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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
A thick meshwork that lies between the microtubules and the membrane
Microfilaments
26
Microfilaments is composed of
Actin
27
Is contractile in platelets and anchors in the plasma membrane glycoproteins and proteoglycans
Actin
28
Actin in resting platelet:
globular and amorphous
29
Actin With elevated cytoplasmic calcium:
filamentous and contractile
30
Ropelike polymers of desmin and vimentin
Intermediate Filaments
31
Connect with actin and the tubules, maintaining platelet shape
Intermediate Filaments
32
Stains medium-gray in osmium dye transmission electron microscopy preparations
Alpha Granules
33
Alpha Granules are filled with
proteins
34
Alpha granules fuse with _____ in activated platelets
SCCS (Surface-Connected Canalicular System)
35
Stain black (opaque) when treated with osmium in transmission electron microscopy
Dense Granules
36
As platelets activate, these migrate to the plasma membrane and release their contents directly into the plasma
Dense Granules
37
Dense Granules
Calcium Adenosine diphosphate Pyrophosphate/Phosphate Adenosine triphosphate Serotonin Magnesium
38
The contents of these probably digest vessel wall matrix components during in vivo aggregation and may also autophagic debris
Lysosomes
39
Parallel and closely aligned to SCCS
Dense Tubular System (DTS)
40
Are condensed remnant of the rough ER
Dense Tubular System (DTS)
41
Sequesters calcium and bears a number of enzymes that support platelet activation
Dense Tubular System (DTS)
42
“Control center” for platelet activation
Dense Tubular System (DTS)
43
Formed by the plasma membrane invading the platelet inhibitor, it acts as a canal for the release of granules. Also involved in platelet phagocytosis
Surface-Connected Canalicular System (SCCS)
44
Enables the platelet to store additional quantities of the same hemostatic proteins found on the glycocalyx
Surface-Connected Canalicular System (SCCS)
45
Also enhances interaction of platelets with the environment
Surface-Connected Canalicular System (SCCS)
46
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
Surface-Connected Canalicular System (SCCS)
47
Is the route for endocytosis and for secretion of alpha granule contents upon platelet activation
Surface-Connected Canalicular System (SCCS)
48
Are heterodimeric (composed of two dissimilar proteins)
INTEGRINS
49
Binds collagen and enables platelet to adhere to the injured blood vessel lining
INTEGRINS
50
INTEGRINS:
GP Ia/IIa a5β1 and a6β1 GP VI GP IV
51
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
GP Ia/IIa
52
Member of the immunoglobulin gene family
GP VI
53
A key collagen receptor that also binds the adhesive protein thrombospondin
GP IV
54
Is a leucine-rich repeat family CAM
GP Ib/IX/V
55
GP Ib/IX/V: Bind to vWF and support platelet tethering (deceleration)
GP Ibα molecules
56
GP Ib/IX/V: Cross the platelet membrane and interact with actin-binding protein to provide outside-in signaling
GP Ibβ molecules
57
GP Ib/IX/V: Help assemble the four GP Ib
GP IX & GP V
58
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
GP IIb/IIIa
59
Ligand for a2β1
Collagen
60
Ligand for avβ1
Vitronectin
61
Ligand for a5β1
Laminin
62
Ligand for a6β1
Fibronectin
63
Ligand for GP VI
Collagen
64
Ligand for GP IIb/IIIa or integrin aIIbβ3
Fibrinogen and vWF
65
Cleaved by thrombin
PAR1 and PAR4
66
also interacts with platelets by binding or digesting two CAMs in the leucine-rich repeat family, GP Ibα and GP V
Thrombin
67
Ligand: ADP
P2Y1 and P2Y12
68
Are linked to different G-proteins and produce distinct intracellular signals that have complementary effects on platelet aggregation
P2Y1 and P2Y12
69
Cleavage of either of the two receptors activates the platelet through G-proteins that in turn activate at least two internal physiologic pathways
PAR1 and PAR4
70
Leads to an increase in intracellular calcium levels and contributes to initial platelet activation, shape change, and the formation of small reversible aggregates
P2Y1
71
Leads to a decrease in cyclic adenosine monophosphate (cAMP) levels and supports the formation of irreversible platelet aggregates
P2Y12
72
Ligand: Thromboxane A2
TPα and TPβ
73
The ligand-receptor interaction produces more TXA2 from the platelet, a G-protein-based autocrine system that activates neighboring platelets
TPα and TPβ
74
Ligand: Epinephrine
α2-adrenergic
75
Opens membrane calcium channels
α2-adrenergic
76
Ligand: Prostacyclin
Inositol Triphosphate
77
Membrane receptor-ligand binding results in an increase in the internal cAMP concentration of the platelet and an inhibition of platelet activation
Inositol Triphosphate
78
Additional Membrane Receptors: CAM immunoglobulin family
ICAMs (CD50, CD54, CD102) PECAMs (CD31) FcyIIA (CD32)
79
Additional Membrane Receptors: CAM selectin family
P-selectin (CD62)
80
Additional Membrane Receptors: Plays a role in inflammation and the immune reaction
ICAMs (CD50, CD54, CD102)
81
Additional Membrane Receptors: Mediates platelet-white blood cell and platelet-endothelial cell adhesion
PECAMs (CD31)
82
Additional Membrane Receptors: A low-affinity receptor for the immunoglobulin Fc portion
FcyIIA (CD32)
83
Additional Membrane Receptors: An integrin that facilitates platelet binding to endothelial cells, leukocytes, and one another
P-selectin (CD62)
84
Additional Membrane Receptors: Found on the alpha granule membranes of the resting platelet but migrates via the SCCS to the surface of activated platelets
P-selectin (CD62)
85

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