Coagulation Flashcards
What protects from traumatic blood loss and arrests hemorrhage at the site of injury?
Hemostasis and Coagulation
What are the stages of coagulation?
- Platelet activation (aggregation)
- Coagulation (blood clot)
- Clot Retraction (fibrinolysis)
Platelets
not true cells, cytoplasmic fragments of megakaryocytes
no nuclei, have bodies and granules containing platelet activating and clotting factors
Megakaryocyte
immediate precursor of platelets
What is the normal concentration of platelets in the blood?
250,000 per cubic mm
How long do platelets remain functional?
7-10 days
Thrombopoietin
glycoprotein produced by the liver
stimulates production and differentiation of megakaryocyte
Where do platelets aggregate selectively?
In damaged blood vessels
dense bodies
vesicles in each platelet containing pre-made chemicals
ADP and Ca2+
granules
vesicles for all invasive purposes
von Willebrand factor
fibrinogen
What contracts to cause clot retraction?
actin microfilaments and myosin intrinsic factor
activated platelets + fibrinogen =
platelet aggregation
When a blood vessel is damaged, the endothelium is disrupted and an underlying layer of what is exposed?
collagen
How are circulating platelets activated?
exposed collagen
contact with collagen is facilitated by vWF released by damaged endothelial cells and other activated platelets
What do activated platelets do?
change shape
release soluble factors that activate other circulating platelets (ADP and TXA2)
Glycoprotein Ia and Glycoprotein VI
bind collagen
facilitate loose platelet adhesion
Glycoprotein Ib-V-IX
binds to vWF anchored on collagen
facilitates strong platelet adhesion
Glycoprotein IIb/IIIa
activated when other glycoprotein receptors are engaged with their ligands
when activated captures fibrinogen
Normal Hemostasis process
- Adhesion
- Amplification
- Aggregation
Amplification
Glycoprotein IIb/IIIA activation
platelets release ADP
a few adhered platelets recruit more platelets to the site
ADP receptors
P-type purinergic receptors
binding of ADP to P2Y12 activates glycoprotein IIb/IIIa on circulating platelets
Thromboxane/prostaglandin endoperoxide receptor
binding of TXA2 to this induces platelets to change shape
TXA2 generated in activated platelets via cyclooxygenases
Formation of a platelet plug
- exposed collagen binds and activates platelets
- release of platelet factors
- attracts more platelets
- aggregate into platelet plug
Intact endothelium releases prostacyclin (PGI2) which inhibits?
platelet adhesion
Initial platelet adhesion to collagen creates a local accumulation of what?
ADP and TXA2 that may overcome PGI2
Thrombocytopenia
bleeding disorder caused by insufficient platelets
platelet count is less than 100,000/mm3
one type is heparin-induced