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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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