Reflex vasoconstriction to prevent blood loss, vWF is stimulated by damaged endothelial cells and binds with collagen allowing platelets to adhere, activated platelets release TXA2 and ADP to attract more platelets
What is secondary hemostasis?
the clotting cascade, clot retraction, clot dissolution
Common pathway of the Clotting cascade
Factor X + Calcium = Factor Xa + Calcium cleaves Prothrombin to produce Thrombin triggers Fibrinogen + Calcium > Fibrin (monomer) > Fibrin (polymer)
Extrinsic pathway of the Clotting cascade
Factor VII + Calcium produces Factor VIIa which with Calcium triggers the common pathway (faster pathway than intrinsic)
Intrinsic pathway of Clotting cascade
Factor XII > Factor XIIa > Factor XI > Factor XIa > Factor IX + Calcium > Factor IXa which with Factor VIIIa and Calcium triggers the common pathway
How does clot retraction occur?
the actin and myosin of the platelets contract to pull the fibrin tighter around the platelets
What causes clot dissolution?
tissue plasminogen activator (tPA = clot buster!) cleaves plasminogen to form plasmin, plasmin digests the fibrin
What blood test is used to evaluate the extrinsic pathway?
PT/INR (prothrombin time/international normalized ratio), also used to monitor Coumadin effect
What blood test is used to evaluate the intrinsic pathway?
PTT (partial thromboplastin time), also used to monitor Heparin effects
What can cause disseminated intravascular coagulation (DIC)?
Trauma, Sepsis, Cancer. Tissue factor release leads to massive act of the clotting cascade
Why is DIC especially deadly?
platelet stores and clotting factors are exhausted so hemostasis cannot be achieved, fibrinolysis is also activated inhibiting thrombin and platelet aggregation (leads to bleeding), fibrin is deposited intravascularly leading to thrombosis production, hemolytic anemia, and tissue ischemia