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Zlotnik- Blood Physiology > Platelets, Platelet Disorders > Flashcards

Platelets, Platelet Disorders Flashcards

1
Q

hemostasis

A

prevention of blood loss

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2
Q

4 mechanisms of hemostasis

A

1) vascular Constriction
2) Formation of Platelet Plug
3) Formation of a blood clot (coagulation)
4) growth of fibrous tissue to close a vessel hole permanently

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3
Q

Vasoconstriction

A
  • contractile response of vascular smooth muscle
    •Sensory impulses from traumatized vessel
    •Stimulation of smooth muscle via perivascular nerves results in spasm
    •Thromboxane A2 released from platelet dense granules
    •May be sufficient to close arterioles and small arteries
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4
Q

thrombus

A

stable clot

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5
Q

primary hemostasis

A

platelet aggregation
-vessel injury -> platelet adherence -> activation -> hemostatic plug
(within seconds)

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6
Q

secondary hemostasis

A

blood coagulation
-hemostatic plug ->fibrin strands -> thrombus -> clot contraction
(minutes-hours)

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7
Q

thrombopoiesis

A

CFU-Meg->Megakaryocyte->thrombocyte

-IL3, thrombopoietin, GM-CSF, SCF

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8
Q

megakaryocyte

A
  • giant cells with multiple copies of DNA in nucleus

- edges break off to form platelets

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9
Q

platelets

A

-2-4micrometres in diameter
-lack nuclei -> can’t synthesize new proteins
-live ~10days -> drug consequences
-old plateletes are removed by macrophages in the spleen
aka thrombocytes
-mostly circulate in blood, some stored in spleen
-150,000-400,00/microliter of blood

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10
Q

hyalomere

A

outside concentric zone of platelet; microtubules maintain shape and contraction

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11
Q

granulomere

A

inside concentric zone of platelet; 3 types of granules (release prohemostatic and anti-hemostatic substances); few mitochondria

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12
Q

platelet adhesion

A
  • at site of endothelial injury

- mediated by integrins (GlycoProtein receptors)

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13
Q

integrins

A

integral membrane receptor proteins
aka GlycoProtein receptors
-receptor binding activates platelets

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14
Q

GP lalla

A

GlycoProtein receptor, binds collagen beneath the vascular bed

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15
Q

GP IbIX

A

GlycoProtein receptors, binds von willebrand factor on extra-vascular smooth muscle cells

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16
Q

activated platelets

A
  • change shape (spherical -> stellate) and discharge granule contents
  • serotonin-> local vasoconstriction
  • ADP -> activates other platelets -> amplification
  • adhesion activates phospholipase A2 in platelet membrane _> activates other platelets
  • activation exposes GP IIbIIIa receptors ->aggregation
17
Q

phospholipase A2

A

in platelet membrane -> activates other platelets -> amplification

18
Q

aspirin

A
  • inhibits platelet activation and aggregation

- irreversible inhibitor of cyclooxygenase enzymes (COX-1)

19
Q

NSAIDS

A
  • non-steroidal anti-inflammatory drugs (e.g. ibuprofen)

- reversible COX inhibitors

20
Q

acetaminophen

A
  • tylenol/ paracetamol

- elevated transaminase indicates liver toxicity

21
Q

platelet aggregation

A
  • Mediated by fibrinogen receptors (GP IIbIIIa)

* GP IIbIIIa receptors become exposed during activation

22
Q

Bernard-Soulier syndrome

A

-defective vWf receptor (GPIb-IX) -> inactive platelets

23
Q

Glanzmann’s disease

A

defective fibrinogen receptor (GPIIb-IIIa) -> no aggregation

24
Q

antagonists for thrombosis

A

Abciximab and Eptifibatide bind to GPIIbIIIa and compete with fibrinogen.They prevent platelet aggregation

25
Q

plavix

A

binds/blocks ADP-receptor preventing ADP-activation

aka Clopidogrel

26
Q

Thrombocytopenia

A

decrease in platelets; < 150,000/ μl of blood

  • purpura, petechia, hemorrhage
  • positive tourniquet test is >20 petechiae in area of 3cm diameter of cubital fossa
  • increases bleeding time (normal is 2-6min)
27
Q

purpura

A

bleeding under the skin causing a purple or red discoloration)

28
Q

petechiae

A

minor bleeds under skin),

29
Q

Primary thrombocytopenic purpura

A

unknown cause

30
Q

Secondary thrombocytopenic purpura:

A

due to a known cause: aspirin overdose, aplastic anemia, malignancies infiltrating BM, infections like dengue fever (hemorrhagic fever).

31
Q

thrombocytosis

A
  • increase in platelets: >400,000 / μl of blood
  • thrombotic (clotting) events- stroke, heart attacks, pulmonary embolism
  • may happen after splenectomy bc fewer platelets are removed from circulation
  • gangrene
32
Q

eptifibatide

A
  • protein in rattlesnake

- inhibits GPIIbIIIa -> decrease in aggregation

33
Q

GPIIbIIIa

A

fibrinogen receptor, normally hidden but get exposed when platelets are activated

34
Q

thromboxane A2

A

produced by activated platelets and has prothrombotic properties

Zlotnik- Blood Physiology (5 decks)

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