Coagulation

Question 1

What is haemostasis?

Answer 1

• Processes that…
  • stop haemorrhage
  • prevent haemorrhage
  • maintain flow
• Three mechanisms
  • Cellular = platelets
  • Humoral = coagulation
  • Tissue = vessels

Question 2

What are the different clotting factors?

Answer 2

I Foolish (fibrinogen and fibrin)

II People (prothrombin and thrombin)

III Try (tissue factor)

IV Climbing (calcium)

V Pretty (proaccelerin)

VI Vicious (Va- accelerin)

VII Slopes (stable factor)

VIII After (antihemophilic factor)

IX Christmas, (Christmas factor)

X Some (Stuart-prower factor)

XI People (plasma thromboplastin antecedent)

XII Have (hageman factor)

XIII Fallen (fibrinase)

Question 3

What is factor I and Ia?

Answer 3

fibrinogen → fibrin monomer → fibrin polymers → fibrin fibrils → cross-linked fibrin polymer → dissolution into FDPs

Question 4

What is factor II and IIa?

Answer 4

Question 5

What is factor X and Xa?

Answer 5

Question 6

What is factor V and Va?

Answer 6

Question 7

What is factor IX and VII?

Answer 7

Question 8

What is factor III?

Answer 8

Question 9

What is the process of the coagulation cascade?

Answer 9

Question 10

What is factor XIII?

Answer 10

• INACTIVE enzyme
• Plasma glycoprotein (≈ 0.03 µM)
• 1,335 amino acids; MW ≈ 320 kDa
• Two chains:
• FXIIIA 694 resid
• FXIIIB 641 resid
• Activated by thrombin [R|G]
• Transglutaminase EC: 2.3.2.13 → crosslinks glutamine to lysine in fibrin. Ca²⁺ is a co-factor.

Question 11

What is the prothrombin time (PT)?

Answer 11

• Performed with citrated blood sample
• Triggered by thromboplastin & Ca²⁺
• thromboplastin = TF (FIII) & phospholipid (PS/PL)
• Pathway to fibrin via FVII
• FVIIa → FXa → FIIa (thrombin) → FIa (fibrin)
• Defects in FVII, FX, FV, FII, FI could all prolong PT
• For example:
• FVII deficiency
• warfarin-induced (PT more sensitive to warfarin)

Question 12

What is the Activated Partial Thromboplastin Time (aPTT)?

Answer 12

• Performed with citrated blood sample
• Triggered by an activator and partial thromboplastin
• activator = negatively charged surface, e.g., kaolin
• partial thromboplastin = phospholipid (PS/PL)
• Pathway to fibrin via FXII
• FXIIa → FXIa → FIXa → FXa → FIIa (thrombin) → FIa (fibrin)
• Defects in FXII, FXI, FIX, FVIII, FX, FV, FII, FI could all prolong aPTT
• For example:
• FVIII or FIX deficiencies (Haemophilia A & B)
• heparin-induced (aPTT more sensitive to heparin)