Platelets are small, colorless cell fragments that help the body form clots to stop bleeding. They have a cell membrane and cytoplasm containing granules with proteins and enzymes. Platelets have receptors on their surface that allow them to adhere to sites of injury in blood vessels. Their normal lifespan is 8-12 days, after which they are destroyed by the spleen. Platelets play key roles in hemostasis, forming clots to plug leaks in blood vessels and promoting clot formation and retraction.

3.  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

4.  Structure:
 Cell membrane
 Microtubule
 Cytoplasm

5.  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

6.  Platelets has prominent cytoskeleton
 Microtubule
 microfilament

7.  Golgi apparatus
 Endoplasmic reticulum
 Mitochondria
 Microtubule
 Micro vesicles
 Microfilaments
 Granules
 Proteins
 Enzymes
 Hormones.
 Chemical substances

8. The major proteins present are contractile
proteins which are responsible for the
contraction of platelets:
 Actin
 Myosin
 Thrombosthenin

9.  Fibrin-stabilizing factor…. Clotting factor
 Platelet derived growth factor (PDGF)
............. helps repair damaged vascular
walls.
 Von willibrand factor

10.  Alpha granules
 Dense granules

12.  The enzymes present are adenosine
triphosphatase and the enzymes
necessary for the synthesis of
prostaglandin

14.  Destroyed in spleen
 Life span 8-12 days

15.  Adhesiveness
 Aggregation
 Agglutination

17.  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

18.  Normal count – 1.5 – 4.5 lac/cubic mm
 Physiological variation age , sex, food,
exercise , altitude
 Variation with disease
 Thrombocytosis
 Thrombocytopenia

19.  After splenctomy
 After severe injury , hemorrhage , major
surgery
 Blood cancers like CML , myelofibrosis

20.  Idiopathic thrombocytopenic purpura
 Bone marrow depression due to drugs ,
radiation
 Hypersplenism
 Infections like dengue , chicken pox ,
typhoid fever
 Secondary to some other cancers