Flashcards in Week 4 Deck (19):
List four stimuli for platelet activation
What does aPTT stand for?
activated Partial Thromboplastin Time
What does aPTT mean clinically?
aPTT = the time for clot formation in citrated plasma after the addition of Ca2+, contact activator and phosphilipid to mimic the platelet membrane
I.e measures the function of the sample's intrinsic pathway
What test would you use to measure the extrinsic pathway function of your sample?
Prothrombin time (time for clot formation of plasma after addition of Ca2+ and tissue factor)
What effect does giving low-dose aspirin therapy have, and avoid?
Inhibits platelet TXA2 formation, which inhibits aggregation of exposed platelets permanently
Cleared by liver, so largely avoid vasodilatory effects on blood vessels throughout the body
Name two drugs that aim to reduce coagulation by activating plasmin
What are the three factors predisposing to thrombosis? Which is most important?
1. Endothelial injury (most important)
2. Abnormal haemodynamics e.g blood stasis or turbulence
3. Hypercoaguability of blood
Name three things injured endothelial cells release that promotes thrombosis.
1. vWF (platelet adhesion)
2. Tissue factor (extrinsic pathway)
3. Plasminogen-activator inhibitors (suppress plasmin production and thence fibrinolysis)
How does viral infection predipose to thrombosis?
Deposition of viral antigen-antibody complexes in BV walls > complement activation > membrane attack complex punches holes in endothelial cells, causing damage
How does blood turbulence predispose to thrombosis (2 things)?
1. Creates counter currents of blood flow which create areas of blood stasis > thrombosis
2. Increases activity of intravascular procoagulant cellular and enzymatic reactions that lead to blood coagulation
How does blood stasis predispose to thrombosis (3 things)?
1. Stagnant blood becomes viscous and hypercoaguable
2. Local endothelial cells may sustain hypoxic injury and release or express pro-coagulant molecules as a result
3. Retards removal of procoagulant molecules and arrival of anticoagulant molecules from circulating blood
What does the presence of lines of Zahn signify?
That the thrombus was initially non-occlusive with continued blood flow over it
What three things influence the shape, size and colour of thrombi?
Location (rate of blood flow)
Septic or not
Under what circumstances (specifically) might a pulmonary thromboembolus lodged in a medium sized artery cause pulmonary infarction?
Anything reducing O2 supply to the lung tissue itself so anemia, pneumonia, pre-exisiting fibrosis or oedema of lungs
At whay systolic BP range would you start to see clinical consequences of hypertension?
> 160-180 mmHg
What systolic BP value is considered hypotension? What about MAP?
Systolic < 80 mmHg
MAP < 60 mmHg
What are the three major mechanisms of shock?
What are the four subsets of distributive shock?