blood coagulation, haemostasis

Question 1

what are the principles of haemostasis?

Answer 1

maintains stable physiology: blood goes from liquid to solid in areas where needed

Question 2

what is haemostasis a balance between

Answer 2

• coagulation (blood changes from liquid to gel)

- fibrinolysis (breakdown of fibrin in blood clots)

Question 3

what occurs to the balance of haemostasis when thrombosis occurs?

Answer 3

• coagulation factors are activated
• increase in platelets which plug up the whole and allow coagulation factors to interact
• decrease in fibrinolytic factors & anticoagulant proteins

Question 4

what occurs to the balance of haemostasis when there is excessive bleeding?

Answer 4

• increase in fibrinolytic factors & anticoagulant proteins
• decrease in coagulant factors and platelets

Question 5

haemophilia

Answer 5

deficient in clotting factors -> excess bleeding

Question 6

thrombocytopaenic

Answer 6

low blood platelet count

Question 7

ecchymosis

Answer 7

symptom of most bleeding disorders

- excessive bruising: a discoloration of the skin resulting from bleeding underneath, typically caused by bruising.

Question 8

primary haemostasis

Answer 8

Vasoconstriction (immediate)
Platelet adhesion (within seconds)
Platelet aggregation and contraction (within minutes)

Question 9

secondary haemostasis

Answer 9

Activation of coagulation factors (within seconds)

Formation of fibrin (within minutes)

Question 10

fibrinolysis

Answer 10

Activation of fibrinolysis (within minutes)

Lysis of the plug (within hours)

Question 11

how are platelets drawn to area of damaged vessel?

Answer 11

Damage to the blood vessel -> barrier is broken -> exposes underlying very adhesive proteins e.g. collagen -> platelets recognise this & stick to the area using VWFactor

Question 12

Role of VWf

Answer 12

Acts as an anchor to platelets

Question 13

what happens when platelets adhere to a region?

Answer 13

Platelets change: develop increased surface area, sudopodia (can stick in neatly & perform their function)
On top of that more platelets accumulate

Question 14

how are platelets attracted to collagen?

Answer 14

• VWF binds to extracellular collagen & GpIb-IX-V complex
• the GpIIb-III undergoes a conformational change
• structural changes in platelets
• negatively charged phospholipids: pro-coagulant surface

Question 15

describe the initiation of coagulation

Answer 15

• cell expressing tissue factor
• forms a complex with factor 7a
• factor 7a converts 10 to 10a
• 10a joins with 5a to produce thrombin
• factor 2 leads to platelet aggregation & accumulation
• amplifies thrombin production

Question 16

amplification of coagulation

Answer 16

Burst of thrombin: drives production of Fibrin from fibrinogen

Question 17

what happens in haemostasis for someone who has haemophilia A

Answer 17

• deficiency of factor 8 which is why the big thrombin burst doesn’t happen
• symptoms involve bleeding just by walking
• blood in the joint is toxic

Question 18

what happens in haemostasis for someone who has haemophilia B

Answer 18

• don’t get the thrombin burst and so there is poor blood clot

Question 19

what does each reaction in the waterfall hypothesis require?

Answer 19

• Ca2+

- phospholipid

Question 20

laboratory evaluation of bleeding

Answer 20

• FBC and film
• Coagulation tests
• Platelet function
• Global tests

Question 21

how do we ensure that the haemostasis testing is accurate?

Answer 21

by ensuring the quality of the specimen submitted:
Blood is anticoagulated with 3.2 % (0.109 M) Sodium citrate
Most tubes contain 0.3 mL anticoagulant and require 2.7 mLs of blood.

Question 22

what are the main principles of clotting tests?

Answer 22

• incubate plasma with reagents necessary for coagulation

- measure the time taken for fibrin clot to form

Question 23

what is prothrombin time?

Answer 23

evaluates the extrinsic pathway

wait until you see the formation of yellow jelly (fibrin) 8-10 seconds

Question 24

what is activated partial thromboplastin time?

Answer 24

evaluates the intrinsic pathway

Question 25

what is thrombin time?

Answer 25

sensitive to defects in conversion of fibrinogen to fibrin

Question 26

D-dimer testing

Answer 26

A measure of the D-dimer, a fibrin degradation product
found elevated in the situation of enhanced fibrinolysis (Thrombosis, DIC)

Not specific for thrombosis also elevated as an acute phase reactant

A Negative result is useful if clinical suspicion of VTE is low