- serotonin - TXA2 - endothelin-1

1) Platelet structure & function Flashcards by Samantha Boyer

2 functions of hemostasis

stop bleeding
maintain blood in fluid form

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breakdown of a clot

fibrinolysis

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function of plasmin

digests fibrinogen & fibrin (fibrinolysis)

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pinpoint bleeding from arterioles, venules

petechiae

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bruises/bleeding from veins

ecchymoses

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nosebleed

epistaxis

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mucocutaneous bleeding

platelets deficient or defective

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joint bleeding

factor deficiency

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presents with both mucocutaneous bleeding and joint bleeding

DIC

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clot formation on the interior of an intact vessel

thrombosis

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the ———– effect is disturbed when there is stagnation of blood flow

endothelial anticoagulant

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normal VECs are ————–, so clots do not form

thromboresistant

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inactive coag proteins in circulation

zymogens

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VECs, plasma components and platelets normally repel each other because…

they are negatively charged

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vasoconstrictors

serotonin
TXA2
endothelin-1

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vasodilator

prostaglandin (PGI2)

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tissue factor is also called…

thromboplastin

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t-PA

tissue plasminogen activator

dissolves fibrin clot

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inactivates and clears thrombin
activates protein C coag inhibitor

thrombomodulin

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clots mainly form in…

arterioles & venules

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for normal function, need at least —— plt

100

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plt <20

at risk for spontaneous bleed

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plt >20, <50

at risk for hemorrhage during surgery, trauma

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plt >50, <100

minimal risk of hemorrhage during surgery

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platelets have ----------- (nonspecific) granules

azurophilic

platelets last...

7-10 days

distribution of platelets in body

70% in circulation 30% in spleen reserves

splenomegaly --- plt in PB

↓

stages of plt development

- HSC - CFU-GEMM - CFU-Meg - BFU-Meg - Megakaryoblast - Promegakaryocyte - (Meta)megakaryocyte - Platelet

regulates all stages of plt development

thrombopoietin (TPO)

TPO is made by the...

liver spleen kidneys

TPO binds to ------- on plts/megas, which renders it unable to stimulate proliferation (negative feedback)

CD110

DNA count doubles but there is no cell division results in polyploidy cells

endomitosis megakaryocytes

DMS

demarcation membrane system membranes form all throughout mega cytoplasm, which will become platelets

blast → mature plt takes --- days

characteristics of megakaryoblast

- 20-45 μm - single round or oval nucleus - 1-2 nucleoli - blunt protrusions (blebs) - scant cytoplasm - no granules

characteristics of promegakaryocyte

- more cytoplasm - multiple nuclei - 20-80 μm - reddish granules - demarcation membranes begin to form

characteristics of megakaryocyte

- multiple nuclei - 30-100 μm - many small uniform granules, reddish blue - demarcation system

what happens once the mega reaches maturity and is ready to produce plts?

membrane ruptures nuclei are engulfed by macrophages

RR for megas on BM

1-4 megas/100 nucleated cells

plt shape at rest

discoid

4 plt zones

- peripheral zone - structural zone - organelle zone - membrane systems

parts of plt peripheral zone

glycocalyx (GPs) phospholipid membrane

vWF, thrombin and ristocetin receptor

GPIb/IX

CD42b/c

GPIb/IX

fibrinogen receptor

GPIIb/IIIa

hidden in resting plts and appears on activation

GPIIb/IIIa

CD41/61

GPIIb/IIIa

parts of plt structural zone

- cytoskeleton - microtubules - protein network

function of plt microtubules

contract during stimulation allows for degranulation, and ↑ surface area

plt protein network consists of...

actin and myosin

parts of plt organelle zone

- mitochondria - glycogen (source of energy) - granules

3 types of plt granules

- dense bodies - alpha granules - lysosomal granules

contained in dense bodies

ADP ATP serotonin Ca2+

contained in alpha granules

PF4 PDGF

(alpha granules/dense bodies) are more numerous

alpha granules

contained in plt lysosomal granules

microbicidal enzymes proteases hydrolases

OCS

open cannalicular system

2 plt membrane systems

- OCS - DTS

function of OCS

- from surface to interior - plt storage and secretion

DTS

dense tubular system

function of DTS

Ca2+ storage

Bernard-Soulier disease

↓ or dysfunctional GPIb/IX

2 types of plt adhesion problems

Bernard-Soulier disease von Willebrand disease

activation of plt leads to externalization of --------- and ...

GPIIb/IIIa secretion of granules' contents

precursor to TXA2

arachidonic acid

TXA2 synthesis requires enzyme ---------- causes...

cyclooxygenase degranulation & vasoconstriction

action of aspirin

inhibits TXA2 synthesis

most potent plt activator

thrombin

2 types of plt aggregation problems

Glanzmann thrombasthenia ↓ fibrinogen

Glanzmann thrombasthenia

↓ or dysfunctional GPIIb/IIIa

hepatin neutralizer

PF4

promotes smooth muscle growth helps heal wounded tissue

PDGF