Hemostasis and Coagulation Flashcards
Define hemostasis and describe the 3 mechanisms of hemostasis
hemostasis is the stoppage of blood flow.
vascular constriction: neural reflex and TXA2, along with other chemical mediators, help with vasoconstriction, though the most powerful vasoconstrictor is endothelin I.
formation of the platelet plug:
activation: platelets travel to a damaged vessel wall, change from smooth discs to spiny spheres, and exposing glycoprotien receptors on their surfaces.
adhesion: happens when the platelet receptor binds to vWF (von Willebrand factor, an important protein molecule that leaks into the injured tissue from the plasma) at the injury site, linking the platelet to exposed collagen fibers.
aggregation: the secretion of the platelet granules mediates it. ADP is a mediator of platelet aggregation.
blood coagulation: coagulation cascade, where the fibrin strands come together to create a meshwork that cements platelets and other blood components together to form the clot.
review platelets: structure, normal lab number, formation, role in hemostasis, hematemesis, menorrhagia.
structure: irregularly shaped smooth discs (will change to spiny spheres when they start helping with clotting at an injured tissue)
Lab: A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood.
formation: platelets are formed by thrombopoietin in the liver, kidney, smooth muscle, and bone marrow
role in hemostasis: stop bleeding by building a clot.
role in hematemesis: because people have lost blood, a platelet test is important because you don’t want to give them medicines that could further diminish platelet supply.
menorrhagia: where the platelets do not function correctly, resulting in heavy menstural bleeding.
explain the intrinsic and extrinsic pathways for coagulation in terms of how they are initiated and how rapidly they work
the intrinsic pathway is initiated by factor XII. This pathway is a relatively slow process. It causes clotting in 1 to 6 minutes.
The extrinsic pathway is initiated by the release of tissue factor and it is a lot faster as it can cause clotting in 15 seconds.
describe the parts of the terminal pathway for the intrinsic and extrinsic pathways and why they are the same.
the terminal steps in both factors are the same–> the activation of factor X and the conversion of prothrombin to thrombin. Thrombin then acts as an enzyme to convert fibrinogen to fibrin, the material that stablizes a clot.
define fibrinolysis.
the enzymatic breakdown of the fibrin in blood clots.
when should a person be assessed for bleeding disorder?
blood in stool,
bleeding that is hard to stop or control,
wounds that don’t heal up good,
etc?
define: petechiae, purpura, ecchymosis,
petechiae: Petechiae are pinpoint, round spots that appear on the skin as a result of bleeding. The bleeding causes the petechiae to appear red.
purpura: A rash of purple spots due to small blood vessels leaking blood into the skin, joints, intestines, or organs.
Ecchymosis: NOT THE SAME AS BRUSING!
a skin discoloration that results from bleeding underneath the skin and usually larger than 1 cm or . 4 inches.
define: melena, hematuria, hemoptysis
melena: dark sticky feces with or without visible blood.
hematuria: Blood in the urine. may range from very obvious to microscopic and not visible at all.
hemoptysis: Small amounts of blood mixed with sputum (or more seriously, large amounts of bright red blood) brought up by a forceful cough.
define thrombocytopenia and list causes
thrombocytopenia is when you have a reduction in platelet number (less than 150,000 per microliter)
causes: decreased platelet production, increased sequestration of platelets in the spleen, or decreased platelet survival.
