ULTRASTRUCTURE OF GINGIVA

GINGIVA GINGIVA It is that part of

oral mucosa that covers the alveolar processes of jaw and surrounds the necks of teeth

Clinically,Clinically,

Gingiva is divided clinically into:

Marginal gingivaAttached gingiva Interdental

gingivaGingival sulcus

Ultrastructurally,Ultrastructurally,

Gingiva is composed of

Overlying stratified squamous epithelium

Central connective tissue core

THE EPITHELIUM THE EPITHELIUM

Gingival epithelium is composed of stratified squamous epithelium( flat scale like cells with lumen and arranged in layers)

It consists of constantly renewing cell population in which cell produced are just sufficient to match those lost by desquamation at the surface

lumen

FUNCTIONS OF EPITHELIUMFUNCTIONS OF EPITHELIUM

Protective covering for the tissues beneath and a barrier to entry of foreign material and micro-organisms.

Active role in innate host defense by responding to bacteria in interactive manner.

Signaling functions

PARTS OF EPITHELIUMPARTS OF EPITHELIUM

Functionally and morphologically epithelium is divided into:

Oral epithelium- which faces oral cavity Oral sulcular epithelium- which faces

tooth without being in contact with it Junctional epithelium- which provides

contact between gingiva and tooth.

ULTRASTRUCTURE OF EPITHELIUMULTRASTRUCTURE OF EPITHELIUM

The epithelium covering gingiva is stratified squamous i.e. the cells are arranged in layers in which the cells arising in the basal region undergo a process of differentiation to form a protective surface layer. The surface layers may have different patterns but similar pattern of differentiation can be recognized in basal layers.

EPITHELIAL PROLIFERATIONEPITHELIAL PROLIFERATION

The progenitor cells are situated in basal layer. Dividing cells tend to occur in clusters that are

seen more frequently at the bottom of epithelial ridges

These clusters of cells contain two types of cells

(i) small population of stem cells which retain proliferative potential of tissue.

(ii) larger population of amplifying cells which increase number of cells available for subsequent maturation.

The control of cell division is thought to be brought by locally produced tissue hormones called as CHALONES. These are produced by post-mitotic epithelial cells and have dual property of stimulating cell differentiation and inhibiting mitosis.

Various cytokines affect cell division and proliferation like epidermal growth factor, keratinocyte growth factor, IL-1, TGF-α and β

Other factors affecting cell division are adrenaline, stress, age, diurnal rhythm.

Turnover time of epithelium varies from 5- 57 days.

ULTRASTRUCTURE OF EPITHELIAL CELL ULTRASTRUCTURE OF EPITHELIAL CELL

Cells of basal layer are least differentiated oral epithelial cells. They contain not only organelles like mitochondria, ribosomes, endoplasmic reticulum and golgi complexes but also contains certain characteristic structures that identify them as epithelial cells and distinguish them from other cell types. These structures are:

Filamentous structures called as tonofilaments

Intercellular bridges or desmosomes.

TONOFILAMENTS- are fibrous proteins synthesized by the ribosomes and are seen as long filaments.

Diameter is approximately 8nm. Chemically, they are a class of intracellular

proteins known as cytokeratins which are characteristically present in epithelial tissues.

These are classified according to their size and charge.

These become aggregated to form bundles of filaments called as tonofibrils.

Due to presence of these keratin filaments epithelial cells are also called as “ keratinocytes”

Keratins represent 30 different proteins of differing molecular weights.

Those with the lowest molecular weight (40 kDa) are found in glandular and simple epithelia.

Those with intermediate molecular weight are present in stratified epithelia.

Those with highest molecular weight( 67 kDa) in keratinized stratified epithelium.

All stratified oral epithelia possess keratins 5 and 14

Keratinized oral epithelium contains 1, 6 ,10 and 16

Non keratinized epithelium 4, 13 and 19 Other proteins unrelated to keratins synthesized

in cell are KERATOLININ AND INVOLUCRIN. They are precursors of chemically resistant structures located below cell membrane and FILAGGRIN which form matrix of corneocyte.

EPITHELIAL MATURATIONEPITHELIAL MATURATION

The cells arising by division in basal layer undergo a maturation process as they move to surface.

Maturation follows two patterns: (i) Keratinized (ii) Non- keratinized

KERATINIZATION This process leads to formation of epithelium

which is inflexible, tough, resistant to abrasion and tightly bound to underlying connective tissue.

LAYERS OF KERATINIZED EPITHELIUM STRATUM BASALE- the basal layer in this

pattern is composed of cuboidal or columnar cells adjacent to basement membrane. This layers consists of cells which divide and proliferate subsequently

STRATUM SPINOSUM- this layer consists of larger elliptical or spherical cells which shrink away from each other remaining in contact at certain points only giving it a spike or prickle

type appearance So, also called as “prickle cell” layer Upper layer contains dense granule

“keratinosomes or Odland bodies”. They are modified lysosomes

STRATUM GRANULOSUM- it consists of larger flattened cells .

The cells typically consist of granules called as “keratohyaline granules”

STRATUM CORNEUM- it is the surface layer composed of flat (squamous) cells.

The uppermost layer is cornified or horny.

This process of keratinization forms two patterns.(i)orthokeratinization (ii)parakeratinization

This process of keratinization forms two patterns.(i)orthokeratinization (ii)parakeratinization

ORTHOKERATINIZEDUppermost layer do not

contain any nucleiStratum granulosum

has more no of keratohyaline granules

PARAKERATINIZEDUppermost layer

contains pyknotic nuclei

The keratohyaline granules are less in number and dispersed

NON- KERATINIZED Basal and prickle cell layers are same No sudden changes in cell morphology is

observed above stratum spinosum. The outer half of tissue is divided into two

arbitrary zones STRATUM INTERMEDIUM STRATUM SUPERFICIALE Granular layer is absent Superficial layer consists of nuclei. This pattern leads to formation of flexible, soft

epithelium

NON-KERATINIZED EPITHELIUM

Important property of any epithelium is its ability to function as a barrier which depends on close contact or cohesiveness of epithelial cells.

Cohesion between cells is provided by a viscous intracellular material consisting of protein- carbohydrate complexes produced by epithelial cells themselves.

In addition, modifications of adjacent cell membranes of cells occur. Main are

1. Occluding junctions (zonula occludens) 2. Adhesive junctions (a) cell to cell (i) zonula adherens (ii) macula

adherens(desmosomes) (b) cell to matrix (i) focal adhesions (ii) hemidesmosomes 3. Communicating (gap) junctions

TIGHT JUNCTIONS- the opposing cell membranes are held in close contact by the presence of transmembrane adhesive proteins (occludin, claudin ) arranged in anastomosing strands that encircle the cell.

They control the passage of material through intercellular spaces

ADHESIVE JUNCTIONS- Intercellular space is 20 nmADHESIVE JUNCTIONS- Intercellular space is 20 nm

ZONULA ADHERENSJunction that completely

encircles cellsTransmembrane proteins

are E-cadherin and catenin of cadherin family

MACULA ADHERENS

Junction that is circumscribed (spot like)

Transmembrane proteins are desmoglein and desmocollin of cadherin family

COMMUNICATING OR GAP JUNCTIONS These are plaque like regions of cell membrane

where intercellular space narrows to 2-3 nm. Transmembrane proteins are of connexin family These junctions have electrically coupled cells

and allow for coordinated response to a stimulus by cells that are interconnected.

NON-KERATINOCYTES IN ORAL EPITHELIUM

NON-KERATINOCYTES IN ORAL EPITHELIUM

Apart from keratinocytes oral epithelium contains cells that differ in appearance from other keratinocytes in having a clear halo around their nuclei so, are termed as CLEAR CELLS or NON-KERATINOCYTES.

These cells make 10% of total cell population. These cells are MELANOCYTES LANGERHANS’ CELLS MERKEL CELLS INFLAMMATORY CELLS

MELANOCYTES- These cells arise embryologically from neural crest ectoderm.

Present in basal layer and produce melanin, the color pigment.

Melanin is produced in melanosomes and then inoculated into cytoplasm of adjacent keratinocytes

These cells lack desmosomes and tonofilaments but have long dendritic process extending between keratinocytes.

LANGERHANS’ CELLS- present in suprabasal layers

Dendritic in nature No desmosomes or tonofilaments. Antigenic in nature. Contain small rod or flask shaped

granules called as birbeck’s granules.

MERKEL CELLS- present in basal layer. No desmosomes and tonofilaments. Unlike the other two cells, it is not dendritic in

nature. Contains small granules which may liberate

transmitter substance across the synapse- like junction between cell and nerve fibre thus triggering an impulse.

So they are supposed to be sensory and they respond to touch

INFLAMMATORY CELLS-seen transiently in between nucleated cell layers.

Most commonly seen are lymphocytes. Others are neutrophils and mast cells.

LYMPHOCYTE NEUTROPHIL MAST CELL

JUNCTION OF EPITHELIUM AND CONNECTIVE TISSUE

JUNCTION OF EPITHELIUM AND CONNECTIVE TISSUE

The region where the epithelium and underlying connective tissue meet appears as an undulating interface at which papillae of connective tissue interdigitate with epithelial ridges

Ultrastructurally, this region is called as basal lamina and is highly organized.

This structure along with hemidesmosomes attaches epithelium to C.T. Also there are some focal adhesions presnt.

HEMIDESMOSOMES FOCAL ADHESIONS

Basal lamina act as filter to contro passage of molecules.

It also has signaling functions essential for epithelial differentiation

It has an overall thickness of 50 to 100 nm. Has two structural components called as

lamina lucida adjacent to epithelium and lamina densa adjacent to connective tissue.

Main constituent is type IV collagen , adhesive glycoprotein laminin and fibronectin.

Also contains type III ( reticular fibres ) and type VII ( anchoring fibrils ) collagen

LAMINA PROPRIA LAMINA PROPRIA

The connective tissue supporting the oral epithelium is termed as LAMINA PROPRIA.

Divided in two layers: PAPILLARY LAYER RETICULAR LAYER Lamina propria consists of cells , blood vessels

neural elements and fibres embedded in amorphous ground substance.

Shows regional variation.

PAPILLARY LAYER RETICULAR LAYER-It is the superficial layer - It is the deeper layer-Collagen fibres are thin - Fibres are arranged inand loosely arranged. thick bundles and tend to lie parallel tosurface plane.

CELLS OF CONNECTIVE TISSUEThe lamina propria contains several different

cells like fibroblasts , macrophages, mast cells and inflammatory cells.

FIBROBLAST It is the principle cell present. Is responsible for elaboration and turnover of

fiber and ground substance thus playing a key role in maintaining tissue integrity.

It is fusiform or stellate shaped cell with a long process that lie parallel to bundles of collagen fibres

Is an active synthetic cell that contains numerous mitochondria, extensive granular endoplasmic reticulum, prominent golgi complex and numerous

membrane bound vesicles. Have a low rate of proliferation except in

healing phases.

MACROPHAGES It is also a stellate shaped cell so difficult to

distinguish from fibroblast Smaller and denser nuclei and less granular

endoplasmic reticulum Cytoplasm contains membrane bound

vesicles that can be identified as lysosomes.

Principal function is phagocytosis which is important as it increases the antigenicity before it is presented to lymphocytes for immunologic response.

MAST CELL Large spherical or elliptical

mononuclear cell These cells are present in relation to

blood vessels so they play a role in maintaining normal tissue stability and vascular homeostasis.

INFLAMMATORY CELLS Lymphocytes and plasma cells can be

seen scattered throughout the lamina propria in small numbers normally

Their number increase during injury and according to nature of injury.

FIBRES AND GROUND SUBSTANCE The intercellular matrix of lamina propria

consists of two major types of fibres COLLAGEN ELASTIC FIBRES

COLLAGEN It constitutes the most abundant proteins

found in the body The collagen family consists of atleast 30

different genes, which produce 19 known types of collagens

STRUCTURE OF COLLAGEN All collagens are composed of three polypeptide

alpha chains coiled around each other to form typical collagen triple-helix configuration.

Common features include amino acid GLYCINE in every third position, high proline residues and presence of hydroxylysine and hydroxyproline.

Are classified according to structure as1. Fibrillar collagens( TYPES I, II , III, V and XI) These are fibrils forming collagens They show typical 64 nm banding pattern Type I collagen is most abundantly found collagen. Type II is found in cartilage Type III is found in granulation tissue. Type V is found associated with type I and III and

type XI is found associated with type II.

2. FIBRIL ASSOCIATED COLLAGENS (type IX, XII,XIV)

These are collagens with interrupted triple helices i.e. consist of chains that have different lengths and contain a variety of non-collagenous domains.

IX is associated with type II and the other two with type I.

These collagens are believed to modulate interactions between adjacent fibrils.

3.MESHWORK FORMING COLLAGENS (TYPE VIII and X)

Type VIII is associated with basal laminae Type X is found in epiphyseal growth plate.

They are believed to impart compressive strength while providing open porous network.

ANCHORING FIBRIL COLLAGEN (type VII) It extend from basal lamina to underlying

connective tissue.

MICROFIBRIL FORMING COLLAGEN (TYPE VI) This collagen binds cells, proteoglycans and

type I collagen and act as a bridge between them.

TRANSMEMBRANE COLLAGEN (TYPE XIII and XVII)

Help in cell- matrix adhesion

ELASTIN FIBRES These are rubber like protein produced by

fibroblasts and smooth muscle cells. The elastic properties are due to numeous

intermolecular cross- links between lysine groups, formed by enzymes lysyl oxidase .

Glycoproteins fibrillin 1 and 2 and microfibrils are required.

In absence of elastin they are called as oxytalan fibres

Developing elastic fibres are called as elaunin fibres

GROUND SUBSTANCE Ground substance of extracellular matrix

consists of complex mixture of macromolecules.

These macromolecules interact with cells and the fibrous components of the matrix and are involved in adhesion and signaling events.

The ground substance is highly hydrated which helps in regulating tissue water content and diffusion of nutrients, waste products and other molecules

Fibroblasts synthesize two main classes of macromolecules making up ground substance – proteoglycans and glycoproteins

Proteoglycans are large group of cell surface associated molecules that consists of protein core to which glycosaminoglycan chains are attached

Their important property is to bind growth factors, cytokines and other biologically active molecules.

GLYCOPROTEINS Major are fibronectin, tenascin,thrombospondin They are majorly involved in attachment spreading

and migration of cells and organization of collagen fibrils.

GROWTH FACTORS AND CYTOKINES Fibroblasts secrete number of growth factors,

cytokines and inflammatory mediators like IL-1, IL-6, IL-8, TNF-α, PDGF, keratinocyte growth factor etc.

These have important roles in developmental processes, wound healing and tissue remodelling.

GROUND SUBSTANCE

MICROCIRCULATION OF GINGIVAMICROCIRCULATION OF GINGIVA

Microcirculatory tracts, blood vessels and lymphatic vessels play an important role in drainage of tissue fluid and in spread of inflammation.

Microcirculation can be evidenced by: Immunhistochemical reactions Histoenzymatic reactions Perfusion of dyes Scanning electron microscopy Laser doppler flowmetry

Sources of blood supply SUPRAPERIOSTEAL ARTERIOLES- along facial and

lingual surfaces of alveolar bone, from which capillaries extend along the sulcular epithelium and between rete pegs of external gingival surface.

VESSELS OF PERIODONTAL LIGAMENT- extend into gingiva and anastomose with capillaries in sulcus area.

ARTERIOLES- emerge from crest of interdental septa and extend parallel to crest of bone, then forming anastomosis with other capillaries.

Beneath the epithelium the capillaries extend in papillary connective tissue in the form of terminal hair pin loops.

LYMPHATIC drainage of gingiva brings in the lymphatics of connective tissue papillae .it progresses into the collecting network external to the periosteum of alveolar processes , then to regional lymph nodes , particularly submaxillary lymph node group

Lymphatics beneath the junctional epithelium extend into the periodontal ligament and accompany the blood vessels