Haemostasis Flashcards
What does blood do?
flows within the vascular system, transporting oxygen, nutrients and hormonal information around the body and removing metabolic waste
Why is a balance in haemostasis important?
- coagulation
- prevent generalised thrombosis
- start the process of fibrinolysis
What is coagulation?
stimulation of blood clotting processes following injury, in which blood changes from its liquid state
What is thrombosis?
excessive or generalised blood clotting
What is fibrinolysis?
the breakdown of the clot as part of the process of healing
What does haemostasis result from?
- Contraction of blood vessels (vasoconstriction)
- Formation of an unstable platelet plug at the site of the vessel wall damage (primary haemostasis)
- Formation of a stable fibrin clot (secondary haemostasis/coagulation)
What is vasoconstriction?
Contraction of blood vessels
What is primary haemostasis?
Formation of an unstable platelet plug at the site of the vessel wall damage
What is secondary haemostasis/coagulation?
Formation of a stable fibrin clot
What is the sequence of haemostasis?
- vasoconstriction
- primary haemostasis
- secondary haemostasis
- fibrinolysis
What are platelets?
discoid, non-nucleated, granule-containing cells that are derived from myeloid stem cells
Where are platelets formed and what from?
bone marrow by the fragmentation of megakaryocyte cytoplasm
What is the circulating lifespan of platelets?
around 10 days
What is important in the platelets interaction?
The plasma membrane contains glycoproteins (GPs)
What happens after injury to the vessel wall?
platelets stick to the damaged endothelium
How do platelets stick to the damaged endothelium?
either directly to collagen via the platelet GPIa receptor
or indirectly via von Willebrand factor (VWF), which binds to the platelet GPIb receptor
What happens after the adhesion of platelets?
become activated and change their shape from a disc to a more rounded form with spicules to encourage platelet-platelet interaction
What happenes after platelets are activated?
They release of the contents of their storage granules
What are the 2 types of granules in platelets?
a-granules
dense granules
How are the contents of platelet granules released?
The platelet membrane is invaginated to form a surface-connected cannalicular system through which they are released
What are the components of the granules in platelets?
ADP, fibrinogen and von Willebrand factor
What do platelets produce when they are stimulated?
prostaglandin thromboxane A2 from arachidonic acid that is derived from the cell membrane
What is the role of thromboxane A2?
Has a role in platelet aggregation
it is a vasoconstrictor and is especially important during tissue injury and inflammation
What is thromboxane A2 synthesised from?
Arachidonic acid –(ASA + Cyclo-oxygenase)–> Cyclic endoperoxides
in platelets:
Cyclic endoperoxides–(thromboxane synthetase)–> thromboxane A2 —-> plt aggreg.