Platelet Plug Formation Flashcards
what are the three steps in hemostasis?
- vasoconstriction
- platelet plug formation
- coagulation
what are the three steps to platelet plug formation?
- platelet adhesion
- platelet activation
- degranulation? check the powerpoint from review
- platelet aggregation
what happens during platelet adhesion?
usually endothelial cells lining the blood vessel express molecules that inhibit platelet adherence
but when a vessel is injured, normal endothelial cells are damaged/removed which exposes the subendothelial collagen fibers to the inside of the vessel
endothelial cells release vWF which binds to the exposed collagen
circulating platelets rolling through the blood vessel begin tethering on vWF-immobilized collagen through a very weak but fast interaction
what allows for circulating platelets to start attaching to vWF-immobilized collagen when there’s a blood vessel injury?
- damaged endothelial cells release vWF which binds to exposed collagen
- platelets express a protein called GPIb, which binds with vWF
this allows for platelet adhesion
the combination of collagen, vWF, and GPIb allow for platelet adhesion in the first step of plug formation
What vessel inhibitors normally prevent platelet adhesion when there isn’t any injury?
- Nitric oxide
- endothelial ADPase
- prostacycline (PGI2)
what happens during platelet activation?
after platelets adhere, they have to be activated to form a plug
platelet activation initiates when the subendothelial collagen binds to GPIb via vWF
activation triggers exocytosis of dense granules and alpha granules, leading to release of ADP, vWF, thrombin, and other chemical
modulators (including thromboxane A2, PDGF, VEGF, serotonin, and coagulation factors)
what two types of granules do platelets have and what does each secrete?
- dense granules = ADP
2. alpha granules = vWF, thrombin and growth factors
what two things happen during platelet activation?
- exocytosis of dens granules and alpha granules
2. platelets change shape to flatten and increase surface area
what helps reinforce platelet activation?
thrombin
it activates certain receptors on the platelet membrane
what receptors do activated platelets express? what do they do?
activated platelets express glycoprotein IIb/IIIa (GPIIb/IIIa) and vWF receptors
GPIIb/IIIa receptor on the platelet binds to fibrinogen
vWF receptor allows the cells to continue to adhere to exposed collagen in the broken endothelium
look at the picture…
what is thromboxane A2?
it’s secreted by platelets once they’re activated
it’s an arachidonic acid derivative that activates other platelets and induces vasoconstriction
what gets secreted by platelets once they’re activated?
- thromboxane A2 (TxA2)
- serotonin
- platelet dervived growth factor (PDGF)
- vascular endothelial growth factor (VEGF)
what is serotonin?
it’s secreted by platelets once they’re activated
short-lived and has a vasoconstrictive effect associated with inflammation during vessel injury
what are PDGF and VEGF?
they’re secreted by platelets once they’re activated
they’re growth factors involved in angiogenesis
what is angiogenesis?
growth of new blood vessels following injury
