platelets

what are platelets produced from / what is thei precursor cell

megakaryocytes

distribution of platelets

• 30% spleen

• 70% peripheral blood

platelet reference range

150,000 ti 400,000/mm3

life span of platelets

9-12 days

first function of platelets

initial arrest of bleeding and formation of platelet plug

2 parts of step 1 (stopping bleed + platelet plug)

a) adhesion

b) aggregation

what occurs in adhesion

• glycoprotein Ib binds to exposed collagen

• requires vWf

• release/secretion of ADP + granule components (factor V and fibrinogen)

what binds to exposed collagen

glycoprotein Ib

what does adhesion require

vWf

what does adhesion result in (secreting)?

ADP + other granule components

what are other granule components that are secreted with ADP in adhesion

factor V and fibrinogen

what occurs in aggregation

• ADP stimulates platelets to undergo shape change

  • exposes glycoprotein IIb/IIIa complex that binds to fibrinogen

• fibrinogen binding links platelets (= 1st + reversible phase of aggregation)

• strong stimuli cause aggregating platelets to secrete (→ irreversible aggregation)

what is the first step of aggregation

fibrinogen binding to glycoprotein IIb/IIIa complex links the platelets

which step of aggregation is reversible

the first step

which step of aggregation is irreversible

second step

describe the reversible step of aggregation

1st step - fibrinogen linking platelets

describe the irreversible step of aggregation

strong stimuli causing aggregating platelets to secrete/release

how can the first step of aggregation be reversed

weak stimuli to aggregating platelets causing disassociation

what lab method tests the platelets’ ability to properly adhere and aggregate at the injury site

PFA test

what is built at the injury site after adhesion and aggregation

a platelet plug

what is the 2nd function of platelets

localization of platelet plug

how are platelets localized

• secreting platelets release arachidonic acid which becomes prostaglandin in the platelet

• arachidonic acid is processed by adjacent endothelial cells to form platelet-inhibiting prostacyclin

what do the secreting platelets release and what does it become inside th platelet

arachidonic acid, prostaglandin

what will prostaglandin later become

thromboxane A2

how is platelet-inhibiting prostacyclin formed

arachidonic acid is processed by adjacent endothelial cells

platelet’s third function

asembly and localization of platelet plug

platelet release components

fibrinogen, factor VIII, factor V

when is fibrinogen bound on the platelet surface

aggregation

how is factor VIII bound on the platelet surface

with vWf

what is bound on the platelet surface

fibrinogen and factor VIII

what occurs in the assembly and localization of platelet plug

shape change exposes platelet membrane phospholipid (PL)

• binds Factor VIII and IXa complex

• binds factor V and Xa complex

what does the binding of factor VIII and IXa require

Ca++

what does the binding of Factor V and Xa require

Ca++

what was the platelet phospholipid membrane historically called

platelet factor 3