Haemostasis Flashcards
What is haemostasis?
Cessation of bleeding whilst maintaining vascular patency
Define primary haemostasis
Formation of platelet plug
Define secondary haemostasis
Formation of fibrin clot
List components of normal haemostatic system
Primary haemostasis
Secondary haemostasis
Fibrinolysis
Anticoagulation
How are platelets formed?
Formed in bone marrow by budding from megakaryocytes
Describe the appearance of platelets on blood film
Small anucleate discs
List, in order, the stages of platelet plug formation
Endothelial DAMAGE exposes collagen
Release of vWF + proteins with platelets receptors
Platelet ADHESION at site of injury
SECRETION of proteins that attract more platelets
Platelet AGGREGATION at site of injury
List causes of failure of platelet plug formation
Vascular Less platelets (thrombocytopaenia) Reduced platelet function Von Willebrand factor deficiency
List consequences of failure of platelet plug formation
Spontaneous bruising and purpura
Mucosal bleeding (epistaxis, GI, conjunctival, menorrhagia)
Intracranial haemorrhage
Retinal haemorrhage
What is purpura?
Non-blanching red or purple discolored spots on the skin, typically of the lower limbs
What is the main screening test/investigation for primary haemostasis?
Platelet count
List, in order, the stages of fibrin clot formation
INITIATION: TF/VIIa activate V/XA
V/Xa facilitate the formation of prothrombin (II)
Prothrombin is converted into thrombin (IIa)
Thrombin activates fibrinogen (I)
PROPAGATION: Fibrinogen is converted into fibrin (IIa)
AMPLIFICATION: Thrombin activates VIII/IXa which produces more V/Xa and more thrombin
List causes of failure of fibrin clot formation and give examples
Single clotting factor deficiency usually heridatory e.g. haemophilia Multiple clotting factor deficiencies usually acquired e.g. DIC, liver failure Increased fibrinolysis (part of complex coagulopathy)
Outline a clinical approach to bleeding disorders
History (bleeding/bruising, duration) PMHx (surgery, dental extractions) DHx FHx Examination
List consequences of failure of fibrin clot formation
No characteristic clinical syndrome, can be both primary or secondary haemostatic failure
What is thrombophilia?
Deficiency of naturally occuring anticoagulants, usually heridatory, leading to an increased tendancy to develop venous thrombosis (DVT/ PE)
Protein C is converted to an anticoagulant serine protease by a complex between _____ and ______
Thrombin
Thrombomodulin
What is Von Willebrand Factor?
Acts as a glue to help platelets stick to each other and to the endothelial wall
What clotting factor does vWF carry?
Factor VIII
What is the lifespan of a platelet?
7-10 days
Following endothelial vessel wall damage, collagen is exposed and releases which factor to attract platelets to adhere?
Von Willebrand Factor
Why is platelet plug formation impaired in older people, causing easy bruising?
Lose collagen from vessel wall with age - less Von Willebrand Factor and thus less platelet adherance and aggregation
Which factor is released from damaged vascular endothelium during fibrin clot formation? Which factor does it activate?
Tissue factor
activates factor VIIa
Which factors are activated by factor VIIa, VIII and IXa in fibrin clot formation?
V
Xa
