MLAB 1227:
COAGULATION
KERI BROPHY-MARTINEZ
The Platelets
ALL ABOUT PLATELETS…

Second major component of the hemostatic
system
PLATELETS
 What






is a platelet?
Small 2-3 µm
Disc-shaped
Anuclear
Reddish-purple granules
Fragments of
megakaryocyte cytoplasm
Surface has a sponge-like
look, openings are channels
that extend deep within
cell
PLATELETS

Life span


7-10 days
Reference Range

150-450 x 109 /L
PLATELET: SIDE NOTE
SEEN IN CONDITIONS WITH INCREASED NEED AND/OR DESTRUCTION


Giant platelets
May Hegglin anomaly, BernardSoulier syndrome, pregnancy,
 Micromegakaryocytes=
Megs
Dwarf
ANATOMY

OF A
PLATELET
Divided into 4 zones
Peripheral
 Structural
 Organelle
 Membrane

PERIPHERAL

ZONE:
Responsible for platelet adhesion and aggregation
Glycocalyx: Fluffy surface coat
 Contains glycoprotein receptors:
 GPIb binds von Willebrand’s factor needed for platelet
adhesion to collagen
 GPIIb/IIIa binds fibrinogen needed for aggregation
 Bind ADP and thrombin, promoting aggregation
 Factors I, V, VIII on surface, involved in 2o hemostasis
 Membrane:
 Exposed on platelet activation
 Layer called PF3 (platelet factor) surface for interaction of
plasma coagulation factors
 Initiation of formation of thromboxane A2. This stimulates
aggregation and vasoconstriction

STRUCTURAL/

SO-GEL ZONE
Responsible for platelet retraction/contraction
functions and platelet shape
◦ Microtubules/Microfilaments
◦ Cytoskeleton
◦ Binding proteins
◦ Actin
◦ Myosin
ORGANELLE ZONE

Responsible for storage and platelet release
functions
◦ Granules
 Dense bodies, alpha granules, lysosomal
granules and microperoxisomes
◦ Mitochondria
◦ Glycogen
MEMBRANE ZONE

Responsible for secretion of granule contents
and storage of calcium

Two systems
Surface-connected open canalicular system (OCS)
 Dense tubular system(DTS)

ANATOMY

OF A
PLATELET
http://www.plateletresearch.org/1/function_morpho.htm#
PRODUCTION
OF
PLATELETS
Made in Bone marrow
 Need dictates the amount of platelets produced.
 Stimulus for production is the platelet mass in
circulating blood ~ 80 % and megakaryocyte
mass in bone marrow
 Originate from CFU-GEMM to form CFU-Meg
 Cytokines and growth factors such as IL-3 and
GM-CSF influences progenitor stages

PLATELET DEVELOPMENT


Megakaryoblast
 10-15 µm
 Increased nuclear: cytoplasmic
ratio
Promegakaryocyte
 80 µm
 Dense alpha and lysosomal
granules

Basophilic megakaryocyte

Megakaryocyte
PRODUCTION



OF
PLATELETS
Precursor Cell=
Megakaryocyte
Produces about 2000
platelets
Platelets are released via
sinuses of bone marrow
 2/3 pb
 1/3 sequestered in spleen
PRODUCTION

OF
PLATELETS
Thrombopoietin (TPO)

Regulates platelet development

Influences all stages of megakaryocyte production

Produced in the liver, kidney and spleen
PRODUCTION

OF
PLATELETS
How does TPO work?


Maintains a constant number of platelets in
peripheral blood by binding Mpl (platelet receptor).
Bound TPO can not stimulate proliferation of bone
marrow progenitor cells
The higher the platelet count, the more TPO is
bound and stimulation of bone marrow is decreased.
REFERENCES
McKenzie, Shirlyn B., and J. Lynne. Williams.
"Chapter 29." Clinical Laboratory Hematology.
Boston: Pearson, 2010. Print.
 Platelet Research Laboratories. Platelet
Function. Retrieved from http://www.plateletresearch.org/1/function_hemo.htm.
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