2 - haemostasis

Question 1

what are the components of normal haemostatic system?

Answer 1

1. formation of platelet plug - primary haemostasis
2. formation of fibrin clot - secondary haemostasis
3. fibrinolysis
4. anticoagulant defences

Question 2

what happens in primary haemostasis?

Answer 2

= formation of platelet plug

endothelial wall damaged exposing collagen & releasing von willebrand factor & other proteins. platelets bind to collagen via ADP & VWF. platelets secrete thromboxane A2 etc so aggregation at site of injury. platelets stick together with glycoprotein IIb/IIIa.

Question 3

what happens in secondary haemostasis?

Answer 3

= formation of fibrin clot

platelets have -ve charged phospholipids. they release ca2+ which sticks to surface. negatively charged coagulation factors attracted and stick on surface. tissue factor (tf) released which activated clotting factor VII, which activated V & X. they activate prothrombin (II) to thrombin (IIa). thrombin converts fibrinogen to fibrin

Question 4

what does failure of forming platelet plug lead to?

Answer 4

1. spontaneous bruising or purpura
2. mucosal bleeding
3. intracranial haemorrhage
4. retinal haemorrhages

Question 5

what screening test done for primary haemostasis?

Answer 5

platelet count

Question 6

what happens in fibrinolysis?

Answer 6

plasminogen broken down to plasmin by tissue plasminogen activator (tPA). plasmin breaks down fibrin to fibrin degradation products

Question 7

what are tests for fibrin clot formation?

Answer 7

1. prothrombin time = put blood in tubes & spin in lab. add in phospholipid & tissue factor & calcium. you can measure how long takes for clot to form
2. activated partial thromboplastin time = add in different thing which activate different factors, VIII & IX which make clotting factor V or X through different pathway

Question 8

what are naturally occuring anticoagulants?

Answer 8

1. serine protease inhibitors = antithrombin binds to thrombin & switches off
2. protein C & S = switch of factor VIII and V

Question 9

what is thrombophilia?

Answer 9

= deficiency of naturally occuring anticoagulants may be hereditary which causes increased tendency to develop venous thrombosis (DVT/PE)