Primary Hemostasis Flashcards
What are the two mechanisms involved in vasoconstriction?
Nerve reflex and endothelin which is secreted by the endothelial cells which act on the smooth muscle to contract
What two molecules are involved in vasodilation?
Nitrous oxide and prostacycline (vasodilator and platelet inhibitor)
What are the four steps in primary hemostasis?
Vasoconstriction, platelet adhesion, platelet activation and degranulization, platelet aggregation
What is vasoconstriction?
Stoppage of blood flow
At what platelet count does bleeding occur?
Less than 50,000 per µL
What is the normal size of platelets?
0.5 – 3.0 µm
What is the normal platelet count?
150,00 – 450,000 per µL
Where do platelets come from?
Parent cells are megakaryocytes and are produced in the bone marrow; each megakaryocyte produces 2,000 platelets
What are platelets?
Platelets (thrombocytes are small (0.5-3.0 ᶙm), colorless disk-shaped cell fragment without a nucleus, found in large numbers in blood and involved in clotting
What are two types of glycoprotein receptors?
Glycoprotein Ib and glycoprotein IIb/IIa
What role do platelets have in hemostasis?
They are blood cells whose function is to react to bleeding from damaged blood vessels by clumping to form a clot.
What is platelet adhesion?
d. The attachment of platelets to nonplatelet surfaces, which occurs after trauma when platelets contact exposed collagen fibers of the subendothelium of blood vessels
What is Von Willabrand factor? What four places is it found?
A large glycoprotein present in blood plasma and produced (found) in endothelium, platelets, and endothelial cells.
Following injury, what is the role of VWF?
VWF comes into contact with site of injury and binds tightly with the collagen that has been exposed; VWF then binds with the GP IIb/IIIa (docking stations) on the platelets.
What happens during platelet activation?
Activation happens when VWF and the platelet receptor IIb/IIIa bind, this causes the plates to change shape and degranulation occurs
