Hematology- platelets Flashcards
characteristics of platelets
NOT CELLS
- small fragments of megakaryocytes
- formation regulated by thrombopoietin
- blue staining outer region, purple granules
- granules contain serotonin, CA2+, enzymes, ADP, and platelet derived growth factor (PDGF)
all formed elements…
come from hemocytoblasts
hemocytoblasts -> megakaryocyte -> platelets
circulating platelets
- form a temporary plug to help seal leaks in blood vessels
- circulating platelets are kept inactive but mobile by NO and prostacyclin from endothelial cells of blood vessels
hemostasis (clotting)
fast series of cascade rxns to stop bleeding. rxn started by platelets and results in activated prothrombin and then fibrinogen
- vascular spasm
- platelet plug formation
- coagulation (clotting)
vascular spasm
- vasoconstriction of damaged blood vessel
- caused by:
direct injury
chemicals released by endothelial cells and platelets
pain reflex
platelet plug formation
positive feedback loop
at site of blood vessel injury, platelets:
1. stick to exposed collagen fibers with the help of von willebrand factor (plasma protein)
2. swell, become sticky and spiked and release chemicals
- ADP, causes more platelets to stick and release their contents
- serotonin and thromboxane enhance vascular spasm and coagulation
coagulation
- transformed from liquid to gel
- reinforces the platelet plug with fibrin threads
OCCURS IN THREE PHASES:
1. make prothrombin activator (intrinsic and extrinsic pathways)
2. prothrombin –> thrombin
3. thrombin causes fibrinogen to form into fibrin
intrinsic pathway
- HAPPENS WHEN EXPOSED TO NEGATIVE CHARGE
- blood clots in its own
extrinsic pathway
secretion of tissue factor to bypass steps to clot QUICKER
clot retraction
*pull sides of wound tight… causes creation of prothrombin activator
*happens after coagulation
- actin and myosin in platelets contract within 30-60 minutes
- platelets pull on fibrin strands, squeezing serum from the clot
serum
plasma WITHOUT clotting factors
clot repair
clot forms in 3-5 minutes
- platelet derived growth factor (PDGF) stimulates cells to come out of quiescence (G0). stimulates division of smooth muscle cells and fibroblasts to rebuild blood vessel wall
- vascular endothelial growth factor (VEGF) stimulates endothelial cells to multiply and restore endothelial lining
fibrinolysis
*get clot outta the way to get rid of it
- begins within 2 days
- plasminogen in clot -> into plasmin
- plasmin is a fibrin digesting enzyme
- mesh goes away and cells divide to fill that space
factors limiting clots
2 ways:
- removal and dilution of clotting factors
- inhibition of activated clotting factors (NO)
inhibition of clotting factors
- most thrombin is bound to fibrin, and prevented from spreading
- heparin, anticoagulent, inhibits thrombin activity
