Formation of a platelet plug Flashcards
Effects of injury on vessel walls
Disrupts endothelium and exposes underlying connective-tissue collagen fibres
what adheres to collagen, and how?
platelets adhere to collagen.
via intermediary: von Willebrand factor (vWF) - plasma protein secreted by endothelial cells and platelets
vWF binds to collagen, changes its formation, then is able to bind to platelets
what does binding of platelets to collagen trigger?
triggers platelets to release contents of secretory vesicles
what chemical agents are in secretory vesicles, and what do they do?
e.g ADP and serotonin
act locally to induce multiple changes in metabolism, shape and surface proteins of the platelets (platelet activation)
platelet activation
changing of metabolism, shape and surface proteins in platelets by ADP and serotonin from vesicles
platelet aggregation
new platelets adhere to old ones (positive feedback phenomenon) caused by platelet activation
creates a platelet plug
substance synthesised by adhesion of platelets and its function
thromboxane A2 - eicosanoid family from arachidonic acid in platelet plasma membrane
released into ECF, acts locally to further stimulate platelet aggregation and release of vesicle contents
effectiveness of platelet plug and factors affecting it
can completely seal small breaks in vessel walls.
platelets contain actin and myosin - stimulated to contract in aggregation -> compression and strengthening of platelet plug
vascular smooth muscle in damaged vessel
stimulated to contract - decreases blood flow to area and pressure.
causes of vasoconstriction
platelet activity
mediated by thromboxane A2 and chemicals from vesicles
prostacyclin/prostaglandin I2
inhibitor of platelet aggregation
eicosanoid
released by endothelial cells
nitric oxide
produced by adjacent endothelial cells
vasodilator
inhibitor of platelet adhesion, activation and aggregation
