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Oral epithelium

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In Depth Description of the oral epithelium

Publicada em: Saúde e medicina
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Oral epithelium

  1. 1. 1
  2. 2. PRESENTED BY DR SHRIKANT SONUNE GUIDED BY DR ASHOK PATIL DR SHILPA KANDALGAONKAR DR MAYUR CHOUDHARI DR SUYOG TUPSAKHARE DR MAHESH GABHANE
  3. 3. INTRODUCTION Epithelium Membrane Cutaneous membrane Mucous membranes (mucosa) Serous membranes (serosa) Endothelium Glands
  4. 4. Oral mucosa  Epithelium- Stratified Squamous Epithelium  Connective tissue a lamina propria submucosa.  Oral mucosa is divided a/c to function into 1. Lining mucosa, 2. Masticatory mucosa, 3. Specialized mucosa
  5. 5. Specialized mucosa Lining mucosa Masticatory mucosa Oral mucosa
  6. 6. Lining Mucosa  Forms about 60% of surface area  Nonkeratinized  Distensible  Relatively loosely bound .  Found over mobile structures like the lips, cheeks, soft palate, alveolar mucosa, vestibular fornix, and the floor of the mouth.
  7. 7. Masticatory Mucosa  Form 25% of surface area  Keratinized  Rigid,  Tough  Tightly bound .  Protective-covering component of Gingiva Hard palate Alveolar ridge
  8. 8. Specialized Mucosa  It is located on the dorsum of the tongue.  Specialized mucosal structures the lingual papillae and taste receptors.  The heterogeneous pattern of keratin expression in the tongue is complex  In part is responsible for generating the papillary architecture of the lingual epithelium.
  9. 9. Keratinized epithelium Nonkeratinized epithelium  Superficial layer show no nuclei(or pyknotic)  Comparatively thin  Increase in size comparatively less  Filaments aggregates in bundle  Superficial layer show viable nuclei  Comparatively thick  Increase in size comparatively more  Filaments are dispersed
  10. 10. Keratinized epithelium Nonkeratinized epithelium  Odland bodies are elongated & contain a series of parallel lamellae  Effective barrier  Keratohyalin granules associated with tonofilaments  Odland bodies are circular with amorphous core  Forms comparatively less effective barrier  Keratohyalin granules are not associated with tonofilaments
  11. 11. Over view of oral epithelium Architectural integrity Function Cell to cell attachment Mechanical, Basal lamina Chemical, Keratin cytoskeleton Microbial barrier, Signaling functions. Major cell type Other cell type Keratinocytes Langerhans cells, Merkel cells, Melanocytes, Constant renewal Replacement of damage cells
  12. 12. Structure of Basement membrane  A specialized extracellular molecular network, constructed jointly by epithelial and connective tissue cells.  Pink-to-purple band approximately 0.5µm thick  The basement membrane consists of - Lamina densa - Lamina lucida - Lamina reticularis
  13. 13. Structure of Basement membrane
  14. 14. Basal lamina  Basal lamina : Joins the epithelium to the underlying connective tissue  It consist of lamina densa & lamina lucida.  The lamina densa a fibrillar layer  The lamina rarae or lamina lucida electron-lucent layer. (Recent studies have shown that the lamina lucida is a preparation artifact produced during tissue dehydration. In reality, the basal lamina consists solely of a lamina densa in direct juxtaposition to the cell membrane.)
  15. 15.  Approximately 400 Å beneath the epithelial basal layer  Produced by the basal cells  Light microscope Structure less zone  PAS stain positive
  16. 16. Basal lamina  Lamina lucida : Laminin  Lamina densa : Type IV collagen +heparan sulphate (chicken wire configuration )  Permeable to fluids but acts as a barrier to particulate matter
  17. 17. Lamina Reticularis  Characterized by a reticular network of collagens (other than type IV).  Merges with the underlying connective tissue.  Anchoring fibrils (type VII collagen),  Along with type I, type II
  18. 18. Function of Basement membrane Foundation for epithelium Line of demarcation Promotes differentiation of epithelium Promote peripheral nerve regeneration & growth  Also tend to prevent metastases
  19. 19. Cytoskeleton of epithelium Diameter Molecular wt Smaller Microfilaments 4-6nm 25kda Intermediate filaments 7-11nm 40-200kda Large microtubules 25nm 55kda
  20. 20. Intermediate Filaments  Essential components of the cytoskeleton and nucleoskeleton of all cells.  Intermediate Filaments are products of the largest family of cytoskeleton protein genes.  In humans, at least 65 members of this multigene family are presently known to encode these 10-12 nm filaments.  Epithelia have been characterized by containing Specific types of proteins , that proteins known as cytokeratins, which form the largest group of Intermediate Filaments with about 50 genes.
  21. 21. Cytokeratins  5classes of intermediate filaments have been described: i Acidic cytokeratins; Cytoplasmic ii Basic cytokeratins; Intermediate Filaments iii Vimentin, desmin iv Neurofilaments Nuclear v Nuclear lamins Intermediate Filaments
  22. 22. Cytokeratins Acidic (type 1 cytokeratins ) Basic (Neutral, type II cytokeratins) CK10, CK12,CK13, CK14, CK16, CK17, CK18,CK19 and CK20 CK1, CK2, CK3, CK4, CK5, CK6, CK7, CK8 and CK9
  23. 23. Cytokeratins  Keratin proteins : Numbered in a sequence contrary to their molecular weight E.g. Lower molecular weight keratins (such as K19, )  Always occurs in pairs of combination of type 1 & type11  Absence of pair susceptible to degeneration by proteases  Cytokeratins shows tissue & layer specificity
  24. 24. Function of Cytokeratins Form a complex network which extends from the surface of the nucleus to the cell membrane. Organization of the cytoplasm and cellular communication mechanisms. Supporting the nucleus and providing tensile strength to the cell. Interact with desmosomes and hemidesmosomes.
  25. 25. Stratified Squamous epithelium  Stratified Squamous keratinizing epithelium (cutaneous type)  Stratified Squamous Parakeratinizing epithelium  Stratified Squamous Nonkeratinizing epithelium(mucous type)
  26. 26.  Oral epithelium :stratified Squamous epithelium  4 classical epithelial strata 1. Stratum basale 2. Stratum spinosum 3. Stratum granulosum 4. Stratum corneum
  27. 27.  The principal cell type : Keratinocyte  Other cells : Non-keratinocytes / Clear cells Langerhans cells Merkel cells Melanocytes Inflammatory cells
  28. 28. Stratum basale  Cells in the basal layer : single layer of Cuboidal to columnar .  Their nuclei are round to ovoid  Situated away from basement membrane.  All cell organelles are present.  Filaments comprising k5 and k14 keratin chains occupy roughly 25% of the cytoplasmic volume.
  29. 29. Basal cells synthesize and secrete 1.Type IV and type VII collagens, 2.Laminin, 3.Perlecan, 4.Parathyroid hormone- related peptide, 5.Cytokines(k5& k14) As the cells differentiate, the nucleus-to-cytoplasmic ratio decreases.
  30. 30. Cell renewal Cell loss Approximately 1 month Keratinocyte reach the outer epithelial surface, where it becomes shed from the stratum corneum Epithelium maintains a constant thickness.
  31. 31. Cell renewal  Turn over time is follows- 1) For skin-52 to 75 days 2)For gut-4 to 14 days 3)For gingiva -41 to 57 days 4)Buccal mucosa -25 days It depend on regional differences.  Certain agents like cancer chemotherapeutic drugs & inflammation affects epithelial turnover time.
  32. 32. Stratum Basale Stem cells Serrated cells
  33. 33. Stem cells  Nonserrated basal cells contain only a few cytoplasmic organelles and appear to be the least differentiated cells in the epidermis.  High nucleus-to-cytoplasmic ratio,  Expression of k19,  Relative lack of keratin filament bundles,
  34. 34. Stem cells  High levels of integrins.  Contain melanin pigment as a result of their close association with melanocytes.  Expression of bcl-2 protein, an inhibitor of apoptosis.  Administration of bromodeoxyuridine.
  35. 35. Proliferation
  36. 36. Serrated type cell  Also known as transit amplifying cells.  They have a serrated basal surface in contact with the basement membrane.  Numerous cytoplasmic processes (pedicles) that project into the underlying connective tissue create the serrated appearance.  These basal cells appear specialized for anchoring the epidermis to the connective tissue.  The pedicles are rich in hemidesmosomes and have well-developed filament bundles terminating at the attachment plaques.
  37. 37.  Stratum spinosum  Large, polyhedral cells  Short cytoplasmic processes resembling spines  Prickly appearance(spiny appearance ?)  Cohesion : Desmosomes Located between the cytoplasmic processes of adjacent cells
  38. 38. Stratum spinosum  The stratum Spinosum forms the first layer of the differentiation compartment.  Most active in protein synthesis  Here the expression of k1 and k10 keratins increases, while that of k5 and k14 decreases.  Cell-to-cell attachment increases dramatically  Membrane-coating granules or lamellar granules are assembled in the Golgi complex
  39. 39. Stratum spinosum  They contain lamellar plates of fatty acids, cholesterol, and sphingolipids.  These lipid plates are released by exocytosis into the intercellular spaces at the upper layers of the stratum granulosum.  This all changes indicate their biochemical commitment to keratinization.
  40. 40.  Stratum Granulosum And Stratum Corneum  Stratum granulosum Keratohyalin granules  Stratum granulosum  Stratum corneum  Very sudden keratinization of the cytoplasm of the keratinocyte & conversion into horny squame Abrupt transition
  41. 41. Stratum Granulosum  Flatter & wider cells larger than spinous layer.  Derives its name from its content of Keratohyalin granules.  The nuclei show signs of cell degeneration & pyknosis.  m-RNA for filaggrin, the principal component of the Keratohyalin granules and for loricrin and involucrin, precursors of the cell envelope, increase in amounts in the stratum granulosum.
  42. 42. Stratum Granulosum  Membrane-coating granules continue to increase in number and migrate to the peripheral cytoplasm close to the plasma membrane in the outer layers of stratum granulosum.  Also known as keratinosomes, odland body , lamellar granules  Discharge content into intercellular space forming an intercellular lamellar material.
  43. 43. Filled with keratin Apparatus for protein synthesis & energy production lost  Complete keratinization Orthokeratinized  Parakeratinized epithelium  Nonkeratinized epithelium Intermediate stages of keratinization Stratum corneum
  44. 44.  Orthokeratinized epithelium No nuclei in the stratum corneum Well-defined stratum granulosum Stratum corneum
  45. 45.  Parakeratinized epithelium Stratum corneum retains pyknotic nuclei Keratohyalin granules : Dispersed Stratum corneum
  46. 46.  Nonkeratinized epithelium Has neither granulosum nor corneum strata Superficial cells : Viable nuclei (shows stratum Basale, intermedium, superficiale)
  47. 47.  Proliferation and differentiation of the keratinocyte Proliferation : Mitosis in the basal layer and less frequently in the suprabasal layers Differentiation : Keratinization
  48. 48.  Events of continuous differentiation Cells lose the ability to multiply by mitotic division Produce elevated amounts of protein, and accumulate keratohyalin granules, keratin filaments and macromolecular matrix in their cytoplasm Lose the cytoplasmic organelles responsible for protein synthesis and energy production
  49. 49. Eventually degenerate into a cornified layer due to the process of intracellular keratinization, but without loss of cell-cell attachment Finally sloughed away from the epithelia surface and into the oral cavity as the cell-cell attachment mechanisms (that is, hemidesmosomes and gap junctions) ultimately disintegrate
  50. 50.  Morphologic changes Progressive flattening  Prevalence of tonofilaments  Intercellular junction Keratohyaline granules Disappearance of the nucleus Str. basale Str. spinosum Str. granulosum
  51. 51.  Stratum corneum : K1 ,  Other proteins  Keratolinin  Involucrin  Filaggrin Keratohyalin granules Filaggrin Matrix of corneocyte
  52. 52.  Corneocytes Bundles of keratin tonofilaments Amorphous matrix of filaggrin Resistant envelope under the cell membrane  Interconnections Desmosomes Tight junctions (zonae occludens) : Less frequently
  53. 53.  Deeper strata Numerous mitochondria Succinic dehydrogenase Nicotinamide-adenine dinucleotide  Cytochrome oxidase Other mitochondrial enzymes Active tricarboxylic cycle Aerobic glycolysis
  54. 54.  Uppermost cells of the stratum spinosum Keratinosomes or odland bodies Modified lysosomes Acid phosphatase : Enzyme involved in the destruction of organelle membranes
  55. 55. NONKERATINOCYTES  Do not possess cytokeratins filaments hence do not have the ability to keratinize.  Not arranged in layers  Dendritic and appear unstained or clear  They are identified by special stains or by immunocytochemical methods.  These cells migrate to the oral epithelium 1. From neural crest 2. From bone marrow.
  56. 56. Melanocytes Langerhans cells Inflammatory cell Merkel's cells Non- keratinocyte NONKERATINOCYTES
  57. 57.  Originate from neural crest cells  Dendritic cells  Premelanosomes or melanosomes  Melanophages or Melanophores Tyrosine Dopa Melanin Tyrosinase MELANOCYTES
  58. 58. MELANOCYTES  Residing in the basal layer  Establishes contact with about 30-40 keratinocytes through their dendritic processes.  Melanin produced by melanocytes Melanosome  Melanocytes detected by The dopa reaction Silver-staining techniques. Mosan Fontana stain  Keratinocytes release mediators essential for normal melanocytes function.
  59. 59.  Dendritic cells  Modified monocytes (hematopoietic origin)  Mononuclear phagocyte system  Macrophages with possible antigenic properties  Antigen-presenting cells for lymphocytes  G-specific granules (Birbeck's) LANGERHANS CELLS
  60. 60.  It stains with Gold chloride, ATPase, Immunofluorescent markers.  Penetrate the epithelium from lamina propria.  Has vimentin-type intermediate filaments.  In the presence of antigenic challenge by bacterial plaque Langenhans cells migrate into the gingiva.  They also migrate into the epithelium in response to chemotactic factors released by the keratinocytes to the surface receptors of Langerhans cells.  They shuttle between epithelium & regional lymph nodes
  61. 61.  Originate from neural crest  Present in Basal layer  Harbour nerve endings  Not dendritic  Occasional desmosomes  Tactile preceptors  Stained by PAS stain. MERKEL CELL
  62. 62.  Clinical normal areas of mucosa  Nucleated cell layers  Transient  Lymphocytes : Most frequent Associated with langerhans cells  Polymorphonuclear leukocytes  Mast cells Inflammatory cells
  63. 63. Lateral Surface Specializations 64
  64. 64. Cell junctions  These are the sites where some kind of special contact can be recognized between the cells Can be classified in 3main types 1. Tight junction 2. Adhering junction 3. Gap junction (communicating junction)
  65. 65. Cell junctions Another terms related to junctions are 1. Zonula a junction that extends around the perimeter of cell like a belt. 2. Fascia if the junction occupies only the strip or patch of cell surface. 3.Macula small & circular in outline.
  66. 66. types of Junctions in epithelia. 1. Zonula occludens 2. Zonula adherens 3. Macula communicans 1) Tight junction. Zonula occludens (occluding junction, tight junction) occurs on the lateral cell surfaces just beneath the apical poles. 67
  67. 67. Structure of Tight junction Formed by interactions of special trans membrane proteins (claudins, occludin) in the plasma membranes of adjacent cells, these junctions form a network that extends completely around the cell perimeter and represent the closest contacts between cells. 68
  68. 68. Functions. Restrict Paracellular Flow by restricting intercellular movement of materials. Restrict Membrane Flow They separate the apical and basolateral domains in cell membranes, which insures that specific proteins will remain in specific domains. 69
  69. 69. 2. Zonula adherens It is also a band-like junction that extends around the perimeter of cells; it serves in the attachment of adjacent epithelial cells. Most numerous in oral epithelium. 70
  70. 70. Macula communicans  also known as -communicating junction -macula communicans, -maculae communicantes  This is a junctional area of between adjacent cells that facilitates intercellular communication by allowing the passage of small molecules and ions across the narrow intercellular gap through a multitude of junctional pores. 71
  71. 71. Structure of Macula communicans The junction consists of a hexagonal lattice of connexin protein subunits called connexons, which form intramembrane hydrophilic channels connecting the cytoplasm of adjacent cells. 72
  72. 72. 73 Function.  Permit intercellular signaling and electrical coupling by allowing the regulated passage of ions and small molecules between cells.  Important cellular strategy for approaching the efficiency of a syncytium. {Pathologic hyperplasia & metaplasia usually accompanied by reduction in gap junction communication.}
  73. 73. Macula adherens (desmosome)  Desmosomes are adhesive intercellular junctions, which are found in tissues subjected to mechanical strain.  Widespread in epithelia,  Particularly in stratified Squamous varieties.  Intermediate (keratin) filament cytoskeletons across cells.  These junctions are “spot welds” between adjacent cells,  Which are formed by the juxtaposition and attachment of two symmetrical disk-shaped structures provided by each cell. 74
  74. 74. a. Structure: light microscopic. At the Light Microscopic level, only observed in Stratified Squamous Epithelium due to their high density between cells.  They appear as small punctate bodies,  Hence onces they were considered as “cytoplasmic bridges” 75
  75. 75. Structure: electron microscopic Their ultra structure revealed that desmosomes are bipartite junctions, which consist of symmetrical, mirror- image-like components provided by each adjacent cell. 76
  76. 76.  Intracellular components Inside each cell, just beneath their lateral plasma membranes, electron dense structures called attachment plaques were found to connect the cell membrane on one side with intermediate filaments of the keratin cytoskeleton on the cytoplasmic side.  Extracellular components Between each cell in the middle of the intercellular space, an intermediate dense midline was observed, which appeared to be a region of attachment between adjacent cells. 77
  77. 77. c. Structure: submicroscopic. At the molecular level,  specialized adhesive proteins. major components cadherin superfamily of adhesion molecules. two major desmosomal cadherins have been described and a schema for their nomenclature proposed desmocollins and desmogleins. Region-specific expression for various isoforms of these proteins has also been shown to occur in Stratified Squamous Epithelium. 78
  78. 78. Function.  Most abundant in lining membranes subject to wear and tear,  Present in all epithelia,  desmosomes are important cellular spot welds that hold cells together by a calcium dependent adhesion mechanism.  They represent an important means of resistance to lateral shearing forces between cells by coupling external attachment of adjacent cells to internal linkage of their keratin cytoskeletons across the epithelium. 79
  79. 79. Structure of mucosa in different regions  Soft palate – thin (150micron), nonkeratinized stratified Squamous epithelium ,taste buds present  Ventral surface of tongue- thin nonkeratinized stratified Squamous epithelium  Floor of mouth-very thin (100micron),nonkeratinized stratified Squamous epithelium
  80. 80. Structure of mucosa in different regions  Alveolar mucosa- thin nonkeratinized Squamous epithelium.  Labial & buccal mucosa -very thick (500micron),nonkeratinized stratified Squamous epithelium  Lips vermilion zone -thin Orthokeratinized Squamous epithelium  Lips intermediate zone- thin Parakeratinized stratified Squamous epithelium
  81. 81. Structure of mucosa in different regions  Gingiva -thick (250micron) Orthokeratinized /Parakeratinized stratified Squamous epithelium, showing stippled appearance.  Hard palate- thick Orthokeratinized , stratified Squamous epithelium thrown into transverse palatine ridges (rugae).  Dorsal surface of tongue- thick keratinized & non keratinized stratified epithelium Squamous epithelium forming 3 types of lingual papillae, some bearing taste buds.
  82. 82. References  Orel cells & tissue by P. R. Garant,  Orbans oral histology & embryology (11th edition ,12th edition)  Oral histology 5th edi ten cate  Histo notes by aw gustafson
  83. 83. 87

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