PLATELETS

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

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

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

STRUCTURE & COMPOSITION
 Leishmann’s staining
– faint blue cytoplasm
with reddish purple
granules.
 Nucleus - Absent.

ELECTRON MICROSCOPIC
PICTURE.
 Cell membrane.
 Microtubules.
 Cytoplasm.

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

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.

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.

MICROTUBULES.
 Made up of
Polymerised proteins
called Tubulins.
 Forms compact
bundle below
membrane & encircle
whole cytoplasm.
 Responsible for
discoid shape.

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

GOLGI APPARATUS,
ENDOPLASMIC RETICULUM
 Synthesizes various
Enzymes.
 Endoplasmic
Reticulum – stores
large amount of
calcium.

MITOCHONDRIA
 Power house of cell.
 Produce ATP & ADP.

CONTRACTILE PROTEINS.
 Actin & Myosin – same as those of contractile
proteins of muscle.
 Responsible for platelet contraction & clot retraction.
 Thrombosthenin

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

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

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

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

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.

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.

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.

ROLE IN CLOT FORMATION.
 Play imp role in formation of intrinsic prothrombin
activator
 It is responsible for onset of blood clotting.

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

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

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

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

NORMAL COUNT &
VARIATIONS.
 Normal count.
 150,000 – 400,000
per mm3
 Avg 2.5 L/mm3

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.

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.

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

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

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

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.

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

CONTROL OF TROMBOPOIESIS.
 Thrombopoietin –
 Megakaryocyte –
colony stimulating
activity (Meg-CSA)

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.

PLATELETS

More Related Content

What's hot

Viewers also liked

Similar to PLATELETS

More from Dr Nilesh Kate

Recently uploaded

PLATELETS