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Haematology > Haemostasis Physiology > Flashcards

Haemostasis Physiology Flashcards

1
Q

what is haemostasis?

A

arrest of bleeding and maintenance of vascular patency

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2
Q

what is primary haemostasis?

A

formation of the platelet plug (in severe bleeding can be washed away)

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3
Q

what is secondary haemostasis?

A

formation of the fibrin clot

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4
Q

what is fibrinolysis

A

maintaining vascular patency and switching haemostasis off

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5
Q

what are platelets?

A

small anucleate discs with a lifespan of 7-10 days

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6
Q

what does endothelial wall damage cause?

A

exposes collagen and releases VWF

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7
Q

what does VWF do?

A

platelets have receptors to VWF leading to platelet adhesion at the site of the injury
also carries factor VIII

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8
Q

what do the bound platelets secrete?

A

ADP

thromboxane A2

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9
Q

what does the secretion of ADP and thromboxane A2 from the platelets cause?

A

further aggregation

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10
Q

what do platelets bind to at the site of injury?

A

subendothelial collagen via:

  • VWF
  • glycoprotein 1b
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11
Q

what allows platelets to attach to one and other?

A

GPIIbIIIa

fibrinogen

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12
Q

causes of failure of formation of the platelet plug

A

vascular
thrombocytopenia
VWF deficiency

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13
Q

what are vascular causes of failure of formation of the platelet plug?

A

lack of collagen leads to weakened endothelial walls e.g. ageing and scurvy

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14
Q

three causes of thrombocytopenia

A
  1. reduced production
  2. increased destruction
  3. functional defects
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15
Q

what causes reduced production thrombocytopenia?

A

bone marrow failure

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16
Q

what causes increased destruction thrombocytopenia?

A

coagulopathy (DIC)
AI (ITP)
hypersplenism

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17
Q

how does alcohol cause hypersplenism and thrombocytopenia?

A

alcohol causes portal hypertension and cirrhosis backs up to the spleen causing hypersplenism that traps platelets reducing count
alcohol can also have a toxic effect on the spleen

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18
Q

functional defects causes of thrombocytopenia

A

drugs (aspirin, NSAIDs)

renal failure

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19
Q

inheritance of VWF deficiency

A

AD

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20
Q

presentation of failure of primary haemostasis

A

easy bruising/ purpura/ petechiae
mucosal bleeding (epistaxis, conjunctival haemorrhage)
menorrhagia

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21
Q

diagnosis of failure of primary haemostasis

A

FBC for platelet count

22
Q

causes of failure of formation of the fibrin clot

A

single clotting factor deficiency
multiple clotting factor deficiencies
increased fibrinolysis

23
Q

what is a single clotting factor deficiency?

A

haemophilia

24
Q

causes of multiple clotting factor deficiencies

A

DIC
liver failure
vitamin K deficiency/ warfarin therapy

25
Q

presentation of failure of secondary haemostasis

A

bleeding into muscles and joints (ankles and knees)

26
Q

diagnosis of failure of secondary haemostasis

A

PT (TF/VIIa)

APTT (VIII/IXa)

27
Q

where are all coagulation factors synthesised?

A

hepatocytes

28
Q

which coagulation factors are carboxylated by vitamin K?

A

II
VII
IX
X

29
Q

what does the addition of vitamin K to coagulation factors II, VII, IX and X cause?

A

gives them a negative charge to bind to Ca2+ on phospholipids

30
Q

what does vitamin K require for absorption?

A

bile salts

31
Q

causes of vitamin K deficiency?

A 
poor dietary intake
malabsorption
obstructive jaundice
head of pancreas cancer
lack of bile salts
vitamin K antagonists e.g. warfarin
HDFN
32
Q

what are some naturally occurring anticoagulants?

A

serine protease inhibitors (anti-thrombin)
protein C
protein S

33
Q

what is thrombophilia?

A

deficiency of naturally occurring anticoagulants leading to an increased tendency to develop venous thrombosis

34
Q

action of anti-thrombin

A

binds to thrombin to switch haemostasis off

35
Q

action of protein S and C

A

bound by thrombomodulin which switches off clotting factors V/Xa and VIII/IXa

36
Q

two pathways in the coagulation cascade

A
  1. extrinsic

2. intrinsic

37
Q

what is the extrinsic pathway of the coagulation cascade?

A

TF and VIIa initiates haemostasis
act on Va/Xa
which act on prothrombin (factor II) of the common pathway
this is cleaved to form thrombin (IIa)
acts on fibrinogen (factor I) > fibrin (Ia)

38
Q

what is the intrinsic pathway of the coagulation cascade?

A

activated by IIa (thrombin) are VIIIa/IXa

these are also activated by XI and XII

39
Q

which pathway does PT measure?

A

extrinsic / factor VII

40
Q

how is the PT carried out

A

thromboplastin is added to the blood sample and timed how long it takes to clot

41
Q

normal PT

A

10-12 seconds

42
Q

what pathway does APTT measure?

A

intrinsic/ factor VIII IX

43
Q

how is the APTT test carried out?

A

a contact activator with calcium and phospholipid is added to blood and timed how long it takes to clot

44
Q

normal APTT

A

30-40 seconds

45
Q

what does a prolonged APTT indicate?

A

single clotting factor deficiency

46
Q

causes of a single clotting factor deficiency

A 
haemophilia A or B (X-linked)
XI or XII deficiency
heparin
VWF deficiency
APLS
47
Q

how VWF deficiency prolong APTT?

A

VWF carries VIII so if deficient can prolong APTT

48
Q

what does a prolonged PT and APTT indicate?

A

multiple clotting factor deficiency

49
Q

causes of multiple clotting factor deficiency

A 
heparin
warfarin 
vitamin K deficiency
liver disease
DIC
50
Q

what is tested to distinguish DIC from liver disease?

A

D-dimers

Haematology (34 decks)

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