitamin K (i.e. bile duct obstruction → deficiency)
What does the term fibrinolysis mean?
Blood Clot Removal
Where is Tissue plasminogen activator (tPA) produced? What is its role?
Tissue plasminogen activator (tPA) is produced by the endothelium (converts plasminogen to plasmin)
Which conditions is tPA sometimes used to treat?
tPA is sometimes given in stroke, MI and peripheral vascular disease
What else can activate plasminogen to plasmin?
Urokinase
What can inhibit tPA and urokinase?
tPA and urokinase are inhibited by plasminogen activator inhibitor 1 & 2
What is plasmin inhibited by?
Plasmin is inhibited by:
- Alpha-2 antiplasmin
- Alpha-2 macroglobulin
What is an important inhibitor of fibrin breakdown?
Thrombin-activatable fibrinolysis inhibitor (TAFI) is an important inhibitor of fibrin breakdown
Summarise the process of fibrinolysis
RED = inhibitory effect BLUE = stimulatory effect
Name the Physiological anticoagulants
- Antithrombins (ATs)
- Protein C and S
- Tissue factor pathway inhibitor (TFPI)