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Path Processes > Haemostasis > Flashcards

Haemostasis Flashcards

1
Q

Define haemostasis

A

The stopping of haemorrhage

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2
Q

What is clotting?

A

The process where liquid blood becomes a solid mass when it makes contact with connective tissue

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3
Q

Describe the process of haemostasis in 3 steps

A
  1. A severed artery contracts to decrease the pressure downstream
  2. Exposed collagen and vWF activates platelets. A primary haemostastic plug of activated platelets forms at the injury. (takes s-mins)
  3. A secondary haemostatic plug forms as fibrin filaments stabilise the fragile platelet plug (takes about 30 mins)
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4
Q

There are a number of different things that can activate platelets, name 4

A

1) Exposed collagen surfaces

2) ADP (released by activated platelets and injured RBC to amplify platelet response)
3) Thromboxane A2 - a powerful platelet aggregator
4) Thrombin - converts fibrinogen to fibrin, presense informs platelets that clotting sequence is active

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5
Q

What 4 things do platelets do once they are activated?

A

1) stick to exposed subendodthelium (basement membrane of collagen) by binding to von Willebrand factor receptors
2) Aggregate with other platelets
3) Swell and change shape to become sticky, spiny spheres
4) Secrete factors that help with platelet plug grow e.g. fibrinogen, ADP and thromboxane A2

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6
Q

How does aspirin decrease platelet aggregation?

A

Aspirin irreversibly inactivates COX enzymes which are responsible for production of thromboxane A2

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7
Q

Which enzyme converts circulating fibrinogen to fibrin?

A

Thrombin

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8
Q

Why can’t thrombin circulate in an active state?

A

Would get inappropriate blood clotting

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9
Q

Which factors of clotting cascade require vitamin K for their synthesis?

A
  • II
  • VII
  • IX
  • X
  • Protein C (anticoagulant)
  • Protein S (anticoagulant)
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10
Q

What is the intrinsic clotting pathway?

A

The intrinsic pathway is activated by damage to a vessel wall - it involves all the factors that are contained in blood

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11
Q

What is the extrinsic clotting pathway?

A
  • Pathway needs tissue factor (thromboplastin/ III) which is present outside of blood
  • It is triggered by thromboplastin release from damaged cells next to an area of haemorrhage
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12
Q

Where do the intrinsic and extrinsic pathways combine/?

A

They combine when factor X becomes activated to Factor Xa

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13
Q

What is the role of factor Xa in the clotting cascade?

A

Factor Xa convert prothrombin –> Thrombin

Thrombin converts fibrinogen –> fibrin

Fibrin cross links the clot

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14
Q

Give an overview of the Extrinsic clotting pathway

A

Trauma to extravascular cells releases thromboplastin (FIII)

Factor III converts Factor VII→ VIIa

Factor VIIa and factor III complex converts factor X→Xa

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15
Q

Give an overview of the Intrinsic clotting pathway

A
  • Factor XII→ XIIa
  • XIIa converts XI→ XIa
  • XIa converts IX→IXa
  • Factor IXa complexes with factor VIIIa to convert factor X→Xa
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16
Q

What are the 3 main natural anticoagulants?

A
  • antithrombin III
  • Protein C
  • Protein S
17
Q

What is fibrinolysis? Give an overview

A

The enzymatic breakdown of fibrin by plasmin

  • Plasmin circulates as inactive plasminogen
  • It is activated by tPA (tissue plasminogen activator)
  • Fibrin is broken down into breakdown products; D-dimers
18
Q

Where is plasminogen made?

A

In the liver

19
Q

Aside from tPA, name 2 other things that can activate plasminogen

A
  • Urokinase (found in urine)
  • Streptokinase (found in streptococci)
20
Q

What are the side effects of therapeutically giving plasminogen activators?

A
  • Bleeding -mainly from gums or nose
  • can occur in the brain (serious but less common)
21
Q

In what conditions would you see elevated levels of D-dimers?

A
  • Disseminated Intravascular Coagulation (DIC)
  • DVT
  • Pulmonary Embolism
22
Q

What happens to fibrinolytic activity post surgery?

A

Fibrinolytic activity drops and remains low for 7-10days

23
Q

What is the final fate of a clot?

A
  • Eventually clots becomes organised and undergo fibrous repair
  • They are initially replaced by granulation tissue and then by a tiny scar
24
Q

What is the role of Von Willebrand factor?

A

vWF is involved in platelets adhesion to the vessel wall

It is also a carrier for factor VIII

25
Q

What are some of the clinical features of Haemophilia?

A
  • Muscle haemotomas
  • recurrent haemarthroses
  • Joint pain and deformity from joint bleeds
  • Prolonged bleeding post dental extraction
  • Life threatening bleeding post op/ post trauma
  • Intracerebral haemorrhage
26
Q

Give an overview of haemophilia A

A
  • deficiency of factor VIII
  • X linked recessive
  • treated with infusions of recombinant factor VIII
27
Q

Give an overview of haemophilia B

A
  • deficiency of factor IX
  • X linked recessive
  • treated with infusions of recombinant factor IX
  • also known as Christmas disease
28
Q

Do you see petechia in haemophiliacs?

A

No

this is due to bleeding from capillaries which is typically seen in vasculitis or abnormalities in platelets

29
Q

What would you expect to see in the blood results of a patient with haemophilia A?

A
  • Platelet count normal
  • Bleeding time normal
  • Prothrombin time normal
  • APTT is prolonged (a measure of intrinsic pathway)
  • low factor VIII assay
30
Q

What would you expect to see in the blood results of a patient with haemophilia B?

A
  • Platelet count normal
  • Bleeding time normal
  • Prothrombin time normal
  • APTT is prolonged (a measure of intrinsic pathway)
  • low factor IX assay
31
Q

What is von Willebrand Disease?

A
  • A deficiency or abnormality in von Willebrand factor
  • The most common inherited bleeding disorder
  • Usually autosomal dominant
  • Reduced factor VIII amount/ activity
  • Abnormal platelet adhesion to vessel wall
32
Q

What is the common pattern of bleeding seen in von Willebrand disease?

A

Bleeding from mucous areas

33
Q

What blood test will be elevated in vWF Disease?

A

Increase bleeding time

Increased APTT

34
Q

What is thrombocytopenia?

A

a platelet count of <100 x10 9/L

Will see spontaneous bleeding from small vessels in:

  • Skin
  • GI tract
  • Genitourinary tract
35
Q

What blood results will you see in a patient with thrombocytopenia?

A
  • Prolonged bleeding time
  • Normal PT and APTT
36
Q

Give 4 causes of thrombocytopenia

A
  1. Decreased platelet production - bone marrow infiltration by malignancy, drugs, chemo, measles, B12 and folate deficiency
  2. Decreased platelet survival due to immune destruction (DIC)
  3. Sequestration- in splenomegaly
  4. Dilutional- due to massive blood transfusions, blood stored >24hrs does not contain platelets
37
Q

What is DIC?

A

Disseminated Intravascular Coagulation

  • Activators of clotting get into the blood causing micro thrombi in circulation
  • process consumes platelets, fibrin and coagulation factors so patient may experience haemorrhage
  • Not a disease itself but a complication of other conditions
38
Q

What conditions may cause DIC?

A
  • Sepsis
  • severe trauma
  • extensive burns
  • childbirth complications
  • malignancy
  • snake bites

Path Processes (12 decks)

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