Haemostasis

Question 1

Define haemostasis

Answer 1

Stopping of bleeding

Question 2

Define thrombosis

Answer 2

Formation of solid mass of blood with circulatory system

Question 3

What does the haemostatic system consist of

Answer 3

Many proteins which interact with platelets and blood vessel endothelial cells

Question 4

What are the 5 stages of the haemostatic mechanism

Answer 4

Vascular phase (vasoconstriction)
Platelet plug formation
Clot formation
Clot retraction
Fibrinolysis

Question 5

What happens in the vascular phase

Answer 5

Constrictor to limit blood loss and slow flow
Vascular smooth muscle contracts when vessels are damaged
First response

Question 6

What are platelets attracted to

Answer 6

Exposed extracellular matrix at the damaged site

Question 7

What do platelets adhere to

Answer 7

Vessel wall and each other

Question 8

What do activated platelets release

Answer 8

Thromboxane A2 and thrombin

Question 9

How do platelets work

Answer 9

Adhere to connective tissue via platelet receptor that recognises glycoproteins on connective tissue
Assisted by von willebrand factor which binds collagen
ADP, thromboxane A2 and thrombin are released recruiting more platelets

Question 10

What is fibrinolysis

Answer 10

Dissolving clot after bleeding has stopped

Question 11

What is the clotting cascade

Answer 11

A series of reactions where inactive proteins are converted into active proteins

Question 12

What are the 2 clotting cascade pathways

Answer 12

Intrinsic and extrinsic

Question 13

What is the intrinsic pathway

Answer 13

Required factors are in blood
Activated by blood exposure to sub endothelial surfaces
Negatively charged surfaces exposed by endothelial damage
Prekallikrein converted to kallikrein setting off a cascade of protease reactions

Question 14

What is the extrinsic pathway

Answer 14

Initiating factor outside the blood
Activated by tissue factor released after cellular injury and binds to factor VII
TF is a protein found on sub endothelial cells
Cascade starts as thrombin activates factor VII

Question 15

What forms the clot in the clotting cascade

Answer 15

Fibrin polymers

Question 16

What does warfarin do the the clotting cascade

Answer 16

It is a competitive antagonist of vitamin K inhibiting the synthesis of vitamin K dependent clotting factors (II, VII, IX and X)
Increasing warfarin increases slow clotting therefore low vitamin K leads to reduced production of some clotting factors

Question 17

What does a lack of factor VIII lead to

Answer 17

Failure of intrinsic pathway

Question 18

What are 4 symptoms of haemophilia A

Answer 18

Frequent, severe bleeding
Bleeding into joints
Intracranial bleeding
Prolonged aPTT in screening, confirmed with factor VIII assay

Question 19

What are treatment options there for haemophilia A

Answer 19

Replacement factor VIII
But the body can generate antibodies to this after time
Ideal would be gene therapy

Question 20

What is haemophilia B

Answer 20

Much rarer than A
X linked recessive
Defect in gene for factor IX
Intrinsic pathway compromised and similar manifestations as A, treatment is the replace factor IX

Question 21

What is von willebrands disease

Answer 21

Most common hereditary blood clotting disorder
Autosomal dominant
Lack of vWF so compromised platelet adhesion
Excessive brushing and bleeding gums

Question 22

What is the blood flow risk factors of thrombosis

Answer 22

Stagnation
Long surgery, long periods of inactivity

Question 23

What is the endothelial or vessel wall injury risk factors of thrombosis

Answer 23

Vessel damage
Hypertension
Foreign bodies from injury or implant, bacteria
Inflammation

Question 24

What is the coagulation risk factors of thrombosis

Answer 24

Post operative
Postpartum
Deficiency of various anticoagulation factors - hypercoagulability
Cigarette smoking, oral contraceptives

Question 25

What does aspirin do to the blood

Answer 25

Prevents platelet plug formation by inhibiting COX enzymes which make thromboxane A2