Lecture 7: Haemostasis

Question 1

What are the three steps of primary haemostasis?

Answer 1

Platelet adhesion (via vWF-GPIb).

Platelet activation (collagen-GPVI → shape change/granule release).

Platelet aggregation (fibrinogen-αIIbβ3 bridges).

Question 2

What is the role of vWF?

Answer 2

Anchors platelets to exposed collagen; circulates as multimers (cleaved by ADAMTS-13).

Question 3

Name two platelet granules and their contents.

Answer 3

α-granules: vWF, fibrinogen, PDGF.

Dense granules: ADP, Ca²⁺, serotonin.

Question 4

Which vitamin K-dependent factors are part of the coagulation cascade?

Answer 4

II, VII, IX, X (mnemonic: “1972” → Factors 1, 9, 7, 2).

Question 5

Compare the extrinsic and intrinsic pathways:

Answer 5

Extrinsic: Triggered by tissue factor (TF) + FVIIa → rapid.

Intrinsic: Activated by contact (e.g., collagen) → slower.

Both converge at FXa (common pathway).

Question 6

What is the end goal of secondary haemostasis?

Answer 6

Generate fibrin to stabilize the platelet plug.

Question 7

How is a clot broken down?

Answer 7

tPA converts plasminogen → plasmin → degrades fibrin → D-dimer.

Question 8

Name two natural anticoagulants and their targets.

Answer 8

Antithrombin III: Inhibits thrombin, FXa, IXa.

Protein C/S: Degrade FVa/VIIIa.

Question 9

What does each test measure?

Answer 9

PT: Extrinsic pathway (FVII).

APTT: Intrinsic pathway (FVIII, IX, XI, XII).

TT: Fibrinogen → fibrin conversion.

PFA-100: Platelet function (collagen/ADP/epinephrine).

Question 10

Why is sodium citrate used for coagulation tests?

Answer 10

Chelates Ca²⁺ (reversibly) to prevent clotting in vitro.

Question 11

Compare warfarin and heparin:

Answer 11

Warfarin:
Oral (vitamin K antagonist)
Targets II, VII, IX, X
Slow onset (days)
Antidote: Vitamin K

Heparin:
IV/SC (activates antithrombin)
Targets thrombin, FXa
Immediate effect
Antidote: Protamine

Question 12

How does aspirin work?

Answer 12

Irreversibly inhibits COX-1 → blocks thromboxane A₂ (platelet inhibitor).