9 - Haematology II

What elements does the haemostatic response have?

• Vasoconstriction

• Platelet adhesion and aggregation

• Clotting - coagulation phase

What is the size and appearance of a platelet?

2-3 widemetre

Small, over, no nucleus

What do platelets contain/ how are they made?

granules

megakaryocyte cytoplasm (fragments into platelets)

What is platelet production controlled by?

No of circulating platelets (negative feedback)

Thrombopoietin release

What is the normal lifespan of platelets?

7-10 days

What 3 things does a vessel injury trigger

• Vasoconstriction

• Collagen exposure

• Tissue factor

What is the pathway to a primary haemostatic plug?

• Vasoconstriction (+ seratonin from platelet activation) - reduced blood flow

• Collagen exposure → platelet adhesion → platelet activation → thromboxane → platelet activation

Primary haemostatic plug

What does platelet activation entail ?

• Shape change

• Granule secretion

• Activation GPIIb/IIa

How is the stable haemostatic plug produced?

Tissue factor → blood coagulation cascade → thrombin → fibrin

How is soluble plasma converted to insoluble rigid fibrin?

• Fibrinogen → Fibrin

• Enzyme Thrombin

• Factor XIII stabilises fibrin

What factor stabilises fibrin?

XIII

What is the Extrinsic pathway?

Initiation of coagulation

• Tissue factor binds to FVII → Tissue Factor-FVIIa complex

• Binds to FX and activated it to become FXa

What factors are involved in the extrinsic pathway?

Tissue factor

FVII

Tissue factor FVIIa complex

FX

FXa

What is the intrinsic pathways of the coagulation phase?

Factor IX and co-factor VIII

Activates FX - Fxa

More slowly than extrinsic pathway

Which is faster, the intrinsic or extrinsic coagulation phase?

Instrinsic phase

What factors are involved in the intrinsic pathway?

Factor IX and co-factor VIII

FX and FXa

What is the common pathway of the coagulation phase?

Prothrombinase (FXa and FVa as a co-factor)

Activated prothrombin → THROMBIN

THROMBIN converts FIBRINOGEN → FIBRIN

What vitamins and minerals do you need for bloodclotting?

Calcium and vitamin K

What is vitamin K necessary for?

Certain clotting factors in the liver including prothrombin

What natural ‘anticoagulants’ are there in normal plasma?

• Antithrombin - inhibits thrombin

• Heparin - released by basophils and mast cells - co-factor that accelerated actions of Antithrombin

How many blood group systems are there?

35

What differentiates blood groups?

Antigens on red blood cell membrane

What are the blood groups with the most clinical significance?

ABO and Rh(D) blood group systems

What antigens and antibodies does someone with Group A blood group have?

A antigen on RBC, Anti-B antibodies in plasma

Which blood groups are dominant and recessive?

A + B = dominant

O = recessive

What is Rh+ or - determined by?

Presence of the D antigen

Does a Rh (-) individual contain anti-Rh(D) antibodies?

Not usually

What is required for the presence of anti-Rh(D) antibodies?

Sensitisation by exposure to Rh+ RBCs

What would cause Haemolytic disease of a newborn?

Rh negative mother and Rh positive baby

What do you transfuse in an emergency?

transfuse with O Rhesus negative: universal donor