Haemostasis Flashcards
What is haemostasis?
The stopping of haemorrhage
What does haemostasis involve?
Blood clotting
Vasoconstriction platelet plug formation
Clotting process
Blood in a normal vessel becomes a solid mass when it connected with connective tissue
What are the only cells that can be in contact with blood and not clot it?
White blood cells
Epithelium
Unactivated platelets
Red blood cells
Three steps of haemostatsis
The severed artery contracts enough to decrease the pressure down stream,
A primary haemostasis plug forms at the hole in the vessel
The secondary¥ haemostat is plug forms as fibrin filaments stabilise the platelet plug into a blood clot
What are platelets activated by?
Collagen surfaces
ADP- released by other activated platelets and damaged RBCs
Thromboxane A2- a powerful platelet aggregator
Thrombin
What do platelets do when they are activated?
Stick to exposed basement membrane or collagen
Aggregate with other platelets
Swell and change shape to sticky spheres
Secrete granules to help the platelet plug grow
2 pathways of clotting
Intrinsic- it contains factors which are all contained in the blood
Extrinsic - needs a tissue factor which is present outside of the blood
What does the vascular wall do in haemostasis?
Arterial media contractswhen artery is damaged and subendothelium traps platelets
Factors tha oppose clotting
Dilution of clotting factors by blood flow and anticoagulants
Fibrinolysis
Once the hole in the wall has been repaired the blood clot is dissolved by fibrinolysis - macrophages recognise it and break it down
haemophilia A
It is a deficiency of factor VIII. It is X linked recessive
Haemophilia B
It is factor IX deficiency but is also x linked recessive
Von willebrand disease
Can vary in severity from being a symptomatic to being severe bleeding disorder. Caused by a deficiency in Von willebrand factor
What is a normal platelet count?
150-400 x10^9/ L
