Physiology: Blood coagulation & Hemostasis

Favoring or inducing the formation to clot

Defect due to abnormal conc. or function of coagulation factors

Small pinpoint hemorrhages in skin/mucous membranes

Larger hemorrhages in skin/mucous membranes

Reduced number of Thrombocytes

Defect (congential/acquired) in platelet function

Normal or pathologic dissolution of a fibrin clot

Disseminated intravascular coagulation

von Willebrand disease

One stage prothrombin time

Activated partial thromboplastin time

Activated clotting time

• 1. Blood vessel constriction (neural)
• 2. Platelet activation (primary (temporary) hemostatic plug & Secondrry (stable) hemostatic plug)
• 3. Coagulation activation (tissue factors, thromboplastin)
• 4. Dissolution of fibrin clot
• 5. Endothelial repair

• Arrest of bleeding. There are 5 stages.
• 1. Vascular damage>vasoconstriction>platelet adhesion
• 2. Platelet recruitment>aggregation>fibrin formation>primary hemostatic plug (fragile)
• 3. Reinforcement of stable plug with fibrin>secondary hemostatic plug (thrombus)
• 4. Dissolution of fibrin clot: clot retraction & activation of fibronolysis
• 5. Endothelial repair>degradation of fibrin clot.

• 1. Vascular endothelium
• 2. Platelets
• 3. Plasma proteins

• Anti-coagulant properties
• 1. Smooth surface, -ve charge (single protein layer)
• 2. Secretion of inhibitors of platelet function and fibrin formation: PGI₂, NO, ADPase, Tissue factor pathway inhibitor (TFPI), Thrombomodulin
• 3. Secretion of activators of fibrinolysis: Tissue plasminogen activator (t-PA), urokinase-type plasminogen activator (u-PA)
• Pro-coagulant properties
• 1. Synthesis & secretion of tissue factor (III Thromboplastin) to initiate clot formation
• 2. Adhesive proteins (von Wilebrand factor) that attach activated platelets to surface
• 3. Secretion of inhibitors of fibrinolysis: Plasminogen activator inhibitor (PAI), Thrmobin activatable fibrinolytic inhibitor (TAFI)

• 1. Platelet tests
• Platelet counts: Normal Dogs & Cats > 200,000/ul; Cattle, horse >100,000/ul
• Thombocytopenia: <20,000/ul > bleeding from small vessels
• Platelet function: measure platelet adhesion, aggregation, platelet release reaction
• 2. von Willebrand factor
• Large glycoprotein in vessel wall, made of protein polymers (multimers)
• Assays: ELISA for von Willebrand factor antigen, multimeric analyses, functional tests, genetic tests
• 3. Buccal mucosal bleeding time (BMBT)
• in vivo test for primary hemostasis (platelets, wall defects & vWF) in small animals.  Normal dogs clot in less then 4 min

• Acquired
• Thrombocytopenia (<20,000/ul eg. bone marrow dysfunction, immune-mediated)
• Acquired Thrombopathies (eg. liver failer, uremia, drug induced)
• Congenital
• von Willebrand disease (dogs, cats, pigs: delayed clotting after trauma due to weak platelet aggregates)
• Inherited Thrombopathies

• Factor I Fibrinogen (liver)
• Factor II Prothrombin (liver) (Vitamin K-dependent)
• Factor III Thromboplastin (tissue factor) (VE)
• Factor IV Calcium
• Factor V Proaccelerin, Labile factor, Accelerator globulin (VE)
• Factor VII Proconvertin, SPCA, Stable factor (liver)
• Factor VIII Antihemophilic factor (AHF, AHF-A), Antihemophilic globulin (VE)
• Factor IX Plasma thromboplastic component (PTC), Christmas factor, AHF-B (liver)
• Factor X Stuart-Prower factor (VE)
• Factor XI Plasma thromboplastin antecedent (PTA), AHF-C (liver)
• Factor XII Hageman factor, Glass factor (liver)
• Factor XIII Fibrin stabilizing factor, Laki-lorand factor (liver)
• vWH von Willebrand factor (VE)
• Pre-Ka Prekallikrein (PK), Fletcher factor (liver)
• HMW-K High molecular weight kininogen (HMWK, HF), Fitzergald factor (liver)
• t-PA Tissue-type plasminogen activator (liver)
• u-PA Urokinase-type plasminogen activator
• PL Platelet phospholipid

• Factor XII Collagen, Trauma, other activators XIIa
• Factor XI
• Factor IX XIA & Calcium IXs
• Which combines with VIIIa, ca2 and PL, to make the tenase complex, activating X in the common pathway
• Most Factors except XII get positve feedback from thrombin

• Tissue factor (III) trauma
• VII (Xa can give positive feedback here)
• III & VIIa can either directly activate X to Xa in the common pathway or go to Factor IXa to form the Tenase complex

• Factor X activated by Tenase complex or III & VIIA Xa
• Factor Xa with prothrombin (II), Ca2, PL, Va form Prothrombinase complex
• Thrombin activated by prothrombinase complex
• Activates Fibrinogen (I) to Fibrin
• Thrombin also activates XIII to XIIIa
• Fibrin and XIIIa, with calcium, form Fibrin polymers

Biosynthesis of Factor II, VII, IX, and X are dependent on Vit. K

Factors IX, X, XI, XII and Thrombin

• 1. There are 2 major pathways: intrinsic pathway or contact pathway and extrinsic pathway or tissue factor pathway
• 2. Both converge at a common point
• 3. ~13 (?) soluble factors are involved in clotting
• 4. Biosynthesis of II, VII, IX and X are dependent on vitamin K
• 5. Heparin affects factors IX, X, XI, XII and Thrombin
• 6. Most of these factors are proteases - normally inactive and sequentially activated
• 7. In birds, reptiles and marine animals, Factor XII (intrinsic pathway) is deficient - resulting in prolonged clotting time
• 8. Acquired defects (platelet defects, liver diseases, DIC) more common than hereditary defects (hemophilia) in animals

• 1. One stage Prothrombin time (OSPT or PT)
• 2. Activated Partial Thromboplastin time (APTT)
• 3. Activated Clotting time (ACT)

• For evaluating extrinsic & common pathways (defects in factor VII, V, K, Prothrombin, Fibrinogen, eg. rodenticie poisioning)
• Plasma + tissue factor + ca -> clotting time (dogs < 10 sec)

• For evaluating intrinsic & common pathways (defects in Factors XII, XI, X, IX, VIII, Prothrombin, Fibrinogen)
• Plasma + Activator of XII + PL + Ca -> clotting time (dogs < 45 sec)

• Activator (diatomaceous earth) +  whole blood -> clotting time (normal: dogs 60-90 sec. cats 160 sec): Less sensitive than APTT
• For evaluating intrinsic and common pathways (decreased platelet count)

• Vit K antagonism/deficiency
• rodenticide poisoning (dicoumarol)
• cholestatic liver disease
• Sever malabsorption
• Liver failure
• Disseminated intravascular coagulation (DIC)
• pathological activation of both coagulation mechanism & fibrinolytic system in blood vessels -> decreased thrombocytes + FDPs (eg, cause cancer, infectious diseases)
• Coagulation factor deficiency (Dogs, cats. Congenital)
• FVIII deficiency - Hemophilia A
• FIX deficiency - Hemophilia B

• 1. Clot retraction - shrinking of fibrin clot
• a. mediated by platelet contractile proteins -actin, myosin, thrombosthenin
• b. Functions - stablize clot, promote tissue repair, activate fibrinolysis
• 2. Fibinolysis - degradation of fibrin clot by plasmin

Plasminogen has to be activated to plasmin. It has both inhibitors and activators.

• Inhibitors: Plasminogen activator inhibitors (PAI 1,2,3)
• Activators: Extrinsic: Urokinase, tPA
• Intrinsic: Kallikrein, XIIa, XIa
• Exogenous: Streptokinase

The Plasmin, with alpha2-antiplamin and alpha2-macroglobulin, change fibrin to fibrin degradation products