This document discusses platelets, including their history, formation, structure, functions, and role in hemostasis. Platelets are formed from megakaryocytes in the bone marrow and released into circulation. They are anuclear cell fragments that help form blood clots to stop bleeding. Platelets adhere to sites of vessel injury, become activated, and aggregate to form a platelet plug. They also release chemicals that promote coagulation and wound healing. Disorders can occur if platelets are dysfunctional or in inadequate numbers.

1. PLATELETS IN HEALTH AND DISEASE
Dr.AnuPriya J

2. SCHEME
• Introduction
• History
• Formation
• Structure
• Properties
• Functions
• Role in hemostasis
• Platelet function tests
• Antiplatelet drugs
• Platelet disorders
• Transfusion

3. Introduction
• Blood is a complex fluid consisting of plasma and of formed
elements – red blood cells, white blood cells & platelets.
• Platelets are small, anuclear, cytoplasmic fragments of
megakaryocytes
• Normal platelet count – 1.5 to 4 L / mm3 of blood

4. • Platelets survive in circulation for about 8-10 days
• Removal -by the mononuclear phagocyte system
-spleen plays a major role
• Half life – about 5 days
Introduction

5. History
• Hewson - in 1780 - very small undefined particles in blood.
• Max Schultze in 1865 - these particles must be degenerate
and disintegrated leukocytes – as they showed a granular
appearance.
• Riess in 1872 and Laptschinski in 1874 - leucocytes - mainly
during infectious diseases – are the origin of the Schultze's
corpuscles.

6. • George Hayem between the years 1878 and 1879 - related to
erythrocytes - considered as their precursors - the term
“haematoblasts”
• Neumann -1880 - stated they were artifacts derived from red
cells following an incorrect technique of venipuncture .
History

7. • Giulio Bizzozzero - the first - in 1882 - clearly establish the
significance of the particles- the third morphological element
of blood, totally unrelated to white and red cells - gave a more
precise description
• Bizzozzero named these elements “piastrine”, i.e. small plates
• Wright - Between 1906 and 1910 - identified bone marrow
megakaryocytes as precursors of blood platelets – first to use
the term “platelets”
History

8. • The invention of the aggregometer by Born in 1962 provided a
valuable instrument to study platelet function and
responsiveness to agonists
• In 1964, David-Ferreira published the first paper concerning
platelet ultrastructure analyzed by means of electron
microscopy.
History

9. • The late 20th century
- the definition and characterization of many platelet receptors
- the analysis of molecular mechanisms involved in signal
transduction
- the introduction of anti-platelet treatments
• Recent – collection, storage & transfusion
History

10. Formation
Pluripotent stem cells
Committed stem cells
CFU-Mega
Megakaryoblast
Basophil megakaryocyte
Granular megakaryocyte
Mature megakaryocyte
Platelets
Thrombopoiesis
CFU -
GEMM
CFU-
MegE
CFU-
Mega
TPO

12. Formation
• Thrombopoiesis – formation of platelets
• Regulated by
- Thrombopoietin
- Interleukin (IL-1,IL-3,IL-6,IL-11)
- GM-CSF
• Each megakaryocyte produces between 1,000 to 3,000 platelets
during its lifetime.
• An average of 1011 platelets are produced daily in a healthy adult.

13. •Small, granulated,
anuclear, discoid
•Diameter - 2 to 3 μm
•Volume - 8 fl
•Size - One fourth of
red cells
Structure

14. Granular contents
VWF

15. Properties

16. Functions
• Temporary hemostasis
• Blood coagulation
• Clot retraction
• Phagocytosis
• Storage & transport
• Wound healing & Vascular growth

17. Role in hemostasis

18. Role in hemostasis

19.  Adhesion
• VWF – GpIb/IX/V
• Collagen – GpIa/IIa
• Fibronectin & Laminin – GpIc/IIa
• Collagen – GpVI
Role in hemostasis

20. Role in hemostasis

21.  Activation & Release
Platelet agonists bind with specific membrane receptors
↓
G protein activation
↓
Activation of Phospholipase C
↓
Membrane inositol phospholipids
↓
IP3 , DAG
Role in hemostasis

22.  IP3
• A calcium ionophore
• Causes calcium to enter the cytosol from the dense tubular
system ( an internal platelet reservoir) and from the platelet
exterior
• A rising cytosolic calcium concentration
Role in hemostasis

23.  Calcium
Rising cytosolic calcium concentration
↓
Activation of myosin light chain kinase
↓
Phosphorylation of myosin light chain
↓
Reorientation of cytoskeletal proteins
↓
Platelet shape change,secretion and contraction
Role in hemostasis

24.  Calcium
• Contraction of the actin microfilaments – movement of
granules to the open canalicular system – release
• Calcium and platelet agonists also activates phospholipase A2
Role in hemostasis

25.  Activation & Release
G protein activation and calcium
↓
Activation of Phospholipase A2
↓
Membrane phosphatidylcholine
↓
Arachidonic acid
↓COX
PGH2
↓ Thromboxane synthase
TXA2
Role in hemostasis

26. • PGH2 – a cofactor enhancing the ability of collagen to function
as a platelet agonist
• TXA2 – binds to a specific platelet membrane receptor –
resultant activation of Phospholipase C – amplification of
platelet activation through further generation of IP3,DAG
Role in hemostasis

27. • Activated platelets change shape from disc to tiny sphere with
numerous projecting pseudopods
• Activated platelets exocytose the contents of their dense
storage granules and alpha granules
• Platelet activating factor (PAF) – cytokine – neutrophils,
monocytes & platelets ; produced from membrane lipids; acts
via G proteins
Role in hemostasis

28. • Locally damaged red cells also release ADP which further
activates the platelets
• Thrombospondin and Thrombonectin – facilitate contractile
system activity – promote exocytosis of granular contents.
• Thrombospondin – binds to fibrinogen n GP IV receptor
secondary phase of aggregation – larger, firmer aggregates
Role in hemostasis

29. Role in hemostasis

30. Role in hemostasis

31. Role in hemostasis

32. • Platelet activation – increased platelet coagulant activity
• Synthesize coagulation factor V
• Platelet phospholipids - Platelet factor 3 and 4 - accelerate the
formation of Va, VIIIa
• Va – conversion of prothrombin to thrombin
• Platelets play a major role in formation of intrinsic
prothrombin activator – clot formation
Role in hemostasis

33. XII XIIa
XI XIa
IXaIX
X Xa
VIIIaVIII
VII VIIa
X
Prothrombin
Intrinsic Pathway Extrinsic Pathway
VaV
Thrombin
Fibrinogen Fibrin monomer
Blood Coagulation Cascade
Collagen, HMW Kininogen, Kallikrein
↓
HMW Kininogen
Platelet phospholipids
Calcium
Platelet phospholipids
Calcium
Calcium
XIIIaXIII
Stable fibrin polymer(clot)
Release of tissue factor
(Tissue thromboplastin)
Platelet phospholipids
Calcium

34. Role in hemostasis

35.  The activated platelets incorporated in the clot rearrange and
contract their intracellular actin/myosin cytoskeleton.
 The intracellular actin network - internal part of GpIIb/IIIa
fibrinogen receptor.
 The external part of GpIIb/IIIa - the fibrin network of the clot
 As a result of platelet contractile force on the fibrin network,
the formed clot will compact on itself and hence reduce its
total volume.
Role in hemostasis
Clot retraction

36.  Platelet factor 4
 Platelet derived growth factor(PDGF)
 Transforming growth factor β
• Chemoattractants for WBCs, Smooth muscle cells &
fibroblasts.
• Activate these cells and accelerate wound healing.
• PDGF – Potent mitogen for vascular smooth muscle.
Role in hemostasis
Wound healing

37. Platelet function tests
• Platelet count
• Bleeding time
• Platelet aggregation test
• Platelet adhesiveness test
• Clot retraction time

38. Antiplatelet drugs

39. Bernard-Soulier Syndrome
(Giant Platelet Syndrome)
• Discovered by Jean Bernard and Jean-Pierre Soulier, 1948
• Abnormality of the platelet glycoprotein Ib-IX-V complex,
receptor for vWF – platelets cannot adhere
• Inherited in autosomal recessive manner
• Large platelets on peripheral blood smear
• Normal count, Prolonged bleeding time
• Decreased or absent glass bead retention
• Platelets aggregate wt physiological agonists but fail to
aggregate wt ristocetin (similar to Von Willebrand disease)

40. Glanzmann's thrombasthenia
• Platelets lack GPIIb/IIIa; hence, no fibrinogen binding can
occur
• Inherited in autosomal recessive manner
• Normal morphology and count
• Platelets less able to aggregate ; defective clot retraction
• Bleeding time is significantly prolonged
• Platelets do not aggregate with all aggregating agents but
they aggregate with ristocetin.

41. Granule defects
• δ storage pool disease – dense body deficiency
• α granule deficiency – grey platelet syndrome
• αδ storage pool disease
• δ storage pool disease
- Autosomal dominant
- Absence of dense bodies
- Seen in association with certain inherited disorders

42. Gray platelet syndrome
• A rare condition caused by a reduction or absence of the
platelet alpha granules, or of the proteins contained in these
granules
 Pseudo gray platelet syndrome
• Platelets in blood collected into EDTA appear gray and
agranular compared with platelets from citrated blood.
• EDTA-exposed platelets show extensive activation, with loss of
storage granule contents and pseudopod formation

43. Von Willebrand disease (vWD)
• Most common hereditary coagulation abnormality
• Arises from a qualitative or quantitative deficiency of vWF
• Hereditary – type 1, type 2, type 3.
• Acquired
• Normal count, Prolonged bleeding time
• Deficiency of factor VIII activity in the plasma
• Platelets aggregate wt physiological agonists but fail to
aggregate wt ristocetin
• Desmopressin – type 1 and 2 - stimulates release of VWF from
Weibel-Palade bodies of endothelial cells
• vWF replacement therapy – type 3 disease

44. Thrombocytopenia
• Pseudothrombocytopenia
• Decrease Production
– Marrow Damage
• Aplasia
• Drugs
• Malignancy
• Radiation
– Congenital Defects
– Ineffective Production
• B12, Folic Acid Def

45. • Increase Destruction
Non Immune
• Disseminated Intravascular Coagulation
• Thrombotic Thrombocytopenic Purpura
• HELLP syndrome
Immune
• Idiopathic Thrombocytopenic Purpura
• Heparin Induced Thrombocytopenia
• SLE, AIDS
• Thrombotic Thrombocytopenic Purpura
• Neonatal
• Post transfusion
Thrombocytopenia

46. Idiopathic Thrombocytopenic Purpura
• Autoimmune
• IgG autoantibody mediated platelet destruction
• Thrombocytopenia with normal or increased number of
megakaryocytes
• Diagnosis of exclusion
• Childhood/Adult onset
• Children – Acute; H/O viral infection , self-limiting
• Adults – F > M; Chronic; longer course
• 80% respond to Oral prednisolone – 3 months – if no
response – Splenectomy
• Intravenous immunoglobulin or Immunosuppressive drugs

47. Dengue hemorrhagic fever
• Characterized by severe thrombocytopenia with bleeding
manifestations
• Severity depends on the dengue virus subtype
• Concomitant infection with more than one subtype
• Dengue virus 2 – most severe – direct binding,
ultramicroscopic changes
• Cytotoxic factor ; increased proinflammatory cytokines
• Plasma leakage – decreased plasma proteins – decreased
fibrinogen
• PLATELET TRANSFUSION
• FRESH FROZEN PLASMA

48. Transfusion
• Platelets collected by apheresis – intermittent/continuous
flow cell separator.
• Single donor / Random donor platelet concentrate
• Storage - 20-24ᵒ C under constant agitation – 5 days
• Neither group specific or Rh specific – cross matching not
needed
• Indications – thrombocytopenia
• Contraindications – Immune mediated thrombocytopenia

49. Post transfusion
• 5-7 days after transfusion
• Allo antibodies
• Anti-P1A1 [Antigen located on gp IIIa subunit]
• Anti-Baka (Leka) [Antigen located on gp IIb subunit]
• Self – limiting ; 3-6 weeks
• High dose intravenous immunoglobulin – treatment of choice

50. References
• Boron & Boulpaep - Medical Physiology, 2nd Edition
• Ganong's Review Of Medical Physiology, 24th Edition
• Best & Taylor's Physiological Basis Of Medical Practice, 13/ E.
• Dacie And Lewis Practical Haematology 11th Edition
• de Gruchy's Clinical Haematology In Medical Practice, 5th Ed
• Arthropod borne viral diseases – Current status and research
– D.Raghunath Rao, C.Durga Rao
• Textbook of Medical Physiology G K Pal 2 E
• Internet references

54. • Alfred Donne -1842 «globulin du chyle» (that is to say small
globules derived from plasma) a sort of small globular, pale,
opaline corpuscles visible in blood.
• Later described by Beale in 1850 as particles of «germinal
matter» and by Zimmermann in 1860 as «small corpuscles»

55. Role in hemostasis

56. Clot retraction
 After the clot has been formed, the activated platelets
incorporated in the clot rearrange and contract their
intracellular actin/myosin cytoskeleton.
 The intracellular actin network is connected to the internal
part of the integrin αIIbβ3 fibrinogen receptor. Following
coagulation, the external part of αIIbβ3 will have bound to the
fibrin network of the clot, and therefore, as a result of platelet
contractile force on the fibrin network, the formed clot will
compact on itself and hence reduce its total volume.
 The mechanism is termed clot retraction.
Role in hemostasis