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Haematology > Haemostasis and bleeding disorders > Flashcards

Haemostasis and bleeding disorders Flashcards

1
Q

What is haemostasis?

A

The arrest of bleeding and the maintenance of vascular patency

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2
Q

What is needed for haemeostasis?

A

Permanent state of readiness, prompt response, localised response, protection against unwanted thrombosis

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3
Q

What are the components of a normal haemostatic system?

A
  • Formation of platelet plug - primary haemostasis
  • Formation of fibrin clot - secondary haemostasis
  • Fibrinolysis
  • Anticoagulant defences
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4
Q

How are platelets formed?

A

Formed in the bone marrow by budding from megakaryocytes

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5
Q

Describe the structure of platelets

A

Small anucleate discs with a mean life span of 7-10 days

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6
Q

What is the function of platelets and what is the mechanism behind this function?

A

Endothelial damage exposes collagen and releases Von Willebrand Factor (VWF) and other proteins to which platelets have receptors - platelet adhesion at the site of injury

There is then secretion of various chemicals from the platelets, which leads to aggregation of platelets at the site of injury

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7
Q

Name some causes of failure of the platelet plug

A
  • Vascular e.g. age, steroids, Henoch-Schonlein purpura, scurvy, Marfan’s syndrome
  • Thrombocytopenia - reduced production e.g. marrow problem or increased destruction
  • Reduced function of platelets - drugs e.g. aspirin, renal failure
  • Von Willebrand factor deficiency
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8
Q

What can happen as a consequence of failure of platelet plug formation?

A

Spontaneous bruising and purpura, mucosal bleeding (epistaxes, GI, conjunctival, menorrhagia), intracranial haemorrhage, retinal haemorrhages

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9
Q

How is primary haemostasis screened for?

A

Platelet count

No simple screening tests for other components of primary haemostasis

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10
Q

What are some causes of failure of fibrin clot formation?

A
  • Single clotting factor deficiency - usually hereditary e.g. haemophilia A and B - isolated prolonged APTT
  • Multiple clotting factor deficiencies - usually acquired e.g. disseminated intravascular coagulation (DIC), liver disease, vitamin K deficiency - multiple screening tests prolonged
  • Increased fibrinolysis - usually part of complex coagulopathy
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11
Q

What are the possible consequences of failure of fibrin clot formation?

A
  • No characteristic clinical syndrome
  • May be combined primary/secondary haemostatic failure
  • Pattern of bleeding depends on single/multiple abnormalities and the clotting factors involved
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12
Q

What are some screening tests for fibrin clot formation?

A
  • Prothrombin time
  • Activated partial thromboplastin time
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13
Q

Name some naturally occurring anticoagulants

A

Serine protease inhibitors, protein C and protein S

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14
Q

What is thrombophilia?

A

Deficiency of naturally occurring anticoagulants, may be hereditary

Increased tendency to develop venous thrombosis (DVT/PE)

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15
Q

How is a fibrin clot formed in terms of clotting factors?

A
  • Endothelial damage -> Tissue Factor forms a complex with factor VIIa -> Va/Xa are activated as a result
  • Factor Va/Xa allows the conversion of prothrombin into thrombin
  • Thrombin then stimulates factor VIII/IXa to activate more V/Xa and thus convert more prothrombin into thrombin
  • Thrombin allows fibrinogen to be converted into fibrin
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16
Q

What are some causes of peripheral platelet destruction?

A
  • Coagulopathy e.g. disseminated intravascular coagulation (DIC)
  • Autoimmune e.g. immune thrombocytopenic purpura (ITP)
  • Hypersplenism
17
Q

What are the causes of Von Willebrand deficiency?

A

Acquired

Hereditary - autosomal dominant, common, variable severity (generally mild)

18
Q

What is the most common cause of primary haemostatic failure?

A

Thrombocytopenia - usually acquired, due to either marrow failure or peripheral destruction

19
Q

What can cause multiple clotting factor deficiencies which then lead to failure of fibrin clot formation?

A
  • Liver failure
  • Vitamin K deficiency/warfarin therapy
  • Complex coagulopathy - DIC
20
Q

What is used to investigate cause of failure of fibrin clot formation?

A
  • APTT - activated partial thrombplastin time
  • PT - prothrombin time
  • Both will be prolonged in clotting factor deficiencies
21
Q

Where are coagulation/clotting factors synthesised?

A

In hepatocytes - thus reduced in liver disease/failure

22
Q

Why is vitamin K important in coagulation?

A

Factors II, VII, IX and X are carboxylated by vitamin K, which is essential for function

23
Q

Where do we get vitamin K from, where is it absorbed and what does it need for absorption?

A
  • Sources - diet and intestinal synthesis
  • Abosrbed in upper intestine
  • Requires bile salts from gall bladder for absorption
24
Q

What can cause vitamin K deficiency?

A
  • Poor dietary intake - typically patients in ICU with parenteral feeding
  • Malabsorption
  • Obstructive jaudive i.e. gall stones block bile salts from travelling from the liver to the intestine for vitamin K absorption
  • Vitamin K antagonists - warfarin
  • Haemorrhagic disease of the newborn
25
Q

What is disseminated intravascular coagulation?

A
  • Excessive and inappropriate activation of the haemostatic system - primary, secondary and fibrinolysis
  • Microvascular thrombus formation - end organ failure
  • Clotting factor consumption - bruising, purpura and generalised bleeding
26
Q

Describe the mechanism of fibrinolysis

A
  • Plasminogen is converted to plasmin
  • Plasma allows conversion of fibrin to fibrin degradation products (FDPs) e.g. D-Dimers
27
Q

What are some causes of DIC?

A
  • Sepsis
  • Obstetric emergencies e.g. placenta praevia
  • Malignancy
  • Hypovolaemic shock
28
Q

How is DIC treated?

A

Treat the underlying cause

Replacement therapy:

  • platelet transfusions
  • plasma transfusions
  • fibrinogen replacement
29
Q

What is haemophilia?

A

An X-linked, hereditary disorder in which abnormally prolonged bleeding recurs at one or a few sites on each occasion

X-linked so only seen in men!

30
Q

What is the difference between haemophilia A and B?

A
  • Haemophilia A - factor VIII deficiency, 5 times as common
  • Haemophilia B - factor IX deficiency
31
Q

What occurs as a result of haemophilia?

A
  • No abnormality of primary haemostasis i.e. platelet plug formation is unaffected
  • Bleeding from medium to large blood vessels
  • Mild, moderate and severely affected families depending on factor VIII/IX levels
32
Q

What are the clinical features of severe haemophilia?

A
  • Recurrent haemorthroses - most commonly ankle, knee and elbow joints, in that order
  • Recurrent soft tissue bleeds - bruising in toddlers
  • Prolonged bleeding after dental extractions, surgery and invasive procedures

Haematology (22 decks)

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