Haemostasis Flashcards
(22 cards)
What are the three main requirements for haemostasis?
- Vasoconstriction
- Platelets
- Coagulation cascade
What role does the endothelium play in haemostasis?
The endothelium plays a regulatory role and is anti-thrombotic
What are the antiplatelet effects of the endothelium?
Prostacyclin, NO, ADPase prevent adhesion & activation
What anticoagulant effects does the endothelium have?
Anti-thrombin inactivates thrombin, thrombomodulin, protein C & protein S turn off coagulation, tissue factor pathway inhibitor stops initiation
What is the fibrinolytic effect of the endothelium?
Tissue type plasminogen activator (t-PA) breaks down fibrin
What activates thrombosis in endothelial injury?
Trauma, inflammation (cytokines), infectious agents, haemodynamic forces, plasma mediators
What are the characteristics of platelets?
Disc-shaped, granular, anucleate cell fragments
Where are platelets shed from?
Megakaryocytes in bone marrow
What is the normal platelet count range?
150 – 400 x10^9 /L
What is the primary function of platelets?
To form a platelet plug through adhesion, activation, and aggregation
What initiates platelet adhesion?
Platelets stick to exposed sub-endothelial collagen via vWF
What are the four types of von Willebrand Disease?
- Type 1: quantitative defect
- Type 2: qualitative defect
- Type 3: severe quantitative defect
- Platelet type: normal vWF but defective receptors
What does a platelet function analyser (PFA-100) measure?
The time required to occlude a capillary coated with platelet activators
What is the main role of the coagulation cascade?
To convert proenzymes to enzymes and stabilize the platelet plug
What triggers the extrinsic (tissue factor) pathway of coagulation?
Tissue injury
What is the common pathway in coagulation?
Generates thrombin which converts fibrinogen to fibrin
What laboratory tests are commonly used to investigate coagulation?
- APTT
- PT (INR)
- Fibrinogen
- Thrombin clotting time (TCT)
What does the thrombin burst result in?
A tough fibrin meshwork, trapping cells
What is the role of thromboxane A2 (TXA2) in platelet aggregation?
Amplifies aggregation, activates more platelets, constricts vessels
Fill in the blank: The enzyme cascade in coagulation is a matrix of interactions where proenzymes are sequentially activated to _______.
[enzymes]
True or False: Activated platelets secrete more vWF.
True
What stabilizes factor VIII in the coagulation process?
vWF (von Willebrand factor)
