oral epithelium
TRANSCRIPT
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PRESENTED BY
DR SHRIKANT SONUNE
GUIDED BY
DR ASHOK PATIL
DR SHILPA KANDALGAONKAR
DR MAYUR CHOUDHARI
DR SUYOG TUPSAKHARE
DR MAHESH GABHANE
INTRODUCTION
Epithelium
Membrane
Cutaneous membrane
Mucous membranes
(mucosa)
Serous membranes
(serosa)Endothelium
Glands
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
Specialized mucosa
Lining mucosa
Masticatorymucosa
Oral mucosa
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.
Masticatory Mucosa Form 25% of surface area
Keratinized
Rigid,
Tough
Tightly bound .
Protective-covering component of
Gingiva
Hard palate
Alveolar ridge
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.
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
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
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
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
Structure of Basement membrane
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.)
Approximately 400 Å beneath the epithelial basal
layer
Produced by the basal cells
Light microscope
Structure less zone
PAS stain positive
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
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
Function of Basement membrane Foundation for epithelium
Line of demarcation
Promotes differentiation of epithelium
Promote peripheral nerve regeneration & growth
Also tend to prevent metastases
Cytoskeleton of epitheliumDiameter Molecular wt
Smaller Microfilaments
4-6nm 25kda
Intermediate filaments
7-11nm 40-200kda
Large microtubules
25nm 55kda
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.
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
CytokeratinsAcidic (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
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
Function of CytokeratinsForm 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.
Stratified Squamous epithelium
Stratified Squamous keratinizing epithelium (cutaneous type)
Stratified Squamous Parakeratinizing epithelium
Stratified Squamous Nonkeratinizing epithelium(mucous type)
Oral epithelium :stratified Squamous epithelium
4 classical epithelial strata
1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4. Stratum corneum
The principal cell type : Keratinocyte
Other cells : Non-keratinocytes / Clear cells
Langerhans cells
Merkel cells
Melanocytes
Inflammatory cells
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.
Basal cells synthesize and secrete1.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.
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.
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.
Stratum Basale
Stem cells Serrated cells
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,
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.
Proliferation
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.
Stratum spinosum
Large, polyhedral cells
Short cytoplasmic processes resembling spines
Prickly appearance(spiny appearance ?)
Cohesion : Desmosomes
Located between the
cytoplasmic processes
of adjacent cells
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
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.
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
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.
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.
Filled with keratin
Apparatus for protein synthesis & energy production
lost
Complete keratinization Orthokeratinized
Parakeratinized epithelium
Nonkeratinized epithelium
Intermediate
stages of
keratinization
Stratum corneum
Orthokeratinized epithelium
No nuclei in the stratum corneum
Well-defined stratum granulosum
Stratum corneum
Parakeratinized epithelium
Stratum corneum retains pyknotic nuclei
Keratohyalin granules : Dispersed
Stratum corneum
Nonkeratinized epithelium
Has neither granulosum nor corneum strata
Superficial cells : Viable nuclei
(shows stratum Basale, intermedium, superficiale)
Proliferation and differentiation of the keratinocyte
Proliferation : Mitosis in the basal layer and less
frequently in the suprabasal layers
Differentiation : Keratinization
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
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
Morphologic changes
Progressive flattening
Prevalence of tonofilaments
Intercellular junction
Keratohyaline granules
Disappearance of the nucleus
Str. basale
Str. spinosum
Str. granulosum
Stratum corneum : K1 ,
Other proteins
Keratolinin
Involucrin
Filaggrin
Keratohyalin granules Filaggrin Matrix of corneocyte
Corneocytes
Bundles of keratin tonofilaments
Amorphous matrix of filaggrin
Resistant envelope under the cell membrane
Interconnections
Desmosomes
Tight junctions (zonae occludens) : Less frequently
Deeper strata
Numerous mitochondria
Succinic dehydrogenase
Nicotinamide-adenine dinucleotide
Cytochrome oxidase
Other mitochondrial enzymes
Active tricarboxylic
cycle
Aerobic glycolysis
Uppermost cells of the stratum spinosum
Keratinosomes or odland bodies
Modified lysosomes
Acid phosphatase : Enzyme involved in the
destruction of organelle membranes
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.
MelanocytesLangerhans
cells
Inflammatory cell
Merkel's cells
Non-keratinocyte
NONKERATINOCYTES
Originate from neural crest cells
Dendritic cells
Premelanosomes or melanosomes
Melanophages or Melanophores
Tyrosine
Dopa
Melanin
Tyrosinase
MELANOCYTES
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.
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
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
Originate from neural crest
Present in Basal layer
Harbour nerve endings
Not dendritic
Occasional desmosomes
Tactile preceptors
Stained by PAS stain.
MERKEL CELL
Clinical normal areas of mucosa
Nucleated cell layers
Transient
Lymphocytes : Most frequent
Associated with langerhans cells
Polymorphonuclear leukocytes
Mast cells
Inflammatory cells
Lateral Surface Specializations
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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)
Cell junctionsAnother 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.
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.
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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.
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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.
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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.
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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.
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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.
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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.}
Macula adherens (desmosome)
Desmosomes are adhesive intercellular junctions, which are found in tissues subjected to mechanicalstrain.
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.
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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”
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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.
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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.
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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.
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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.
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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
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
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.
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
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