Haemostasis- platelet 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 primary haemostasis?

A

-formation of a platelet plug

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3
Q

what is secondary haemostasis?

A

-formation of fibrin clot

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4
Q

would a paper cut use primary or secondary haemostasis?

A

primary haemostasis (formation of platelet plug

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5
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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6
Q

where are platelets formed and what from ?

A

in bone marrow from ‘budding’ megakaryocytes

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7
Q

average life span of a platelet?

A

7-10 days

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8
Q

how is the life span of a platelet clinically relevant?

A

Aspirin will affect platelet for its whole life span (life span is 7-10 days)
-Stop aspirin 7 days before operation so patient wont bleed as there will be new platelets

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9
Q

structure of a platelet?

A

-platelets are small anucleated discs

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10
Q

role of Von Williebrand Factor (VWF)?

A

Von Williebrand factor helps platelets stick together AND binds to factor 8 (so if have defect, this factor will fall)

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11
Q

explain primary haemostasis?

A

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

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

Von Willebrand Factor: helps with platelet adhesion AND binds to factor 8

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12
Q

what could cause failure for platelet plug formation?

A

Causes: Vascular, Platelets, Von Willebrand Factor

Vascular no collagen can lead to bleeding
* Hereditary: Marfans
* Acquired: Vit C deficiency (scurvy), HSP vasculitis, increase in age

Platelets
* Reduced number (thrombocytopenia) - majority are aquired
-Reduced production (marrow problem)
-Increased destruction (coagulopathy) e.g. DIC, autoimmune e.g. immune throbocytopenic purpura, hypersplenism

* Reduced function -majority are Aquired -Drugs: aspirin, NSAIDs, renal failure

Vol Willebrand Factor autosomal dominant, most common haemolytic disease

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13
Q

vascular causes of failure for platelet plug formation?

A

Vascular (no collagen can lead to bleeding)
-Hereditary: Marfans
-Acquired: Vit C deficiency (scurvy), HSP vasculitis, increase in age

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14
Q

platelet causes of failure for platelet plug formation?

A

Can either be due to reduced number of platelets (either due to reduced production or increased destruction) or reduced function

Reduced production examples:
-bone marrow suppression

Increased destruction examples:
-DIC, immune thrombocytopenic purpura

Reduced function examples:
-drugs such as aspirin, renal failure or von willebrand factor disorder

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15
Q

consequences of failure to form a platelet plug?

A

-Spontaneous Bruising and Purpura
-Retinal haemorrhages
-Mucosal bleeding:
* Epistaxes
* Gastrointestinal
* Conjunctival
* Menorrhagia
* Intracranial haemorrhage

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16
Q

what are screening tests for primary haemostasis?

A

Check platelet count
(no simple screening tests for other components of primary haemostasis)

17
Q

describe the coagulation pathway

A

Platelets are full of -ve phospholipid, when platelets are activated, +ve charge calcium is recruited and binds to platelets phospholipid. Blood clotting factors are -ve charged and so are attracted

-when endothelial damage TF binds to clotting factors VIIa
-VIIa and TF activate V and Xa
-V/Xa cause II (prothrombin) to become IIa (thrombin)
-IIa (thrombin) causes (I) fibrinogen to become (Ia) fibrin
-also IIa (thrombin) can activate VIIIa and IXa which activate more V and Xa creating a positive feedback loop

18
Q

what is the intrinsic coagulation pathway?

A

clotting factors VIII (8) and IXa (9a)

19
Q

what is the extrinsic coagulation pathway?

A

TF and VIIa

sEvEn= Extrinsic

20
Q

what clotting factor plays an important role in combining the pathways?

A

Xa

X marks the spot

21
Q

how do platelets bind to subendothelial collagen?

A

Platelets bind to subendothelial collagen via Glycoprotein 1b and Von Willebrand Factor.

22
Q

what can measure the extrinsic pathway?

A

prothrombin time

23
Q

what clotting factors are affected- increased PT and normal APTT?

A

clotting factor VII

24
Q

what clotting factors are affected- normal PT and increased APTT?

A

Clotting factors:
VIII
IX
XI
XII

25
Q

what clotting factors are affected- increased PT and increased APTT?

A

-common factor (rare)
-multiple clotting factors