HaemostasisPresented by Dr Azza Serry

Learning Objectives

Definition . Clotting mechanism . What keeps blood in fluid status Control of blood clotting and fibrinolytic systems

Haemostasis disorders

Components

Haemostasis is the arrest of bleeding.

This requires the combined activity of vascular ,platelet ,and plasma factors .

Vascular : vasoconstriction of injured blood vessel .

Platelet : platelet plug formation . Plasma factors : clotting cascade activation .

What keeps the body fluidity

Endothelial cells secrets nitric oxide and prostacyclin which promote blood fluidity by :

prevent platelet stasis

dilate intact blood vessels .

Endothelial cells expresses TPA and antithrombin III .

These mediators are no longer produced when vascular endothelium is disrupted .

Coagulation cascade

Clotting cascade

Coagulation is activated by two mechanisms :

Extrinsic :initiated by activation of factor VII upon ad mixture of plasma and tissue factor (damaged tissue )

Intrinsic : initiated by activation of factor XII upon contact with non endothelial surface . ( glass )

Regulatory feedback mechanis

ms

Regulatory feedback mechanisms counterbalance the tendency of clots to form :

① inactivation of coagulation factors , antithrombin III : inactivate thrombin , VIIa ,IXa ,

Xa ,XIa. protein C ,and S, inactivate factors Va and VIIIa .

② fibrinolysis , (tissue plasminogen activator TPA ) by endothelial cells

↓ plasminogen → plasmin ↓

fibrin → fibrin degradation products ③ Hepatic clearance of activated clotting factors

Regulation of fibrinolysis : vascular endothelium and activated platelet release plasmin inhibitor .

Haemostatic diorders

Hypercoagulable state :inherited due to deficiency of natural anticoagulant ( protein C and S)

Acquired tendency to thrombosis in malignancy or contraception

Bleeding diathesis : congenital or acquired

Congenital : Haemophilia A and B Von Willibrand disease Acquired:

Bleeding diathesis Congenital disorders

Haemophilia

Sex – linked disorder ,present by bleeding into soft tissues ,and weight bearing joints .

Haemophilia A : defect factor VIII

Haemophilia B : defect factor IX

Treated by replacement .

Von Willibrand disease

Von Willibrand factor : adhere platelet to subendothelium ,carrier of factor VIII .

Von Willibrand disease : Presents by menorrhagia ,epistaxis .

Treated by factor VIII concentrate

Acquired disorders

Thromocytopenia Causes : decreased production ,bone marrow aplasia .

increased consumption : splenomegaly .

Non steroidal anti-inflammatory ,Aspirin ,interfere with platelet adhesion .

Vitamen K deficiencyCofactor for production of factors II , VII ,IX ,X .Causes : hepatocellular disease ,malabsorption ,Treated by parenteral Vitamen K ,FFP ( fresh frozen plasma) .

HEPATIC FAILURE

Hepatic failure : decrease synthesis of coagulation factors except factor VIII,synthesis of inhibitors ( protein C ,S ) , decreased clearance of activated factors .

Renal failure : decrease aggregation of platelet .