PLATELETS

PLATELETS

1. DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
DEPT. OF PHYSIOLOGY
PLATELETS

2. OBJECTIVES
Structure &
composition.
Properties & functions
Normal count &
variations.
Formation of platelets.
Life span & fate of
platelets.
Thursday, June 16, 2016

3. STRUCTURE & COMPOSITION.
Platelets – small plate like.
Thrombocytes. – thrombo –
clot; cytes—cells.
Size – smallest blood cells ;
2-4 μm.
Shape – spherical or oval
discoid
Volume 5.8 μm3.
Colour – colourless
Thursday, June 16, 2016

4. STRUCTURE & COMPOSITION
Leishmann’s staining
– faint blue cytoplasm
with reddish purple
granules.
Nucleus - Absent.
Thursday, June 16, 2016

5. ELECTRON MICROSCOPIC
PICTURE.
Cell membrane.
Microtubules.
Cytoplasm.
Thursday, June 16, 2016

6. CELL MEMBRANE.
6 nm thick trilaminar
membrane.
Consists of
Lipids – phospholipids,
cholesterol &
glycolipids.
Carbohydrates.
Proteins –
glycoproteins.
Thursday, June 16, 2016

7. CELL MEMBRANE.
Phospholipids of membrane
contains platelet factor -3 ,
imp for blood clotting
process.
Glycoproteins – forming
surface coat of platelets
Prevent sticking of platelets to
endothelium.
Accelerate adherence to
collagen & damaged
endothelium.
Thursday, June 16, 2016

8. CELL MEMBRANE.
Canalicular system –
surface of platelets
invaginate to form
Canalicular system or
surface connecting system.
Receptors -- For combining
with collagen & fibrinogen.
Precursors of substances
like – Thromboxane A2, PG,
LT & platelet factor 3,4 are
also present.
Thursday, June 16, 2016

9. MICROTUBULES.
Made up of
Polymerised proteins
called Tubulins.
Forms compact
bundle below
membrane & encircle
whole cytoplasm.
Responsible for
discoid shape.
Thursday, June 16, 2016

10. CYTOPLASM.
Contains – Golgi
apparatus, Endoplasmic
reticulum, Mitochondria,
microtubules,
microvesicles, filament,
granules, glycogen,
Lysosomes, protein
enzymes & hormonal
substances.
Thursday, June 16, 2016

11. GOLGI APPARATUS,
ENDOPLASMIC RETICULUM
Synthesizes various
Enzymes.
Endoplasmic
Reticulum – stores
large amount of
calcium.
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12. MITOCHONDRIA
Power house of cell.
Produce ATP & ADP.
Thursday, June 16, 2016

13. CONTRACTILE PROTEINS.
Actin & Myosin – same as those of contractile
proteins of muscle.
Responsible for platelet contraction & clot retraction.
Thrombosthenin
Thursday, June 16, 2016

14. OTHER PROTEINS
Fibrin stabilizing Factor – Imp in blood coagulation.
Platelet derived growth factor – for growth of vascular
endothelial cells, vascular smooth cells & fibroblast
Involved in repair of damaged blood vessel.
Von-Willebrand factor – for platelet adherence
Thursday, June 16, 2016

15. GRANULES
Dense granules –
contains phospholipids,
triglycerides, cholesterol,
ATP,ADP, Serotonin (5HT-
which hey obtain while
passing through GIT)
Alpha granules –
contains secreted proteins
as clotting factors, & PDGF
Thursday, June 16, 2016

16. ENZYMES
Adenosine triphosphatase & enzyme for synthesis
of prostaglandins.
Prostaglandins – acts as a local hormone & have
local vascular & tissue reaction.
Thursday, June 16, 2016

17. PROPERTIES
Adhesiveness –
whenever comes in
contact with any wet or
rough surface gets
activated & stick to
surface.
Factors responsible are –
collagen, thrombin, ADP,
thromboxane A2, Ca ion
& Von-Willebrand Factor
Thursday, June 16, 2016

18. PROPERTIES
Aggregation – property
to stick to each other
Factors responsible are
ADP & Thromboxane A2
Agglutination –
property of clumping
together of platelet
Its due to platelet
Agglutinins.
Thursday, June 16, 2016

19. FUNCTIONS
Role in haemostasis.
Role in clot formation.
Role in clot retraction.
Role in repair of injured blood vessels.
Role in Defense mechanism.
Transport & storage function.
Thursday, June 16, 2016

20. ROLE IN HAEMOSTASIS.
Haemostasis – spontaneous arrest of bleeding from injured
blood vessel.
Vasoconstriction – by 5HT & other vasoconstrictors
Temporary haemostatic plug – by platelets due to its
property of adhesiveness & aggregation.
Definite haemostatic plug – also initiated by platelets.
Thursday, June 16, 2016

21. ROLE IN CLOT FORMATION.
Play imp role in formation of intrinsic prothrombin
activator
It is responsible for onset of blood clotting.
Thursday, June 16, 2016

22. ROLE IN CLOT RETRACTION.
Contraction of
contractile proteins i. e
Actin, Myosin &
Thrombosthenin.
Responsible for clot
Retraction & wound
healing.
Thursday, June 16, 2016

23. ROLE IN REPAIR OF INJURED
BLOOD VESSELS.
Platelet derived growth
factor (PDGF) in
cytoplasm of platelet
imp for Repair of
Endothelium.
Thursday, June 16, 2016

24. ROLE IN DEFENCE MECHANISM.
Due to the property of
agglutination , platelets
are capable of
Phagocytosis.
Mainly in Phagocytosis
of carbon particles,
viruses & immune
complexes.
Thursday, June 16, 2016

25. TRANSPORT & STORAGE
FUNCTION.
Platelet when passes
through GIT takes 5-
HT against
concentration gradient,
stored & transported to
the site of injury.
Thursday, June 16, 2016

26. NORMAL COUNT &
VARIATIONS.
Normal count.
150,000 – 400,000
per mm3
Avg 2.5 L/mm3
Thursday, June 16, 2016

27. PHYSIOLOGICAL VARIATIONS.
Age – Less in infant, reach adult level by 3 months of age.
Sex – No difference but during mensturation reduced in
females.
Meal – Increases after meal
Muscular exercise – Increases.
High Altitude – Increases.
Thursday, June 16, 2016

28. PATHOLOGICAL VARIATIONS.
Thrombocytosis.
Increase in count more than 450,000/mm3
 After Splenectomy
After hemorrhage, severe injury, major operation &
parturition.
Myloproliferative Disorders – CML, Polycythemia vera,
Myelofibrosis.
Thursday, June 16, 2016

29. PATHOLOGICAL VARIATIONS.
Thrombocytopenia
Decrease in count less than
150,000/mm3
ITP
Bone marrow depression
Acute leukemia
Infections
Toxaemia, septicemia &
uremia.
Thursday, June 16, 2016

30. FORMATION OF PLATELETS.
Stages in platelets
production.(10 days)
Megakaryoblast.
Promegakaryocyte.
Megakaryocyte.
Sites – Bone Marrow
Stem cells – PHSC
CFU- Meg
Thursday, June 16, 2016

31. MEGAKARYOBLAST.
Earliest recognizable
cells.
CFU-Meg differentiate to
form Megakaryoblast.
Diameter – 20-30 mm
Cytoplasm – small, blue,
Non-granular
Nucleus – large,
oval/kidney shaped
Thursday, June 16, 2016

32. PROMEGAKARYOCYTE
Megakaryoblast –
Endoreduplication of
nuclear chromatin.
Nuclear chromatin
replicates in multiple of 2
without division of cell.
Large cell with 32 times
diploid content of nuclear
DNA formed.
Cytoplasm – Granular.
Thursday, June 16, 2016

33. MEGAKARYOCYTE.
Diameter – large cell with
30-90mm in diameter.
Nucleus- single multiloaded.
Cytoplasm – abundant with
red purple granules.
Cell margin – irregular with
many Pseudopodia which
gets detached into blood &
forms platelets.
One Megakaryocyte – 4000
platelets
Thursday, June 16, 2016

34. CONTROL OF TROMBOPOIESIS.
Thrombopoietin –
Megakaryocyte –
colony stimulating
activity (Meg-CSA)
Thursday, June 16, 2016

35. LIFE SPAN & FATE OF
PLATELETS.
Life span – 8-12 days
Avg – 10 days.
Fate – Destroyed by tissue macrophage system in
spleen.
Splenomegaly – reduces platelet count.
Splenectomy – increases platelet count.
Thursday, June 16, 2016

36. Thank
You