Coagulation

1. General Events in Clotting
   

platelet cells activated by damage-> PF3 and/or Tissue Factor produced by platelet cells-> Factor X activated->prothrombin activator (enzyme) produced-> prothrombin conversion -----> thrombin (another enzyme) ;thrombin stimulates: fibrinogen ---->fibrin mesh

1. anticoagulant - chemical that inhibits clotting
2. procoagulant - chemical that promotes clotting
   
3. intrinsic pathway - within the damaged vessel
   

1. more Procoagulants needed (I-XIII) toward PF3 and Factor X
2. allows more "scrutiny" before clotting occurs
   

4. extrinsic pathway - in outer tissues around vessel
   

1. Tissue thromboplastin (Tissue Factor) - skips intrinsic steps straight to PF3 and Fac X
2. allows rapid response to bleeding out of vessel (clot can form in 10 to 15 seconds)
   

5. After activation of Factor X, common pathway:
   

Factor X, PF3 (thromboplastin), Factor V, Ca++ -->prothrombin activator ->prothrombin converted -> thrombin (active enzyme) ;thrombin stimulates: fibrinogen -> fibrin (meshwork) ;Ca++ & thrombin -> Factor XIII (fibrin stabilizer)

2. Clot Retraction (shrinking of clot)
   

1. actomyosin - causes contraction of platelets
2. blood serum - plasma WITHOUT clotting Factors
3. platelet-derived growth factor (PDGF) - stimulates fibroblast migration and endothelial growth
   

3. Clot Eradication (Fibrinolysis)
   

1. healing occurs over 2 - 10 days
2. tissue plasminogen activator (TPA) - causes the activation of plasminogen
3. plasminogen --> plasmin
4. plasmin degrades proteins within the clot

4. Factors Limiting Growth and Formation of Clots
   

• Limiting Normal Clot Growth
  

• blood moves to fast to allow procoagulants
• factors which interfere with normal clotting
  

• prothrombin III - deactivates thrombin
• protein C - inhibits Clotting Factors
• heparin - inhibits thrombin; prevents adherence of platelets to injured site

Category: Pathology Notes