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Haemostasis & Thrombosis > Platelets and Megakaryocytes > Flashcards

Platelets and Megakaryocytes Flashcards

1
Q

What is the minimal required number of platelets to prevent spontaneous bleeding & maintain endothelial integrity?

A

> 5,000/uL

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2
Q

What are 5 characteristics of platelets?

A

Mitochondria
no nucleus
open surface connected canalicular system
dense tubular system
granules

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3
Q

What 2 types of RNA is found in platelets?

A

mRNA
miRNA (regulatory role)

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4
Q

What are 2 sources of proteins for platelets?

A

from megakaryocytes
endocytosis

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5
Q

What is the most abundant granule type in platelets?

A

Alpha

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6
Q

What do alpha granules contain?

A

different proteins
coagulation factors (VWF or Factor V)
growth factors

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7
Q

What is the open surface connected canalicular system?

A

Internal membrane that is continuous with the plasma membrane

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8
Q

What does the release of alpha granules cause?

A

generates a complex microenvironment that is important for
Haemostasis
inflammation
wound healing

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9
Q

What do dense granules contain?

A

Ca2+
serotonin
ADP/ATP/GDP/GTP
-vely charged phosphates

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10
Q

What do platelet lysosomes contain?

A

Hydrolases

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11
Q

What are platelets generated through?

A

Fragmentation of cytoplasm of giant bone marrow cells called megakaryocytes

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12
Q

What are MKs derived from?

A

Haematopoietic stem cells (HSCs)

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13
Q

What drives the development of MKs from HSCs?

A

THrombopoietin

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14
Q

What is the process MKs develop by?

A

endomitosis

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15
Q

What is endomitosis?

A

Nuclear DNA is duplicated but cell does not divide
MK keeps polypoid nucleus (16N)
MK cytoplasm is remodeled into proplatelets
distal constrictions break off new platelets

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16
Q

What is CD41?

A

Integrin proteins made of 2 chains that is needed for platelet aggregation

17
Q

What are demarcation membranes?

A

Precursor of membranes for future platelets (plasma membrane and OCS) that is connected to plasma membrane

18
Q

What 2 things are proplatelet formation dependent on?

A

Microtubules
Actin filaments

19
Q

What are formed at proplatelet tips?

A

Nascent platelets loaded with granules

20
Q

What do microtubules do in proplatelets?

A

Mediate transport of granules from MK cell body to proplatelet tip

21
Q

What accelerates platelet release?

A

Shear forces from blood flow (limiting factor)

22
Q

Where are immature MKs located and where do they go during maturation?

A

Start at osteoblastic niche of bone marrow & migrate to subendothelium of venous sinusoids

23
Q

What is another site other than bone marrow that platelet formation can occur?

A

Lung capilllaries

24
Q
A

Haemostasis & Thrombosis (17 decks)

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