Hemostasis Flashcards
Thrombopoietin
Protein hormone w/ same amine terminal as EPO.
Produces by liver and kidney.
TPO binds to what?
mpl on a platelet, megakaryocyte to activate the JAK/STAT to produce platelets.
Control of platelet production: high amount of platelets
Lots of TPO bound to mpl. Platelet internalizes TPO and destroys it.
Control of platelet production: low amounts of platelets
Little TPO is bound - nothing destroyed.
Mutation in TPO receptor is associated with:
Polycythemia vera (too many RBCs).
Platelets contain (8)
Actin Myosin Mitochondria ER remnants COX1 Fibrin stabilizing factor Platelet derived growth factor Serotonin
Platelet CMs express (3)
Glycoproteins (become sticky)
Phospholipids
Receptors for collagen
4 steps of hemostasis
- vascular spasm
- formation of platelet plug
- formation of blood clot/coagulation
- repair of damage
Vascular spasm
SM contracts w/o neuronal stimulation.
Serotonin and thromboxane a2 are platelet factors that also contribute to vasoconstriction.
Neural reflex in the spasm
Not necessary or sufficient for spasm to occur, but adds to its potency.
Formation of the platelet plug
When vessel wall is damaged, collagen is exposed. Platelets bind to collagen.
Von Willebrand factor binds the collagen and platelet.
Platelet swells and extends podocytes.
Platelets aggregate.
Formation of the platelet plug might be sufficient in:
Nose bleeds, skin, bleeds ,etc.
Coagulation
Need to get rid of excess fluid and solidify the clot.
Platelets bind fibrin polymers together via fibrin receptor on platelet.
Actin and myosin in platelet cause contraction (Ca needed).
Role of platelet-derived growth factor in damage repair
PDGF stimulates growth fibroblasts to differentiate into SM, CT, etc to repair the damage.
Pathway of clot removal
Thrombomodulin + thrombin activates protein C.
Protein C inactivates the t-PA inhibitor, allowing t-PA to convert plasminogen to plasmin which lyses fibrin.
