MLAB 1227: COAGULATIONKERI 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 NOTESEEN IN CONDITIONS WITH INCREASED NEED AND/OR DESTRUCTION

May Hegglin anomaly, Bernard-Soulier syndrome, pregnancy,

Giant platelets Micromegakaryocytes= Dwarf Megs

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.platelet-research.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.

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.platelet-research.org/1/function_hemo.htm.

REFERENCES