Introduction To Haemostasis Flashcards
What is Haemostasis?
The consequence of a tightly regulated process, it maintains a fluid status in normal vessels, whilst permitting rapid formation of a homeostatic clot at a site of vascular injury.
What are 3 components of Haemostasis?
Vascular wall (endothelium), platelets, coagulation cascade.
What are 3 processes involved in Haemostasis?
Contraction of vessel wall, formation of platelet plug at site, formation of fibrin clot to stabilise.
What happens when a vessel is injured?
Results in platelet: adhesion, activation/secretion, aggregation.
Describe platelet adhesion.
Damage to vessel wall, exposure of underlying tissues, platelets adhere to collagen via vWF receptor.
Describe platelet activation
Secretes granules containing ADP, thromboxane and other substances to become activated and activate other platelets. Provide some coagulation factors.
Describe platelet aggregation
Cross linking of platelets to form a platelet plug, provides some stability but friable.
What are the tests for clotting defects?
3 basic tests, performed on platelet poor plasma: activated partial thromboplastin time, prothrombin time, thrombin time.
Describe APTT
Intrinsic pathway, if prolonged, suggests a deficiency in one of the factors: (Factor VIII, IX, XI, XII) -> VIII (haemophilia A) + IX (haemophilia B)
Describe PT
Extrinsic pathways most commonly due to a factor VII deficiency.
What are examples of natural anticoagulants?
Protein C, Protein S, antithrombin
Describe mechanism of activated protein C.
Thrombin binds to an endothelial cell receptor called thrombomodulin, this activates protein C then inactivated factors VIIIa and Va. Protein S is a cofactor for activated protein C.
Describe mechanism of antithrombin III.
Plasma protein that inactivate thrombin and several other clotting factors. Activated by heparin on the surface of endothelial cells. Prevents the spread of a clot by rapidly inactivating clotting factors that are carried away from the immediate site of the clot by the flowing blood.
Describe thrombocytopenia
Deficiency of platelets in blood resulting in bleeding into the tissues, bruises and slow blood clotting after injury. Presents with purpura, petechiae, mucosal bleeding, epistaxis, menorrhagia.
Describe haemophilia A and its treatment
X-linked recessive, congenital lack of factor VIII (severity depends on amount present), prolonged APTT and normal PT. Treated with recombinant factor VIII or DDAVP.
