Haemostasis Flashcards
What are the 5 major steps of haemostasis?
Vascular spasm, formation of a platelet plug, conversion to a clot by reinforcement with fibrin, tissue repair and gradual removal of clot
What is the role of ADP in platelet plug formation?
Sticky platelets
What is the role of serotonin in plug formation?
Vasoconstrictor
What is the role of thromboxane A2 in plug formation?
Vasoconstrictor and activates platelets
What is triggered when the platelet plug is formed?
Coagulation cascade
What is the intrinsic pathway of the coagulation cascade?
XII–>XIIa
XI–>XIa
IX–>IXa
X-Xa via VIIIa
What is the extrinsic cascade? (trauma)
VII–>VIIa
X–>Xa via tissue factor
What is the final common pathway?
Xa via Va converts prothrombin to thrombin which converts fibrinogen to fibrin which is acted on by XIII1 to form a cross-linked fibrin clot
Where are the 4 calcium/vitamin K dependent sites of the coagulation cascade?
IX–>IXa
VIIIa and tissue factor for X–>Xa
Va for prothrombin to thrombin
What is the role of prostacyclin in clotting?
Inhibits adhesion and aggregation
What is the role of nitric oxide in clotting?
Inhibits platelet adhesion
What is the role of the liver in clotting?
Synthesises bile salts for the absorption of vit K in the GI tract and synthesises clotting factors
What enzyme breaks down a clot?
Plasmin
How does antithrombin work?
Inactivates thrombin and inactivates factors Xa and IXa, anticoagulant
What conditions lead to excessive bleeding?
Clotting defects and platelet deficiency