Haemostasis Flashcards
What is haemostasis?
The stopping of blood loss from damaged vessels.
What are the properties of platelets under normal circumstances and where are the found?
They are non-adhesive and are found circulating freely in the blood.
During vessel wall injury, what happens to the circulating platelets?
They become ‘sticky’ and aggregate.
What is thrombosis? What conditions can it lead to?
The formation of a blood clot inside a vessel. It can lead to MI (heart) or stroke (brain).
Explain why haemostasis is described as an ‘active’ process?
Because even arrest processes are occurring to STOP inappropriate thromboses (clot formations).
What is another name for platelets?
Thrombocytes.
Which X2 layers of the blood vessels are involved in the vascular control of platelets function (activating/mediating them)?
The endothelial cells of the tunica intima answer the smooth muscle cells of the tunica media.
What does NO stand for? Where is it released from and what does it do?
Nitrous oxide
It is released from the endothelial cells and has a NEGATIVE effect on platelet activation and vasculature smooth muscle cell contraction.
What’s does PGI2 stand for? Where is it released from and what does it do?
Prostaglandin I2
Or
Prostacyclin
It is released from the endothelial cells and has a NEGATIVE effect on platelet activation and vasculature smooth muscle cell contraction.
What does EDHF stand for? Where is it released from and what does it do?
Endothelium derived hyperpolarising factor.
It is released from the endothelial cells and has a NEGATIVE effect on vasculature smooth muscle cell contraction.
What does ET-1 stand for? Where is it released from and what does it do?
Endothelin 1
As it’s name suggests it is released from the endothelial cells and has a POSITIVE effect on vasculature smooth muscle contraction.
What does TXA2 stand for? Where is it released from and what does it do?
Thromboxane A2
As it’s name suggests it is released from ACTIVATED platelets (thrombocytes) and has a POSITIVE effect on vasculature smooth muscle contraction. It utilises the cycle-oxygenase 1 (COX-1) enzyme to do this.
What is the difference between primary and secondary haemostasis?
Primary = formation of a “platelet plug” at the endothelial wall
Secondary = activation of the clotting cascade and clot stabilisation via fibrin
Describe primary haemostasis.
1) blood vessels are damaged
2) platelets are exposed to collagen in the ECM causing them to activate and adhere. This is strengthened by Von Willebrand Factor (vWF) (usually circulating found to FVIII) binding to the collagen.
3) the activated platelets release TXA2 which stimulated vascular vasoconstriction.
4) a soft platelet plug is formed
What are the phases of the clotting cascade?
The extrinsic pathway (initiation) and the intrinsic pathway (amplification and propagation) both leading to a final common pathway.
What is another name for the intrinsic pathway of the clotting cascade?
Amplification and propagation.
What is another name for the extrinsic pathway of the clotting cascade?
Initiation
What activates the initiation pathway and what type of structure is this?
Tissue factor (Tf) - a transmembrane receptor.
Where is TF usually found?
Cells of the vasculature not usually in contact with flowing blood. It is EXTRINSIC to the system hence the old initiation pathway name.
What does the nomenclature FVIa mean?
F = factor VI = Roman numeral of the factor (6 in this example) a = activated
Which clotting factor does TF bind to when vessel damage occurs, and where is this usually found?
TF binds to FVII (usually found circulating in the blood) to form a TF:FVIIa complex as FVII is activated…
TF + FVII ——-> TF:FVIIa complex