9. Haemostasis 1 Flashcards Preview

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Flashcards in 9. Haemostasis 1 Deck (25):

Define haemostasasis

The stopping of blood flow


How is coagulation initially stimulated?

Stimulated by vessel injury - there is an exposure of collage and this leads to the 'platelet release reaction'
The vessel injury also results in the release of tissue factor, which activates the 'coagulation cascade'

NB. vessel injury also stimulates vasoconstriction to reduce blood flow


Briefly describe the platelet release reaction

Release of serotonin which leads to vasoconstriction
Release of Thromboxane A2 and ADP which results in platelet aggregation
Release of platelet phospholipid which activates the coagulation cascade

SO all the components of anticoagulation are dependant on the platelet release reaction


What is meant by primary haeomostasis and briefly describe this

Primary haemostasis refers to the formation of the primary platelet plug
This occurs due to the platelet aggregation and reduced blood flow created from the platelet release reaction


What is meany by secondary haemostasis and briefly describe this

This is the coagulation cascade
Leads to the formation of thrombin and then fibrin which transforms the primary haemostatic plug into a stable haemostatic plug
I.e. stabilises the primary platelet plug when the plug alone is insufficient to stop the haemorrhage


What is Von Willebrand factor (vWF)?

This is a glycoprotein that circulates in the plasma
vWF is made by cells in the bone marrow and by endothelial cells
Mediates the adherence of platelets to one another and to the sites of vascular damage
Binds to GpIb, GpIX and GpV on the surface of platelets and this activates aggregation of platelets as well as collagen formation


What is Von Willebrand disease?

Autosomal inheritance
Deficient or defective VWF
Means that these patients cannot clot properly and are prone to excessive bleeding


Name two common platelet disorders and they they occur

Bernard Soulier syndrome - lack of GpIb

Glanzmann's syndrome - lack of GPIIb


What are the three stages of primary haemostasis?



Give the mechanism of action of primary haemostasis

(Remember primary haemostasis is the formation of the platelet plug)

1. Adhesion
Damage to the endothelium exposes the subendothelium
The endothelial cells then release VWF
VWF anchors platelets to the subendoethelium via GpIb binding

2. Activation
Thrombin combines with it's receptor on the platelet surface
The platelet then undergoes a shape change
There is a release of thromboxane A2 and ADP from the platelet

3. Aggregation
TXA2 and ADP uncap the fibrinogen receptor on the platelet
The fibrinogen then attaches to GPIIb/GPIIIA
Platelets are then linked together
A water soluble clot is formed


Describe the importance of tissue factor in secondary haemostasis (coagulation cascade)

Tissue factor is necessary for the initiation of coagulation
It is present on the subendothelial tissue
It comes into direct contact with blood upon trauma
It is factor VII dependent
The tissue factor leads to the activation of coagulation factors in the blood at the site of the injury


What is the roll of fibrin in the coagulation cascade?

Fibrin polymers form long chains between platelets in the primary plug to form a more stable clot


How is fibrin formed?

Coagulation factors adhere to platelets and form catalytic complexes
These complexes cause the formation of thrombin
Thrombin converts fibronogen to fibrin


What are the three pathways of the coagulation cascade?

Intrinsic pathway
Extrinsic pathway
Final common pathway


Give the mechanism of the intrinsic pathway of the coagulation cascade

How is this pathway activated?

Activated by subendothelial collagen exposure from trauma

XII --> XIIa
XI --> XIa
IX -->IXa (using Ca2+)
X --> Xa (using VIII)


Give the mechanism of the extrinsic pathway of the coagulation cascade

How is this pathway activated?

Activated by tissue factor released by damaged blood vessels

VII --> VIIa (using tissue factor)
X --> Xa


Give the mechanism of the final common pathway of the coagulation cascade

Prothrombin --> thrombin (using Xa, V and Ca2+)
Fibrinogen --> fibrin (using thrombin)
XIII --> XIIIa (using thrombin)
Fibrin --> stable fibrin clot (using XIIIa)


How is the intrinsic pathway of the coagulation cascade activated?

Activated by sunendothelial collagen exposure from trauma


How is the extrinsic pathway of the coagulation cascade activated?

Activated by tissue factor released by damaged blood vessels


What is APTT (activated partial thromboplastin time)?

The time taken for the intrinsic pathway of the coagulation cascade


What is the prothrombin time?

The time taken for the extrinsic pathway of the coagulation cascade?


What is the thrombin time?

Time taken for the final common pathway of the coagulation cascade


Describe how haemophilia affects the coagulation cascade

Haemophilia A affects factor VIII
Haemophilia B affects factor IX


What are the symptoms of haemophilia?

Soft tissue bleeds
Bleeding into joint cavities
Psoas bleeding
Intracranial bleeds
Bleeding at operative sites


What components are responsible for the regulation of coagulation?

Protein C and S
Fibrnolytic clot