Platelets and Hemostasis Flashcards
(25 cards)
Platelets are form by?
Fragmentation from megakaryocytes
life span of platelets
degenerate in 10 days
who stimulates production of platelets
Thrombopoietin
What is hemostasis
Process of stopping bleeding.
3 phases of hemostasis
- Vascular spasms
- Platelet plug formation
- Coagulation (blood clotting)
Coagulation also known as?
blood clotting
vascular spasm role and function
Smooth muscle contracts causing vasoconstriction and causes blood
vessel to spasm, the spasms will narrow the blood vessel decreasing blood loss
factor that trigger vascular spasm
▪ Direct injury to vascular smooth muscle
▪ Chemicals released by endothelial cells and platelets
▪ Reflexes initiated by local pain receptors
Briefly describe the platelet plug formation
1) Damaged endothelium expose underlying collagen fibers
2) Platelets adhere (粘) to collagen fibers via von Willebrand factor
3）Anchored platelets release chemicals to attract more
platelets
4）Platelets pile (堆) up to form a platelet plug
Two pathway for coagulation cascade
intrinsic pathway
extrinsic pathway
what is required to activate both coagulation pathway
phospholipids
what is coagulation cascade
Activation of a series of coagulation factors or clotting factors
coagulation process in detail
1)Injured tissues release tissue factor (TF)
2) PF3 (a phospholipid) interacts with TF, blood protein clotting factors, and calcium ions to trigger a clotting cascade Involves clotting factors numbered I to XIII
3) Prothrombin activator coverts prothrombin to thrombin
4) Thrombin will joins fibrinogen proteins into hair-like molecules of insoluble fibrin
5) Fibrin forms a meshwork
The clot is stabilized by a platelet-induced process called?
clot retraction
As clot retraction is occurring, the vessel is healing, _________ stimulates smooth muscle cells and fibroblasts to divide and rebuild the wall
Platelet-derived growth factor (PDGF)
________ stimulates endothelial cells to multiply and restore the endothelial lining
Vascular endothelial growth factor (VEGF)
Fibrinolysis meaning
Removes unneeded clots after healing
Plasmin function
act as a fibrin-digesting enzyme
how to limit clot growth
Thrombin:
binds to fibrin threads, helping to form stable blood clots. Fibrin prevents clots from getting too big.
Antithrombin III:
stops extra thrombin from causing unwanted clots, while heparin boosts antithrombin III’s action, helping to prevent clot formation.
why is antithrombic substance important in blood clotting
because it can prevent undesirable clotting by prevent platelet adhesion (粘附)
What cause the undesirable clotting
thrombus and embolus
How thrombus cause the undesirable clotting
if large enough it can obstruct the blood flow
How embolus cause the undesirable clotting
It will break away from the vessel and floats freely in the bloodstream, may get stuck at the narrow blood vessels and cause a blockage
low platelet count in the blood will cause?
Thrombocytopenia
