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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