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🩸Hema🎀 > 3.1: Platelet ultrastructure > Flashcards

3.1: Platelet ultrastructure Flashcards

1
Q

Platelets are anatomically divided into four areas:

A
  1. Peripheral zone
  2. Sol-gel zone
  3. Organelle zone
  4. Membranous system
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2
Q

Peripheral Zone

A

Glycocalyx
Resting Platelet Membrane

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3
Q

Sol-gel Zone

A

Microtubules
Microfilaments

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4
Q

Organelle Zone

A

Alpha Granules
Dense Granules
Lysosomes

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5
Q

Membranous System

A

Dense Tubular System (DTS)
Surface-Connected Canalicular System (SCCS)

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6
Q

Outer surface, fuzzy coating primarily composed of glycoproteins

A

Glycocalyx

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7
Q

The platelet membrane surface that absorbs albumin, fibrinogen, and other plasma proteins

A

Glycocalyx

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8
Q

Resembles any biologic membrane bilayer composed of proteins and lipids

A

Resting Platelet Membrane

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9
Q

Predominant lipids of Resting Platelet Membrane

A

Phospholipids
Cholesterol

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10
Q

Predominant lipids of Resting Platelet Membrane:

forms the basic structure

A

Phospholipids

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11
Q

Predominant lipids of Resting Platelet Membrane:

distributed asymmetrically throughout the phospholipids

A

Cholesterol

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12
Q

Forms a bilayer with their polar heads oriented towards the aqueous environments (blood plasma - externally, cytoplasm - internally)

A

Phospholipids

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13
Q

Phospholipids:

predominant in the outer blood plasma layer

A

Neutral Phospholipids

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14
Q

Phospholipids:

predominant in the inner cytoplasmic layer

A

Anionic or Polar Phospholipids

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15
Q

Neutral Phospholipids:

A

● Phosphatidylcholine
● Sphingomyelin

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16
Q

Anionic or Polar Phospholipids:

A

● Phosphatidylinositol
● Phosphatidylethanolamine
● Phosphatidylserine

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17
Q

Anionic or Polar Phospholipids:

supplies arachidonic acid

A

Phosphatidylinositol

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18
Q

Anionic or Polar Phospholipids:

flips to the external surface and is responsible in the assembly of the coagulation factor complexes in the surface

A

Phosphatidylserine

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19
Q

Stabilizes the membrane, maintains fluidity, and helps you control the transmembranous passage of materials through the selectively permeable plasma membrane

A

Cholesterol

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20
Q

Maintains the platelet’s discoid shape

A

Microtubules

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21
Q

Parallel the plane of the outer surface of the platelet and reside just within, although not touching, the plasma membrane

A

Microtubules

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22
Q

Microtubules disassemble at refrigerator temp or when platelets are treated with

A

colchicine

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23
Q

Move inward on platelet activation to enable the expression of a-granule contents

A

Microtubules

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24
Q

Provide rigidity to pseudopods during platelet activation.

A

Microtubules

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25
Q

A thick meshwork that lies between the microtubules and the membrane

A

Microfilaments

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26
Q

Microfilaments is composed of

A

Actin

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27
Q

Is contractile in platelets and anchors in the plasma membrane glycoproteins and proteoglycans

A

Actin

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28
Q

Actin in resting platelet:

A

globular and amorphous

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29
Q

Actin With elevated cytoplasmic calcium:

A

filamentous and contractile

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30
Q

Ropelike polymers of desmin and vimentin

A

Intermediate Filaments

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31
Q

Connect with actin and the tubules, maintaining platelet shape

A

Intermediate Filaments

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32
Q

Stains medium-gray in osmium dye transmission electron microscopy preparations

A

Alpha Granules

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33
Q

Alpha Granules are filled with

A

proteins

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34
Q

Alpha granules fuse with _____ in activated platelets

A

SCCS (Surface-Connected Canalicular System)

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35
Q

Stain black (opaque) when treated with osmium in transmission electron microscopy

A

Dense Granules

36
Q

As platelets activate, these migrate to the plasma membrane and release their contents directly into the plasma

A

Dense Granules

37
Q

Dense Granules

A

Calcium
Adenosine diphosphate
Pyrophosphate/Phosphate
Adenosine triphosphate
Serotonin
Magnesium

38
Q

The contents of these probably digest vessel wall matrix components during in vivo aggregation and may also autophagic debris

A

Lysosomes

39
Q

Parallel and closely aligned to SCCS

A

Dense Tubular System (DTS)

40
Q

Are condensed remnant of the rough ER

A

Dense Tubular System (DTS)

41
Q

Sequesters calcium and bears a number of enzymes that support platelet activation

A

Dense Tubular System (DTS)

42
Q

“Control center” for platelet activation

A

Dense Tubular System (DTS)

43
Q

Formed by the plasma membrane invading the platelet inhibitor, it acts as a canal for the release of granules. Also involved in platelet phagocytosis

A

Surface-Connected Canalicular System (SCCS)

44
Q

Enables the platelet to store additional quantities of the same hemostatic proteins found on the glycocalyx

A

Surface-Connected Canalicular System (SCCS)

45
Q

Also enhances interaction of platelets with the environment

A

Surface-Connected Canalicular System (SCCS)

46
Q

It is this system that forms invaginated, sponge-like portion of the cell that provides an expanded reactive surface to which plasma clotting factors are selectively adsorbed

A

Surface-Connected Canalicular System (SCCS)

47
Q

Is the route for endocytosis and for secretion of alpha granule contents upon platelet activation

A

Surface-Connected Canalicular System (SCCS)

48
Q

Are heterodimeric (composed of two dissimilar proteins)

A

INTEGRINS

49
Q

Binds collagen and enables platelet to adhere to the injured blood vessel lining

A

INTEGRINS

50
Q

INTEGRINS:

A

GP Ia/IIa
a5β1 and a6β1
GP VI
GP IV

51
Q

Is an integrin that binds the subendothelial collagen that becomes exposed in the damaged blood vessel wall, promoting adhesion of the platelet to the vessel wall

A

GP Ia/IIa

52
Q

Member of the immunoglobulin gene family

A

GP VI

53
Q

A key collagen receptor that also binds the adhesive protein thrombospondin

A

GP IV

54
Q

Is a leucine-rich repeat family CAM

A

GP Ib/IX/V

55
Q

GP Ib/IX/V:

Bind to vWF and support platelet tethering (deceleration)

A

GP Ibα molecules

56
Q

GP Ib/IX/V:

Cross the platelet membrane and interact with actin-binding protein to provide outside-in signaling

A

GP Ibβ molecules

57
Q

GP Ib/IX/V:

Help assemble the four GP Ib

A

GP IX & GP V

58
Q

Are in a low affinity conformation as they are distributed across the plasma membrane, the SCCS, and the internal layer of the alpha granule membranes of resting platelets

A

GP IIb/IIIa

59
Q

Ligand for a2β1

A

Collagen

60
Q

Ligand for avβ1

A

Vitronectin

61
Q

Ligand for a5β1

A

Laminin

62
Q

Ligand for a6β1

A

Fibronectin

63
Q

Ligand for GP VI

A

Collagen

64
Q

Ligand for GP IIb/IIIa or integrin aIIbβ3

A

Fibrinogen and vWF

65
Q

Cleaved by thrombin

A

PAR1 and PAR4

66
Q

also interacts with platelets by binding or digesting two CAMs in the leucine-rich repeat family, GP Ibα and GP V

A

Thrombin

67
Q

Ligand: ADP

A

P2Y1 and P2Y12

68
Q

Are linked to different G-proteins and produce distinct intracellular signals that have complementary effects on platelet aggregation

A

P2Y1 and P2Y12

69
Q

Cleavage of either of the two receptors activates the platelet through G-proteins that in turn activate at least two internal physiologic pathways

A

PAR1 and PAR4

70
Q

Leads to an increase in intracellular calcium levels and contributes to initial platelet activation, shape change, and the formation of small reversible aggregates

A

P2Y1

71
Q

Leads to a decrease in cyclic adenosine monophosphate
(cAMP) levels and supports the formation of irreversible platelet aggregates

A

P2Y12

72
Q

Ligand: Thromboxane A2

A

TPα and TPβ

73
Q

The ligand-receptor interaction produces more TXA2 from the platelet, a G-protein-based autocrine system that activates neighboring platelets

A

TPα and TPβ

74
Q

Ligand: Epinephrine

A

α2-adrenergic

75
Q

Opens membrane calcium channels

A

α2-adrenergic

76
Q

Ligand: Prostacyclin

A

Inositol Triphosphate

77
Q

Membrane receptor-ligand binding results in an increase in the internal cAMP concentration of the platelet and an inhibition of platelet activation

A

Inositol Triphosphate

78
Q

Additional Membrane Receptors:

CAM immunoglobulin family

A

ICAMs (CD50, CD54, CD102)
PECAMs (CD31)
FcyIIA (CD32)

79
Q

Additional Membrane Receptors:

CAM selectin family

A

P-selectin (CD62)

80
Q

Additional Membrane Receptors:

Plays a role in inflammation and the immune reaction

A

ICAMs (CD50, CD54, CD102)

81
Q

Additional Membrane Receptors:

Mediates platelet-white blood cell and platelet-endothelial cell adhesion

A

PECAMs (CD31)

82
Q

Additional Membrane Receptors:

A low-affinity receptor for the immunoglobulin Fc portion

A

FcyIIA (CD32)

83
Q

Additional Membrane Receptors:

An integrin that facilitates platelet binding to endothelial cells, leukocytes, and one another

A

P-selectin
(CD62)

84
Q

Additional Membrane Receptors:

Found on the alpha granule membranes of the resting platelet but migrates via the SCCS to the surface of activated platelets

A

P-selectin
(CD62)

85
Q
A

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