Blood Clotting Pathways Flashcards
What is haemostasis?
The arrest/halt of blood flow
How can this occur clinically?
After everyday trauma
e.g. injections, surgical incisions, tooth extractions etc.
What are the 3 major steps of haemostasis?
- Vascular spasm
- Formation of a platelet plug
- Blood coagulation (clotting)
Why must haemostasis be appropriately controlled?
To avoid inappropriate clot formation. Clots must be eventually degraded as they are only a temporary solution.
What happens during a vascular spasm?
VASOCONSTRICTION (contraction) of blood vessels occurs after injury:
- Muscle cells contract
- Constriction reduces blood flow, limits blood loss
- Opposing endothelial surfaces are pressed together and adhere on contact.
What is the process of a vascular spasm mediated by?
This process is mediated by the platelet-derived products serotonin and thromboxane A2 (TXA2).
What does normal endothelium produce?
Normal endothelium produces vasodilators and inhibitors of platelet aggregation to keep vessels open.
What are platelets also known as?
Thrombocytes
What are platelets?
Platelets are small fragments derived from megakaryocytes (bone marrow cells)
What do platelets contain?
They contain:
- megakaryocyte cytoplasm
- intracellular granules
- other organelles for generating energy
- high concentrations of actin & myosin
What do the high concentrations of actin & myosin allow the platelets to do?
What else can platelets do?
These high concentrations allow platelets to contract
Platelets can also release secretory products
Under normal conditions, what do platelets not stick to?
Blood vessel endothelium.
What 4 chemical factors can activate platelets?
- ADP
- Collagen
- Thrombin
- PAF
What is PAF?
A phospholipid (not a protein)
What happens to the shape of platelets when they become activated?
What does this change in shape facilitate?
Disc shape to sphere shape with extended pseudopodia.
This change in shape facilitates aggregation and coagulant activity.
As well as changing shape, what 4 other effects does activation have on platelets?
- They release compounds involved in homeostasis (e.g. ADP, serotonin, fibronectin and von Willebrand Factor (vWF))
- They aggregate
- They adhere/stick to the vessel wall
- They synthesise thromboxane A2 (TXA2)
What is thromboxane A2 (TXA2)?
A mediator of platelet activation and vasoconstriction.
What is platelet activation followed by?
Their ADHESION to the vessel wall at the site of injury.
What do the platelets do at the site of injury?
What does the product form?
The platelets AGGREGATE and build up an occlusive PLATELET MASS.
This mass forms the PRIMARY HAEMOSTATIC PLUG.
When vasoconstriction eases, what may happen to the plug?
Plug may be washed away by local blood flow.
What must the plug be stabilised by?
The plug must be stabilised by FIBRIN
What are the two main steps of the formation of the Platelet Plug?
- Platelets aggregate to form a primary plug
2. Platelets release chemicals which enhance blood coagulation.
When looking at platelet disorders and platelet-related bleeding disorders, what is the most common defect?
The most common defect is von Willebrand disease.
What is von Willebrand disease?
A group of autosomal diseases affecting vWF
