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Hemostasis > Sections 1 and 2: Platelet Function > Flashcards

Sections 1 and 2: Platelet Function Flashcards

1
Q

Hemostasis definition

A

Process of blood clotting to arrest bleeding and re-establishment of blood flow during the healing process

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2
Q

Hemostasis involved parameters

A
  • vascular
  • platelets
  • fibrin clot formation- coag cascade
  • control (inhibitory systems)
  • fibrinolysis
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3
Q

Abnormal bleeding vs abnormal clotting

A

hemorrhage and thrombosis

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4
Q

Primary hemostasis

A
  • Platelet aggregation (form platelet plug)
  • Capillaries
  • White thrombus forms
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5
Q

Secondary hemostasis

A
  • Fibrin strands form to strengthen platelet plug and RBCs get caught in mesh
  • Arteries/bigger vessels
  • Red thrombus
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6
Q

Fibrinolysis

A

Dissolves blood clots (initiation of wound healing)

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7
Q

Hemarthralgia

A

Bleeding in joints

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8
Q

Medical terms that mean bruise

A
  • Purpura
  • Ecchymoses
  • Hematoma
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9
Q

Epistaxis

A

Nose bleed

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10
Q

List the 3 vascular layers from inside to outside

A
  1. Tunica intima
  2. Tunica media
  3. Tunica adventia
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11
Q

Tunica intima

A

Layers of broad flat endothelial cells with underlying basement membrane - collagen

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12
Q

Tunica media

A
  • Elastic tissue and smooth muscle
  • Controls vasoconstriction and sometimes vasodilation
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13
Q

Tunica adventia

A

Connective tissue support

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14
Q

How does the vasculature prevent thrombus formation in hemostasis?

A
  • Provides physical barrier of endothelial cells covering basement membrane to prevent blood, platelets, and clotting factors from sticking
  • Endothelial cells generate PGI2 (Prostacylin) and nitric oxide, which causes vasodilation and inhibits platelet adhesion to those cells
  • Vasculature involved in activity of Protein C (thrombomodulin) and anti-thrombin (heparan)
  • Tissue factor pathway inhibitor (TFPI) inhibits Tissue Factor/Factor VIIa complex
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15
Q

List steps of general hemostasis when endothelial lining is disrupted

A
  1. Vasoconstriction
  2. Initial stimuli of hemostasis
  3. Localize clot formation
  4. Provide activators for clearance of thrombus to break down fibrin clot
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16
Q

Explain the first step of hemostasis, vasoconstriction

A
  • Blood flow slows such that platelets and coag factors easily attach to site of injury
  • Shear stress pushes platelets to vessel periphery (injury site)
17
Q

Explain the second step of hemostasis: initial stimuli

A
  • Damaged endothelial cells release platelet activating factor (PAF) to activate even more platelets
  • Tissue Factor III released (present in all tissues)
  • Collagen is exposed such that platelets adhere to it
18
Q

Explain the third step of hemostasis: localize clot formation

A
  • Endothelial cells synthesize and release von Willebrands factor for platelet adhesion, as well as secrete ADAMTS13 to chop up vWF
  • Binding sites for coag factors IXa and Xa
19
Q

Explain the fourth step of hemostasis: provide activators for clearance of thrombus to break down fibrin clot

A
  • ECs secrete tissue plasminogen activator to facilitate clot breakdown
20
Q

Fill in the blank
ECs play a role in _________, ________, and _______ of the clot

A

formation, prevention, breakdown

21
Q

Thrombopoietin (TPO) function

A
  • Regulates megakaryocyte production and platelet release from the BM in response to thrombocytopenia
  • Inhibits megakaryocyte apoptosis
  • Binds receptors on circulating platelets and BM megakaryocytes, gets internalized, and degraded
22
Q

Explain how TPO levels relate to platelet levels

A
  • More platelets means less TPO (gets destroyed), so fewer megakaryocytes
  • Fewer platelets means more TPO, so more megakaryocytes
23
Q

Adhesion

A

Platelets stick to site of injury (exposed collagen)

24
Q

Aggregation

A

Platelets stick to other platelets (helps close physical gap)

25
Platelet glycocalyx
- Outer layer (peripheral zone) - Mediates platelet adhesion and aggregation
26
Platelet open canalicular system
- Peripheral zone, extension of platelet membrane - Channels of membrane wind into platelet so that stuff moves in and out
27
Platelet cytoskeleton
- Sol-gel zone - Helps secretion process and structural integrity - Microfilaments made of actin and myosin
28
Platelet dense tubule system
- Sol-gel zone - Plt activation and calcium storage/release
29
Platelet dense granules
- 6 per plt - ADP, calcium, serotonin....etc
30
Platelet alpha granules
- ~55 per plt, more numerous than dense granules and give visual texture on Wright stain - TXA2, vWF, FV, FVIII, FI, HMWK, PF4, plasminogen, PAI-1...etc)
31
Explain how aspirin prevents plt activation/aggregation
Aspirin inhibits cyclooxygenase-1 such that thromboxane A2 can't be formed
32
Explain how a platelet adheres to collagen
- Platelets can't directly stick to collagen, so use vWF as intermediate glue - vWF binds GP1b receptor on plt
33
List steps of primary hemostasis
1. Platelet adhesion 2. Shape change 3. Plt aggregation 4. Secretion 5. Primary hemostatic plug formed
34
Explain the process of platelet activation from start to finish of clot
1. Plt adheres to collagen via vWF binding GP1b receptor 2. Adhesion initiates a shape change to allow granular content secretion (serotonin, vWF, ADP...etc) 4. Plts aggregate via ADP and TXA2 5. Fibrinogen attaches to platelet membrane forming bridges between platelets resulting in a platelet plug (GPIIb/IIIa) 6. Actin and myosin contract to pull clot in tight and stop bleeding 7. Platelet plug gives foundation for clot formation
35
Explain process of platelet shape change
1. Agonist (collagen/PAF) 2. Pseudopods develop on plt surface that contain actin and myosin 3. Microtubule circumferential ring contracts 4. Membrane phospholipids activated 5. Glycoprotein IIb/IIIa receptors appear 6. Internal biochemical changes occur 7. Granule secretion
36
List granule contents and their roles
- Serotonin = vasoconstriction - vWF = plt adhesion - ADP and TXA2 = plt aggregation - Calcium = plt activation/coag cascade - Fibrinogen = plt aggreg/coag cascade
37
How do ADP and TXA2 facilitate plt aggregation?
They expose the GPIIb and IIIa complex, which enables fibrinogen to come bind and crosslink plts for aggregation
38
Explain how platelet plug formation provides foundation for clot formation
Platelet Factor III (PF3) moves to outer surface of plt membrane to provide binding site for Vitamin K-dependent factors to support coag cascade
39
What is Platelet Factor 3?
It's the whole entire primary hemostatic complex! It provides a phospholipid-rich surface to support the coag cascade

Hemostasis (10 decks)

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