physiology of platelets

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