Haemostasis and Clot Lysis Flashcards
What is haemostatis ?
Prevention of blood loss
What are the three phases of haemostasis?
- Vascular spasms
- Platelet plug formation
- Coagulation
What do vascular spams do?
Cause immediate vasoconstriction in response to injury which limits the blood flow therefore limits blood loss
What will damage to endothelium release and what does this cause?
Endothelin
Causes vasoconstriction
How is damage to the vascular smooth muscle mediated ?
Contraction of the smooth muscle cells
How are nervous reflexes mediated ?
Sympathetic NS
Sensory nerve fibres that detect pain
What causes vasoconstriction of the vascular smooth muscle during vascular spasms?
- Nervous reflexes
- Myogenic contraction
- Factors from damaged tissue and activated platelets e.g. endothelin, thromboxane A2, serotonin (5-HT)
What is exposed when a blood vessel wall is damaged?
~Collagen
~Tissue factor
What happens when collagen is exposed to blood?
— Platelets begin to adhere to the exposed collagen, activate and release chemicals called platelet factors
— Platelets aggregate into a loose platelet plug
How are platelets actives?
By contact with:
- Von Willebrand factor
- Thrombin
- Collagen
- A negatively charged surface
What produces von Willebrand factor and when is this production highest?
Endothelial cells
Damaged endothelial cells
Why is blood not stored in glass?
The platelets would become activated due to the negatively charged surface of the glass and would cause the blood to begin to clot
What do the spines of activated platelets allow them to do?
- To stick to each other
2. To stick to the damaged surface of the blood vessel
What are the normal features of the endothelial surface of a vessel wall?
- Smooth
- Has a glycocalyx
- Releases prostacyclin and NO
- Contains thromobomodulin
What forms a glycocalyx and what does it do?
Made up of mucopolysaccharides
It physically repels the platelets and clotting factors
Why do platelets not normally stick to the vessel wall?
As it has an endothelial surface
What do prostacyclin, NO and thrombomodulin do?
Prevent platelet activation
What do activated platelets release ?
- ADP
- Thromboxane A2
- Serotonin
What type of feedback is platelet plug formation an example of?
Positive feedback
What initiates the clotting cascade ?
Tissue factor
What activates clotting factor XII and where are they activated ?
Platelets
Liver
When do the extrinsic and intrinsic pathways finish ?
Clotting factor X
Does clotting occur faster in the intrinsic of extrinsic pathway?
Extrinsic
What is factor X critical in?
The conversion of prothrombin (II) to thrombin (II) through complexing with prothrombin activator
