Flashcards in Clotting Cascade Deck (12):
What are the stages of haemostasis?
1) Vascular phase
2) Platelet phase
3) Coagulation phase
What are the components of the first stage of haemostasis?
Vascular phase: damage to call causes vasoconstriction. Damage to endothelial cells causes release of factors and expression of surface factors to make them "sticky".
What is released by endothelial cells during the vascular phase of haemostasis?
-Tissue factor (factor III)
-Prostacyclin (-ve feedback, causes vasodilation, inhibits platelet plug formation)
What are endothelins?
Primary hormones in vascular phase of haemostasis. Stimulate smooth muscle contraction, division of endothelial cells, smooth muscle cells and fibroblasts (repair damaged site).
What occurs when a platelet becomes attached to a damaged endothelial surface?
-Swelling: becomes large and irregular
-Contraction of contractile proteins: granule release (ADP, thromboxane and Ca2+ ions ==> attract nearby platelets.)
What is contained in platelet granules?
Two types: alpha and dense
-Alpha: growth factors e.g. fibrinogen and PDGF
-Dense: non-proteins (thromboxane, serotonin adrenaline, histamine, calcium, ATP and ADP).
Negative feedback regulation of platelet plug formation?
-Prostacyclin (from endothelium)
-WBCs release inhibitory proteins
-Plasma enzymes: degrade ATP
What is the clotting cascade?
Two separate pathways (intrinsic and extrinsic) --> join to form common pathway.
Begins ~30s after initial.
Ultimately causes activation of fibrin to fibrinogen.
What initiates the intrinsic clotting pathway?
Exposure of blood to collagen (or other damaged surface) leading to formation of factor V.
What activates the extrinsic clotting pathway?
Damaged endothelial cells release factor III (tissue factor).
Leads to formation of VIIa-tissue factor complex.
What is the common pathway?
X activated (by VIIa or Va) to form Xa (aka prothrombinase). Prothrombin --> Thrombin.
Fibrinogen --> fibrin.