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Haematology > Platelets I > Flashcards

Platelets I Flashcards

1
Q
  1. What is the diameter of platelets
A

1-4 µm in diameter

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2
Q
  1. What is the blood concentration of platelets
A

Blood concentration = 150,000-400,000 per µl of blood

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3
Q
  1. How long do platelets circulate in the blood
A

Circulate for 7-10 days

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4
Q
  1. How are platelets removed from the blood
A

Removed by macrophages in the liver and spleen

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5
Q
  1. What is the ultrastructure of platelets enclosed by
A

Enclosed by plasma membrane with open canalicular system

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6
Q
  1. What is expressed on the surface of platelets
A

Surface expression of glycoprotein receptors

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7
Q
  1. What type of ring of cytoskeleton does a platelet have
A

Ring of microtubule cytoskeleton

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8
Q
  1. What organelles can be found in platelets
A

Mitochondria
Golgi apparatus
Endoplasmic reticulum

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9
Q
  1. What does the endoplasmic reticulum store in platelets
A

stores Ca2+ (calcium)

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10
Q
  1. What do platelet granules store
A

stores LOTS of mediators important for haemostasis

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11
Q
  1. What 8 mediators are found in platelet granules
A

Clotting factors (see later)
ADP/ATP
Calcium
Serotonin
Prostaglandins
Thromboxanes
Fibrin-stabilising factor
Platelet-derived growth factor (PDGF)

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12
Q
  1. Define coagulation
A

the process through which blood changes from a liquid to a clot (thicker)

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13
Q
  1. Define fibrinolysis
A

removal of a clot (thrombus) after it has formed

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14
Q
  1. Outline what happens during the vascular spasm (phase 1) phase of primary haemostasis
A
  1. Endothelial cell contraction
  2. Release of chemical mediators/hormones
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15
Q
  1. What does endothelial cell contraction allow to happen
A

allows exposure of underlying collagen matrix to bloodstream

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16
Q
  1. What happens after the release of chemical mediators/hormones
A
  1. smooth muscle contraction
  2. proliferation of endothelial, smooth muscle and fibroblast cells
17
Q
  1. What does phase 1 result in and what does this do for the injured vessel
A
  • Results in vasoconstriction.
  • It reduces blood flow through the injured vessel
18
Q
  1. Outline what happens during platelet phase (phase 2) of primary haemostasis
A

Platelet adhesion
Platelet activation
Platelet aggregation

19
Q
  1. What happens during platelet adhesion
A

Platelets adhere to exposed collagen and themselves via platelet glycoprotein receptors

20
Q
  1. What does von Willebrand factor do
A

Encourages adherence to endothelium

21
Q
  1. What happens during platelet activation
A
  1. Platelets become activated and:
    • develop finger-like projections
    • release granule contents
  2. ADP, thromboxane A2 (TxA2) and thrombin activate more platelets
  3. Serotonin and TxA2 maintain vasoconstriction
22
Q
  1. What happens during platelet aggregation
A
  1. ADP makes platelets become sticky
  2. clotting factors are released
  3. Conformational change in the platelet receptor IIb/IIIa allows binding of fibrinogen which forms bridges between platelets
  4. The formed mass forms the platelet plug
23
Q
  1. What does the coagulation of blood depend on
A

depends on the balance between procoagulants and anticoagulants

24
Q
  1. When does coagulation occur
A

occurs when vessel injury initiates a chain reaction resulting in activation of clotting factors

25
Q
  1. What are clotting factors
A

Clotting factors are serum proteases

26
Q
  1. Explain how the common pathway works
A
  1. Activated Factor X combines with prothrombinase, Factor Va and calcium to convert prothrombin to thrombin
  2. Thrombin converts soluble fibrinogen into insoluble fibrin
  3. Factor XIIIa cross links the fibrin fibres and fibrin combines with calcium too to form a stable fibrin clot
27
Q
  1. Give features of the extrinsic pathway
A
  • Cascade of reactions involving factors that originate OUTSIDE of the blood
  • Triggered with tissue damage
  • FAST (~15 sec!)
28
Q
  1. Give features of the intrinsic pathway
A
  • Cascade of reactions involving factors that originate WITHIN the blood
  • Triggered when blood contacts with a negatively charged surface (e.g. glass, activated platelets)
  • Slow (1-6 mins)
29
Q
  1. Explain how the extrinsic pathway activates Factor X
A
  1. Peripheral tissues have membrane glycoprotein called Tissue Factor (thromboplastin)
  2. When the endothelium is damaged, Tissue Factor comes in contact with Factor VII, activating it.
  3. Factor VIIa, Tissue Factor and calcium combine to activate Factor X
30
Q
  1. Explain how the intrinsic pathway activates Factor X
A
  1. Factor XII is activated when blood comes in contact with negative charges (e.g glass, activated platelets, collagen)

2.activated platelets also release Platelet Factor 3

  1. Factor XIIa initiates a series of proteolytic steps that are calcium dependent which lead to the formation of Tenase complex
  2. This Tenase complex along with Platelet Factor 3 activates Factor X
31
Q
  1. What 4 clotting factors undergo post-translational modification when in the presence of the reduced form of Vitamin K
A

Factor:
- II (prothrombin)
- VII
- IX
- X

32
Q
  1. What does vitamin K reductase do
A

catalyses the conversion of vitamin K to its reduced form

33
Q
  1. How does warfarin lead to reduced clotting
A

inhibits vitamin K reductase which reduces the action of Factors II, VII, IX and X

34
Q
  1. Explain how clot retraction works to contribute to haemostasis
A
  1. Platelets attached to fibrin fibres contract
  2. This compresses the fibrin meshwork into a smaller mass
  3. As the clot retracts, it pulls the torn edges of the vessel closer together

Haematology (14 decks)

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