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.
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9. MICROTUBULES.
Made up of
Polymerised proteins
called Tubulins.
Forms compact
bundle below
membrane & encircle
whole cytoplasm.
Responsible for
discoid shape.
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13. CONTRACTILE PROTEINS.
Actin & Myosin – same as those of contractile
proteins of muscle.
Responsible for platelet contraction & clot retraction.
Thrombosthenin
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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
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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
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16. ENZYMES
Adenosine triphosphatase & enzyme for synthesis
of prostaglandins.
Prostaglandins – acts as a local hormone & have
local vascular & tissue reaction.
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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.
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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.
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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.
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21. ROLE IN CLOT FORMATION.
Play imp role in formation of intrinsic prothrombin
activator
It is responsible for onset of blood clotting.
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22. ROLE IN CLOT RETRACTION.
Contraction of
contractile proteins i. e
Actin, Myosin &
Thrombosthenin.
Responsible for clot
Retraction & wound
healing.
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23. ROLE IN REPAIR OF INJURED
BLOOD VESSELS.
Platelet derived growth
factor (PDGF) in
cytoplasm of platelet
imp for Repair of
Endothelium.
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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.
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25. TRANSPORT & STORAGE
FUNCTION.
Platelet when passes
through GIT takes 5-
HT against
concentration gradient,
stored & transported to
the site of injury.
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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.
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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.
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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
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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
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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.
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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
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34. CONTROL OF TROMBOPOIESIS.
Thrombopoietin –
Megakaryocyte –
colony stimulating
activity (Meg-CSA)
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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