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Blood > Haemostasis - 1 > Flashcards

Haemostasis - 1 Flashcards

1
Q

Describe the three main factors involved in haemostasis.

A

Vessel Constriction
Platelets - activation, adhesion, platelet plug
Coagulation cascade activated = fibrin

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2
Q

When would increased bleeding or thrombosis occur?

A

Vessel wall disease
Abnormal numbers of functions of platelets
Reduced or abnormal coagulation proteins or inhibitors of coagulation

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3
Q

Purpura

A

Bleeding into the skin due to reduced platelet count

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4
Q

Ecchymoses

A

Large purpura

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5
Q

Petechiae

A

Small pinpoint sites of bleeding from capillaries

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6
Q

What is needed for normal homeostasis?

A

Normal blood vessel walls
Normal endothelium
Normal platelet numbers and function
Normal amounts of functionally normal coagulation proteins
Normal blood flow and normal inhibitors of platelet activation and coagulation

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7
Q

Name the platelet activation receptors.

A 
Collagen - GpIa
vWF - GpIb 
Thromboxane A2 
Adrenaline
ADP 
Thrombin 
Serotonin
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8
Q

Name the steps of platelets involved in bleeding.

A

Adhesion
Activation
Platelet plug formation

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9
Q

What happens in platelet adhesion?

A

GPIV/GPIa binds to collagen

GPIb binds to vWF

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10
Q

Describe the events occurring in platelet activation.

A

Shape change - more spherical and pseudopods extended
Secretion of granules - alpha and dense to recruit and activate more platelets
Production of thromboxane A2 (TXA2) via COX pathway - more platelets activated by TXA2
GpIIa and GPIIb activated - Fibrinogen or vWF binds to GpIIa/GpIIb and platelets aggregate
Microvesicles budded off platelet cell membrane

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11
Q

What effect does shearing stress from turbulent blood flow have on platelet activation?

A

May partially activate platelets

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12
Q

What are dense granules formed of?

A

Ca
ADP
Serotonin - vasoconstriction and platelet activation

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13
Q

What are alpha granules formed of?

A

Fibrinogen, vWF, Factor V, Factor VII

Platelet specific: platelet factor 4 (anti-heparin)

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14
Q

Why is the platelet plug essential for stopping bleeding?

A

Ensures activating coagulation factors are not washed away

Activated coagulation factor concentrations increase to the levels needed for a fibrin clot to be produced

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15
Q

What is the bleeding time test?

A

Standardized assessment of microvascular bleeding

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16
Q

When is the bleeding time test not undertaken?

A

Uncooperative px (children)
Elderly px with thin skin
Abnormal skin
Taking anti-platelet meds

17
Q

What is the PFA-100 test?

A

Tests platelet function, replaces bleeding time test

18
Q

What affects the PFA-100 results?

A

Platelet numbers, platelet function abnormalities

19
Q

What factors affect both the bleeding time test and PFA-100 test?

A

Diet factors - garlic, ginger, chocolate, alcohol

20
Q

What are important questions to ask before surgeries?

A

Do you bleed from small cuts for longer than other people? (significant if >5min)
Do you get spontaneous nosebleeds? - how long and how often
Do you bruise more easily than others - how often do you get a bruise? (monthly or more)
How large are the bruises (significant if often >2.5cm)

NB: these questions are not reliable for carrier states,

21
Q

Where are platelets produced?

A

In the bone marrow by megakaryocytes

22
Q

What is the process of platelet production called? Describe this process.

A

Thrombopoiesis
Megakaryoblast –> megakaryocyte –> platelets
25% of platelets are kept in the spleen, after splenectomy, platelet count increases by 20%

23
Q

What is thrombocytopenia?

A

Reduced platelet count

24
Q

Name the features of mild thrombocytopenia.

A

Platelet count: 50-100
Increased bleeding with trauma or surgery if below 100
Slow oozing from cut surface

25
Q

Name the features of moderate thrombocytopenia.

A

Platelet count: 20-50

Bruising more common

26
Q

Name the features of severe thrombocytopenia.

A

Platelet count: less than 20
Bruising with minimal trauma, petechiae, may be spontaneous
Life threating bleeding into brain, from gut, retroperitoneal

27
Q

What is the effect of aspirin on bleeding time in thrombocytopenia?

A

Prolongs bleeding time by 3 min.

However hype responders and non-responders exist.

28
Q

Name the causes of thrombocytopenia.

A

Reduced production of platelets
Shortened survival of platelets
Dilutional
Sequestration in spleen

29
Q

What causes a reduction in the number of platelets?

A

Marrow depression: chemo, radiotherapy, drugs/chemicals
Marrow failure due to marrow replacement: cancer of bone marrow, secondary marrow infiltration
Selective depression of megakaryocytes: viral infections, drugs and chemicals
Aplastic anaemia (rare)
Hereditary (rare)

30
Q

What is responsible for shortened platelet survival?

A

Increased destruction of platelets - autoimmune, drug-induced antibody
Activation/Consumption of platelets - immune, disseminated intravascular coagulation (gram negative septicaemia)

31
Q

Describe the dilutional cause for thrombocytopenia.

A

Bleeding followed by massive transfusion

32
Q

Describe how sequestration in the spleen causes thrombocytopenia.

A

Pooling of 30-80% of platelets in an enlarged spleen (splenomegaly)

33
Q

Name factors causing acquired platelet function defects.

A

Anti-platelet drugs - aspirin, clopidogrel

Other drugs - NSAIDs

34
Q

How else might a person have a platelet function defect?

A

From inheritance

Severe Inherited Platelet Function Defects are rare.

35
Q

Describe the relationship between platelets and endothelium in normal blood flow.

A

Platelets do no normally adhere to the endothelium.
This is because the endothelium secretes NO and prostacyclin which dilates the blood vessels and inhibits platelet activation.

36
Q

Describe the flow of normal blood.

A

Velocity of flow is faster in the centre of blood vessels
Lower shear stress at endothelial cell surface
Central red cell rich zone
Peripheral plasma and platelet rich zone

37
Q

What do endothelial cells do?

A

Clear ADP released by activated platelets

38
Q

What happens hen the endothelium is activated?

A

P-selectin expressed - platelets may adhere

Endothelin is produced - enhances vasoconstriction

39
Q

What happens when endothelial cells are lost?

A

Vessel constriction - nerve reflexes
Platelets adhere to connective tissue - collage and subendothelial vWF
Platelet activation and release reaction - release of ADP, release of serotonin (vessel constriction), TXA2 synthesized
More platelets activated and aggregated - plug forms, bleeding from small vessels stops

Blood (8 decks)

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