Haemostasis Basics Flashcards
Haemostasis
The cessation of bleeding at a vascular injury site via the formation of a thrombus
Platelet Plug
Primary haemostasis
Circulating platelets form physical plug
Adhere to injury site + each other
Stop leak
Fibrin Clot
Secondary haemostasis
Assembly + activation of series of coagulation factor proteases
Cause thrombin production
Thrombin
Produces fibrin monomers
Can cross link together to form stabilised protein meshwork around plug
Platelets derivation
Megakaryocyte
1 megakaryocyte= over 1000 platelets
Platelets structure
no nucleus
1-4microm
Platelet circulation time
8.5-10 days
Platelet half life
4 days
Platelet production regulation
Thrombopoietin
Platelet level normal
150-400 x10(9) per litre
Thrombocytopenia
Platelets below 150x10(9) per litre
Thrombocytosis
Platelet above 400x10(9) per litre
Platelet adhesion prevention
NO and PGI2 (prostacyclin) release
What happens when endothelium exposed
NO production stops
Collagen under endothelium exposed
VWF
Protein in blood
Binds to exposed collagen
Receptor which helps bind platelets to VWF
Platelet GP1b receptor
Platelet GP2b/3a receptor
Expressed by adherent platelets
Binds to fibrinogen
Fibrinogen binds to more platelets to form meshwork
Platelet aggregation pathway
Endothelium exposed NO production stops Collagen under endothelium exposed VWF binds to collagen Platelets bind to VWF via GP1b receptors Platelets express GP2b/3a receptor Receptor binds to fibrinogen Meshwork formed
Bound platelet changes
Become spiky + change shape
Release ADP, TXA2 and 5HT
ADP + TAX2 effect
Attract more platelets to the site
Aggregate to form platelet plug
5HT effect
Acts on local smooth muscle
Vasoconstriction
Bleeding time test
Normally stops 1-9mins
Children 1-13 mins
F>M
Plug spread prevention
Healthy endothelium next to damaged site releases NO
Extrinsic pathway
Triggers coagulation after vessel injury
