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Platelets or thrombocytes are small
colorless, non nucleated cells.
With numerous cytoplasmic granules
Shape is spherical or rod shaped and
become oval or disc shaped when
inactivated.
Size: 1 to 4 micrometers in diameter.
Normal life span 8-12 days
Structure:
Cell membrane
Microtubule
Cytoplasm
It is 6 nm thick
(phospholipids, cholesterol and glycolipids),Carbohydrates(glycocalyx), Proteins and glycoproteins
Platelets surface is negatively charged
Sialic acid gives negative charge
Receptors on platelets surface –collagen , ADP,vWF,fibrinogen
Surface canalicular system
Platelets has prominent cytoskeleton
Microtubule
microfilament
Golgi apparatus
Endoplasmic reticulum
Mitochondria
Microtubule
Micro vesicles
Microfilaments
Granules
Proteins
Enzymes
Hormones.
Chemical substances
The major proteins present are contractile
proteins which are responsible for the
contraction of platelets:
Actin
Myosin
Thrombosthenin
Fibrin-stabilizing factor…. Clotting factor
Platelet derived growth factor (PDGF)
............. helps repair damaged vascular
walls.
Von willibrand factor
Alpha granules
Dense granules
The enzymes present are adenosine
triphosphatase and the enzymes
necessary for the synthesis of prostaglandin
Destroyed in spleen
Life span 8-12 days
Adhesiveness
Aggregation
Agglutination
Role In haemostasis - vasoconstiction
platelet plug formation
Role in clot formation
Role in clot retraction
Role in repair of injured blood vessels
Role in immunity
Transport and storage functions
Normal count – 1.5 – 4.5 lac/cubic mm
Physiological variation age , sex, food,
exercise , altitude
Variation with disease
Thrombocytosis
Thrombocytopenia
After splenctomy
After severe injury , hemorrhage , major
surgery
Blood cancers like CML , myelofibrosis
Idiopathic thrombocytopenic purpura
Bone marrow depression due to drugs ,
radiation
Hypersplenism
Infections like dengue , chicken pox ,
typhoid fever
Secondary to some other cancers
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