This presentation describes the histology of different types of epithelium, junctional epithelium and its microscopic features and all the histological features of gingiva.
20. The basal cells and the parabasal spinous cells are referred as
stratum germinativum
One population is serrated and
and the other is nonserrated
27. “cornified cell envelope.”
Several proteins contribute to this structure, among which is involucrin.
Involucrin and loricrin ….
Crosslinking of tonofilaments by disulfide bonds facilitates ……
31. cytoskeleton of all epithelial cells along with microfilaments and microfibrils.
Cytokeratins are seen :
Within the cell
desmosomes.
FUNCTIONS:
1. mechanical linkages
2. stress bearing structures
32. K1,K2,K10 to K12 – epidermal type differentiation
K6, K16 – highly proliferative epithelia
K5, K14 – stratification specific
K19 – parakeratinized epithelia
K4, K13 – oesophageal type cytokeratin
34. LANGERHANS CELL
Is intraepithelial immunocompetent clear cells
The cell has a rod-like granules in the cytoplasm, termed Birbeck granules.
It has vimentin-type intermediate filament.
35. play role in protective immunity
These specialized cells process exogenous antigens
antigen specific T lymphocytes
43. Specialized junctions may be classified into:
1. Tight junctions (zonula occludens)
2. Adhesive junctions
a. Cell-to-cell
i. Zonula adherens
ii. Macula adherens (desmosome)
b. Cell-to-matrix
i. Focal adhesions
ii. Hemidesmosomes
3. Communicating (gap) junctions
45. Intercellular junctions typically consist of three components:
1.a transmembrane adhesive protein,
2. a cytoplasmic adapter protein,
3.and a cytoskeletal filament.
46. TIGHT JUNCTIONS
also known as occluding junctions or zonula occludens …..
the major types are
the claudins and the occludins.
48. ADHESIVE JUNCTIONS
or zonula adherens, intermediate junction, or "belt desmosomes’’
hold cells together or anchor cells to the extracellular matrix
50. Adherens junctions are composed of the following proteins:
cadherins.
p120 (sometimes called delta catenin]
γ-catenin or gamma-catenin (plakoglobin)
α-catenin or alpha-catenin
53. CATENIN
The cytoplasmic adapter proteins are members of….
Catenins interact with the cytoplasmic domain of the transmembrane cadherin molecule……
are concentrated on the cytoplasmic side of the cell membrane at the zonula adherens …..
55. DESMOSOMES
In the desmosome, the cadherins are desmoglein and desmocollin.
The catenins are desmoplakin, plakoglobin, and plakophilin, which form an electron-dense plaque ……
57. INTEGRIN
In focal adhesions the transmembrane component is a member of the integrin family….
Integrins are heterodimers of different alpha and beta subunits…..
The cytoplasmic adapter proteins, which include the actin binding proteins α-actinin, vinculin, and
talin,
Binding of the integrin to collagen, laminin, fibronectin results in recruitment and remodeling
58. HEMIDESMOSOMES
link the cell to the basal lamina
The transmembrane adhesive molecules present in hemidesmosomes are the integrin α6β4,laminin,
and collagen XVII the cytoplasmic adapter proteins, bullous pemphigoid antigen 230 (BP230) and
plectin…..
61. Six connexin molecules form a connexon,.
Gap junctions electrically couple cells and allow for a coordinated response to a stimulus by the cells that
are interconnected.
62. epithelium maturation
Cells arising by division in the basal or parabasal ……
maturation in the oral cavity:
keratinization and
nonkeratinization.
66. BASAL LAMINA
consists of :,
lamina lucida, adjacent to the basal cell membrane, and the
lamina densa, between the lamina lucida and the connective tissue.
lamina fibroreticularis,
67. Fibronectin, an adhesive glycoprotein,
type III collagen (reticular fibers),
type VII collagen
atypical basal lamina..
70. LAMININ
Laminin appears to be ubiquitous in basement membrane….
laminin mediates cell adhesion through cell surface integrins……
71. LAMINA PROPRIA
described as a connective tissue….
divided into:
papillary and
reticular.
fine immature argyrophilic (silver staining) reticular fibers……
72. The reticular zone is always present.
The papillary zone may be absent…..
73. the ground substance contains glycoproteins and proteoglycans.
• Hyaluronan, heparan sulfate, versican, decorin, biglycan and
syndecan
The collagen fibers present are of types I and III….
76. REFERENCES
• Clinical periodontology and implant dentistry, JAN LINDHE
• TENCATE,S oral histology 8th edition
• Molecular and cell biology of the gingiva, P.mark Bartold, Laurence J.Walsh and A. Sampath Narayanan
• Kumar GS: Orban’s Oral Histology and Embryology. 13 /e
• Carranza FA.Carranza’s clinical periodontology.11 th edition
Editor's Notes
Histologically, GINGIVA CONSISTS OF two distinct components – the overlying epithelial structures and the underlying connective tissue.
While the epithelium is predominantly cellular in nature, the connective tissue is less cellular and is composed primarily of an integrated network of fibrous and nonfibrous proteins, growth factors, minerals, lipids and water.
The gingival epithelia can be categorized into at least three different types based on their location and composition.
These are epidermal/epithelial cell that synthesizes keratin and its characteristic intermediate filament protein is cytokeratin. Keratinocytes increase in volume in each successive layer from basal to superficial.
Keratinizing oral epithelium has the keratinocytes arranged in four cell layers: basal, spinous, granular, and cornified.
Differentiation During basal cell migration as a keratinocyte it becomes committed to biochemical and morphologic changes.
Differentiation ends with the formation of a keratinized squama, a dead cell filled with densely packed protein contained within a toughened cell membrane.After reaching the surface it is shed or cast off. This process of shedding of surface epithelial cells is called desquamation.
The process of cell migration from the basal layer to the surface is called maturation.
The time taken for a cell to divide and pass through the entire epithelium is termed turnover time or turnover rate.
made up of a single layer of cuboidal cells that synthesize DNA and
undergo mitosis, thus providing new cells.
The basal cells and the parabasal spinous cells are referred to as the
stratum germinativum but only the basal cells can divide.
It has been proposed that the basal cells are made up of two populations. One population is serrated and heavily packed with tonofilaments, which are adaptations for attachment, and the other is nonserrated and is composed of slowly cycling stem cells
The serrated basal cells are a single layer of cuboid or high cuboid cells that have protoplasmic processes (pedicles) projecting, from their basal surfaces toward the connective tissue.Specialized structures called hemidesmosomes, which abut on the basal lamina , are found on the basal surface.They consist of a single attachment plaque, the adjacent plasma membrane, and an associated extracellular structure that appears to attach the epithelium to the connective tissue
The lateral borders of adjacent basal cells are closely apposed and connected by desmosomes.
These are specializations of the cell surface, consisting of adjacent cell membranes and a pair of denser regions (attachment plaques) as well as intervening extracellular structures.The basal cells contain tonofilaments, which course toward, and in some way are attached to the attachment plaques.
The spinous cells which make up this layer are irregularly polyhedral. On the basis of light microscopy, it appears that the cells are joined by “intercellular bridges”Electron microscopic studies have shown that the “intercellular bridges” are desmosomes and the tonofibrils are bundles of tonofilaments
The intercellular spaces of the spinous cells in keratinizing epithelia are large or distended; thus the desmosomes are made more prominent, and these cells are given a prickly appearance.
The spinous (prickle) cells resemble a cocklebur or sticker that has each spine ending at a desmosome.
Of the four layers, the spinous cells are the most active in protein synthesis.
This layer is named for the basophilic keratohyalin granules.
The nuclei show signs of degeneration and pyknosis.
Tonofilaments are more dense in quantity and are often seen associated with keratohyalin granules.
The cell surfaces become more regular and more closely applied to adjacent cell surfaces.
At the same time the lamellar granule, a small organelle (also known as keratinosome, Odland body or membrane-coating granule) forms in the upper spinous and granular cell layers.
The membrane coating granules are glycolipids.
It has an internal lamellated structure. Lamellar granules discharge their contents into the intercellular space forming an intercellular lamellar material, which contributes to the permeability barrier .
This barrier forms at the junction of granular and cornified cell layers.
At approximately the same time during differentiation, the inner unit of the cell membrane thickens, forming the “cornified cell envelope.”
Several proteins contribute to this structure, among which is involucrin.
Involucrin and loricrin become crosslinked by enzyme transglutaminase to form a thin (10 nm) highly resistant electron dense cornified envelope just beneath the plasma membrane.
Crosslinking of tonofilaments by disulfide bonds facilitates close packing of the filaments and gives mechanical and chemical resistance to this layer.
The stratum corneum is made up of keratinized squamae,which are larger and flatter than the granular cells.
Here all of the nuclei and other organelles such as ribosomes and mitochondria have disappeared. The layer is acidophilic (red staining with hematoxylin and eosin) and is histologically amorphous.
The keratohyalin granules have disappeared
The cells of the cornified layer are composed of densely packed filaments developed from the tonofilaments, altered, and coated by the basic protein of the keratohyalin granule, filaggrin.
Crosslinking of tonofilaments by disulfide bonds facilitates close packing of the filaments and gives mechanical and chemical resistance to this layer.
Cytokeratins (CK) form the cytoskeleton of all epithelial cells along with microfilaments and microfibrils.
they are seen :
Within the cell
desmosomes.
FUNCTIONS:
1. They serve to provide mechanical linkages to distribute the forces over a wide area.
2.They function as stress bearing structures within the epithelial cell and are important in maintaining cell shape.
Cytokeratin profile reflects both cell type and diiferentiation status in different types and different layers of epithelia.
K1,K2,K10 to K12 – epidermal type differentiation
K6, K16 – highly proliferative epithelia
K5, K14 – stratification specific
K19 – parakeratinized epithelia
K4, K13 – oesophageal type cytokeratin
The epithelium contains a smaller population of cells that do not possess cytokeratin filaments, hence they do not have the ability to keratinize.
They are not arranged in layers and do not form desmosomal attachments with adjacent keratinocytes. They are usually dendritic and appear unstained or clear in the routine hematoxylin and eosin stains.
They are identified by special stains or by immunocytochemical methods
Is intraepithelial immunocompetent clear cells or dendritic cell found in the upper layers of the skin and the mucosal epithelium.
The cell has a convoluted nucleus and characteristic rod-like granules in the cytoplasm, termed Birbeck granules. This cell is free of melanin.
It has vimentin-type intermediate filaments.
In the presence of antigenic challenge by bacterial plaque Langerhans 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
Langerhans cells are that play an important role in protective immunity and generally located in the stratum spinosum. These specialized cells process exogenous antigens and present them to antigen specific T lymphocytes that, in turn, become activated.
During inflammation, quantitative and qualitative changes to the gingival epithelial Langerhans cells may occur.
originate from neural crest cells , are found in the stratum basale of the gingival oral epithelium.
Each melanocyte establishes contact with about 30–40 keratinocytes through their dendritic processes.
Cells have long dendritic processes that are found interspersed between the keratinocytes of the epithelium and produce considerable amounts of melanin.
Merkel cells are located in clusters at the tips of rete ridges of gingival oral epithelium .
Their origin remains controversial, with reports suggesting origins from either neural crest cells or epithelial sources.
These cells form close associations with intraepithelial nerve endings, forming the epidermal Merkel cell–neurite complexes.
The term zonula describes a junction that completely encircles the cell;
Macula indicates a junction that is more circumscribed in extent.
Tight junctions, also known as occluding junctions or zonula occludens are multiprotein junctional complex.
There are at least 40 different proteins composing
the tight junctions, the major types are
the claudins and the occludins.
Tight junctions control the passage of material through the intercellular spaces.
They also have an important role as a “fence” to define and maintain the two major domains of the cell membrane, the apical and basolateral surfaces.
Adherens junctions (or zonula adherens, intermediate junction, or "belt desmosome" are protein complexes that occur at cell–cell junctions in epithelial, usually more basal than tight junctions.
Adhesive junctions hold cells together or anchor cells to the extracellular matrix the intercellular space in cell-cell adhesive junctions is maintained at approximately 20 nm.
Adhesive junctions are important in cellular signaling.
Their cytoplasmic components may interact with the cytoskeleton, triggering changes in cell shape or motility, or with certain tumor suppressor molecules, or they may act as nuclear transcription factors or coactivators.
Adherens junctions are composed of the following proteins:
cadherins. The cadherins are a family of transmembrane proteins that form homodimers in a calcium-dependent manner with other cadherin molecules on adjacent cells.
p120 (sometimes called delta catenin) binds the juxtamembrane region of the cadherin.
γ-catenin or gamma-catenin (plakoglobin) binds the catenin-binding region of the cadherin.
α-catenin or alpha-catenin binds the cadherin indirectly via β-catenin or plakoglobin and links the actin cytoskeleton with cadherin.
In cell-cell adhesive junctions the principal transmembrane proteins are members of the cadherin family.
Cadherins are calcium ion–dependent proteins that interact homotypically with cadherins on the adjacent cell.
The cytoplasmic adapter proteins are members of the catenin family.
Catenins interact with the cytoplasmic domain of the transmembrane cadherin molecule, with the cytoskeleton, and with a number of other proteins, including kinases, and tumor suppressor molecules that are associated with adhesive junctions.
The catenins and actin filaments are concentrated on the cytoplasmic side of the cell membrane at the zonula adherens to form a dense web that is continuous with the terminal web of actin at the apical (and sometimes the basal) end of the cells
Another transmembrane adhesive protein present in the adherens junction is nectin, a member of the immunoglobulin superfamily.
Nectin has an important role during junction formation, establishing the initial adhesion site and recruiting E-cadherin and other proteins to the junction.
In the desmosome, the cadherins are desmoglein and desmocollin.
The interaction of these transmembrane proteins with those from
the adjacent cell results in a dense line in the middle of the
intercellular space at the desmosome.
The catenins are desmoplakin, plakoglobin, and plakophilin, which form an electron-dense plaque on the cytoplasmic side of the desmosome.
This plaque serves as an attachment site
for the cytoskeletal components,which in the case of the desmosome are intermediate filaments.
In focal adhesions the transmembrane component is a member of the integrin family of adhesion molecules.
Integrins are heterodimers of different alpha and beta subunits that occur in different combinations with specificity for various extracellular matrix molecules.
The cytoplasmic adapter proteins, which include the actin binding proteins α-actinin, vinculin, and talin, link the transmembrane integrins to the actin cytoskeleton.
Binding of the integrin to collagen, laminin, fibronectin, and other extracellular matrix proteins results in recruitment and remodeling of the actin cytoskeleton.
Hemidesmosomes link the cell to the basal lamina and, through additional extracellular molecules, to the rest of the extracellular matrix.
The transmembrane adhesive molecules present in hemidesmosomes are the integrin α6β4, which binds specifically to the basal lamina glycoprotein laminin, and collagen XVII [17 ]the cytoplasmic adapter proteins, bullous pemphigoid antigen 230 (BP230) and plectin, form a dense plaque on the cytoplasmic surface of the hemidesmosome, which functions as an attachment site for intermediate filaments.
Gap junctions are plaque-like regions of the cell membrane where the intercellular space narrows to 2 to 3 nm and transmembrane proteins of the connexin family form aqueous channels between the cytoplasm of adjacent cells.
These proteins have specific tissue and cellular distributions and confer differing permeability properties to the gap junctions.
Six connexin molecules form a connexon,
which has a central channel approximately 2 nm in diameter.
The connexons in one cell pair with connexons
in the adjacent cell to create a patent channel.
Gap junctions electrically couple cells and allow for a coordinated response to a stimulus by the cells that are interconnected.
Cells arising by division in the basal or parabasal layers of the epithelium undergo a process of maturation as they are passively displaced toward the surface.
In general, maturation in the oral cavity follows two main patterns: keratinization and nonkeratinization.
The epithelial surface of the masticatory mucosa (e.g., that of the hard palate and gingiva and in some regions of specialized mucosa on the dorsum of the tongue) is inflexible, tough, resistant to abrasion, and tightly bound to the lamina propria.
It is covered by a layer of keratinized cells, and the process of maturation leading to its formation is called keratinization or cornification.
The basal lamina has an overall thickness of 50 to 100 nm and consists of two structural components, the
lamina lucida,lies adjacent to the basal cell membrane, and the
lamina densa, lies between the lamina lucida and the connective tissue.
In epithelia, there is a third layer, the lamina fibroreticularis, closely associated with the lamina densa. The main constituents of the basal lamina are type IV collagen, which forms a “chicken-wire” network; the adhesive glycoprotein laminin; and a heparan sulfate proteoglycan.
Fibronectin, an adhesive glycoprotein, type III collagen (reticular fibers), type VII collagen (anchoring fibrils) and other types of collagen all made by fibroblasts are present in the lamina fibroreticularis and help maintain the attachment of the basal lamina to the underlying connective tissue
There exists also a special, atypical basal lamina between the ameloblasts and maturing enamel, and between the gingival and the tooth surface.
Type IV collagen is a major component of basement membranes. It is found mainly in the lamina densa, and also within the anchoring plaques of the reticular layer.
Laminin and type IV collagen promote epithelial cell growth.
Basement membranes promote differentiation
The basement lamina facing the tooth surface is termed the internal basal lamina, while that facing the gingival connective tissue is termed the external basal lamina.
Laminin appears to be ubiquitous in basement membranes and, in conjunction with nidogen (entactin), forms an important complex within the matrix.
Laminin is composed of three polypeptide chains which aggregate in a crucifix-like structure.
laminin mediates cell adhesion through cell surface integrins (in particular a6b1) and may also play a regulatory role in cell proliferation and migration of epithelial cells.
With nidogen acting as an intermediary agent, laminin is able to interact with type IV collagen and contribute to the sieve-like network organization of basement membranes.
The lamina propria may be described as a connective tissue of variable thickness that supports the epithelium.
It is divided for descriptive reasons into two parts—papillary and reticular.
The papillary portion is between the epithelial ridges and the
reticular portion is below it.
The reticular layer was thought to contain fine immature argyrophilic (silver staining) reticular fibers. The reticular layer contains netlike arrangement of collagen fibers.
The interlocking arrangement of the connective tissue papillae and the epithelial ridges and the even finer undulations
and projections found at the base of each epithelial cell.
The reticular zone is always present.
The papillary zone may be absent in some areas such as the alveolar mucosa when the papillae are either very short or lacking increases the area of contact between the lamina propria and Epithelium. This additional area facilitates exchange of material between the epithelium and the blood vessels.
In the epithelium , the ground substance in the lamina propria contains glycoproteins and proteoglycans.
Hyaluronan, heparan sulfate, versican, decorin, biglycan and
syndecan are the important proteoglycans present.
Apart from fibroblasts, mast cells and macrophages are present in the connective tissue.
The collagen fibers in the lamina propria are of types I and III. The presence of elastic fibers in the lining mucosa helps to restore tissue form after stretching
Gingiva forms an inevitable part of the periodontium. It supports the teeth and aids in maintaining the integrity of the teeth in function. The gingival tissues, with their specialized relationship to the tooth surface, constitute a major peripheral defense against microbial infections.
