Coagulation Pathways
- In health, coagulation proteins, platelets and endothelium
limit local bleeding
- When injured, platelets stop local bleeding on endothelium.
Coagulation cascade follows.
o Adverse in this either causes prolonged bleeding or
thrombosis
Virchow’s Triad
- 3 predisposing features to injury:
o Injury to vessel (endothelial) wall
o Altered blood flow e.g. from atheroma
o Abnormal coagulability – can be caused
by certain drugs e.g warfarin and aspirin
Normal Haemostasis
- Platelets maintain the vascular integrity (normal
haemostasis)
- Platelets are non-nucleated fragments of granular cytoplasm
- Approx 150 to 400 × 109 /litre
- Are granulated – α- granules are the most abundant – contain lots of peptides and proteins
inc. vWF
- Are very contractile and adhesive
- Function: to maintain the vascular integrity if the endothelium breaks
- Primary haemostatic plug:
o If endothelium breaks there becomes an exposure to subendothelial structures in
the vessel to platelets
o This causes rapid adhesion of platelets to exposed area
o Leading to aggregation of platelets to each other
Platelet adhesion
- Breached endothelium leads to exposure
to the subendothelium and collagen to
the platelets
- Causes activation of platelets
- They change shape and produce
pseudopods (projections) which adhere
to the damaged area via von Willebrand
factor and glycoprotein receptor sites
- von Willebrand factor is a multimeric (a
protein that has multiple polypeptide chains)
o is synthesised by endothelial cells and megakaryocytes
o also associates with factor 8
- In health, coagulation proteins, platelets and endothelium
limit local bleeding
- When injured, platelets stop local bleeding on endothelium.
Coagulation cascade follows.
o Adverse in this either causes prolonged bleeding or
thrombosis
Virchow’s Triad
- 3 predisposing features to injury:
o Injury to vessel (endothelial) wall
o Altered blood flow e.g. from atheroma
o Abnormal coagulability – can be caused
by certain drugs e.g warfarin and aspirin
Normal Haemostasis
- Platelets maintain the vascular integrity (normal
haemostasis)
- Platelets are non-nucleated fragments of granular cytoplasm
- Approx 150 to 400 × 109 /litre
- Are granulated – α- granules are the most abundant – contain lots of peptides and proteins
inc. vWF
- Are very contractile and adhesive
- Function: to maintain the vascular integrity if the endothelium breaks
- Primary haemostatic plug:
o If endothelium breaks there becomes an exposure to subendothelial structures in
the vessel to platelets
o This causes rapid adhesion of platelets to exposed area
o Leading to aggregation of platelets to each other
Platelet adhesion
- Breached endothelium leads to exposure
to the subendothelium and collagen to
the platelets
- Causes activation of platelets
- They change shape and produce
pseudopods (projections) which adhere
to the damaged area via von Willebrand
factor and glycoprotein receptor sites
- von Willebrand factor is a multimeric (a
protein that has multiple polypeptide chains)
o is synthesised by endothelial cells and megakaryocytes
o also associates with factor 8
