Microscopic Features

The gingiva consists of a central core of connective tissue covered !>\ stratified squamous epithelium. I hese two tissues will he considered separately/

Gingival Epithelium

General Aspects of Gingival Epithelium Biology

Although it constitutes a continuous lining of stratified squamous epithelium, three different areas can be defined from the morphologic and functional points ol view: the oral or outer epithelium, sulcular epithelium, and junctional epithelium.

é A detailed description of gingival histology can he found in Sthroeder HF: The Periodontium, New York, Springer-Vertag, 1986; .met in Biological structure of the normal and diseased periodontium, Periodontology 2000 199/; (13).

Ihe principal cell type of the gingival epithelium, as well as of other stratified squamous epithelia, is the keratinoeyte. Other cells found in the epithelium are the clear cells or nonkeratinocytes, which include the Langerhans cells, Merkel cells, and melanocytes.

Ihe main function ol the gingival epithelium is to protect the deep structures while allowing a selective interchange with the oral environment this is achieved by proliferation and differentiation of the keratinocytc.

Proliferation of keratinoevtes takes place by mitosis in the basal layer and less frequently in the suprabasal lasers, where a small proportion of cells remain as ,i protil-erative compartment while a larger number begins to migrate to the surface.

Differentiation involves the process ol keratinization, which consists of a sequence of biochemical and mor phologic events that occur in the cell as it migrates from the basal layer d'ig. 1-9). The main morphologic change is a progressive flattening of the cell with an increasing prevalence of tonofilamcnts and intercellular junctions coupled to the production of keratohyaline granules and the disappearance of the nucleus. (See Si hroeder'M for further details.)

A complete keratini/ation process leads to the production of an orthokeratinizvd superficial horns layer simitar to thai of the skin with no nuclei in the stratum corneum and a well-defined stratum granulosum dig. I-Id). Only some areas of the outer gingival epithelium are orthokera-tinized; the other gingival areas are covered by parakera-tinized or nonkeratinized epithelium.considered to be

Stratum granulosum

Stratum spinosum

Gambar Tonofibril Stratum Spinosum

Desmosome

Lamellated granules

Tonofibrils Golgi complex

Intercellular space

Lipid droplet

Keratohyaline

Basement membrane

Mitochondria

Granular endoplasmic reticulum

Fig. 1 9 Diagram showing representative cells from the various layers of stratified squamous epithelium as seen by electron microscopy. (Modified from Weinstock A. In: Ham AW: Histology, ed 7. Philadelphia, |B I ip-pmcolt, 1974.)

Desmosome

Stratum granulosum

Lamellated granules

Stratum spinosum

Tonofibrils Golgi complex

Intercellular space

Stratum corneum

Lipid droplet

Keratohyaline

Basement membrane

Stratum basale

Mitochondria

Granular endoplasmic reticulum

Fig. 1 9 Diagram showing representative cells from the various layers of stratified squamous epithelium as seen by electron microscopy. (Modified from Weinstock A. In: Ham AW: Histology, ed 7. Philadelphia, |B I ip-pmcolt, 1974.)

Stratified Squamous Electron Micrograph

! (j I 10 A, Scanning electron micrograph of keratinized gingiva showing the flattened keratinocytes and their boundaries on the surface ot the gingiva ( 1000) B, Scanning electron micrograph of gingival margin at edge o1 gingival sulcus showing at close-up view several keratinocytes about to be exfoliated ( 3000). (From Kaplan OB, Pameijer CH, Ruben MP Scanning electron microscopy ot sulcular and junctional epithe-lia correlated with histology (Part Ij. | Periodontol 1977, 48 -146.)

! (j I 10 A, Scanning electron micrograph of keratinized gingiva showing the flattened keratinocytes and their boundaries on the surface ot the gingiva ( 1000) B, Scanning electron micrograph of gingival margin at edge o1 gingival sulcus showing at close-up view several keratinocytes about to be exfoliated ( 3000). (From Kaplan OB, Pameijer CH, Ruben MP Scanning electron microscopy ot sulcular and junctional epithe-lia correlated with histology (Part Ij. | Periodontol 1977, 48 -146.)

lit intermediate stages of keratinization. I hese areas can progress to maturity or dedifferentiate tinder different physiologic or pathologic conditions.

In pimikerot'mi/etl cpitlwliii, the stratum corneum retains pyknotic nuclei and the keratohyalin granules are dispersed, not giving rise to a stratum granulosum. I he nonkcial'mi/.cil epithelium (although cytokeratins are the major component, as in all epithelial has neither granulosum nor corneum strata, and superficial cells have viable nuclei.

hnniunohistochemistr\. gel electrophoresis, and im-nuinoblot techniques have made identification ot the characteristic pattern of cytokeratins possible in each epithelial type. I he keratin proteins are composed ot different polypeptide subunits characterized by their isoelectric points and molecular weights. I hey .ire numbered in «i sequence contrary to their molecular weight. Generally, basal cells begin synthesizing lower molecular weight keratins (such .is Kl(>, 40 kd) and express other, higher molecular weight keratins as they migrate to the surface, kl keratin polypeptide of 68 kd is the main component of the stratum corneum.

Other proteins unrelated to keratins .ire synthesized during the maturation process. The most extensively studied are keititoliniit and inwhicr'm, which are precursors ot a chemically resistant structure (the envelope) located below the cell membrane, and fikiggrin, whose precursors .ire packed into the keratohyalin granules. In the sudden transition to the horny layer, the keratohyalin granules disappear and give rise to lilaggrin, which forms the matrix ol the most differentiated epithelial cell, the Cometh ilc.

Thus in the fully differentiated state, the corneocytes are mainly formed by bundles ol keratin tonofilaments embedded in an amorphous matrix ol lilaggrin and surrounded In a resistant envelope under the cell membrane. I he iinmunphistochcmical patterns ot the different keratin types, envelope proteins, and lilaggrin, change under normal or pathologic stimuli, modifying the keratinization process."*1

Electron microscopy reveals that keratinocytes are interconnected by structures on the cell periphery called ilesmosomcs."'' These desmosomes have a typical structure consisting of two dense attachment plaques into which tonofibrils insert and an intermediate, electron-dense line in the extracellular compartment. Ionofilaments, which are the morphologic expression of the cvtoskeleton of keratin proteins, radiate in brushlike fashion from the attachment plaques into the cytoplasm of the cells. The space between the cells shows cytoplasmic projections resembling microvilli that extend into the intercellular space and often inlerdigitate.

Less frequently observed forms of epithelial cell connections are tight ¡unctions i/oiiac occhulciis), where the membranes of the adjoining cells are believed to he fused.1 l4Alt Kvidence suggests that these structures allow ions and small molecules to pass from one cell to another.

Cytoplasmic organelle concentration varies among different epithelial strata. Mitoc hondria are more numerous in deeper strata and decrease toward the surface of the cell. Ucordingly, histochemical demonstration of succinic dehydrogenase, nicotinamide-adenine dinu-cleotide, cytochrome oxidase, atid other mitochondrial enzymes revealed a more active tricarboxylic cycle in

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  • graziella
    What does stratified squamous epithelium look like under the microscope?
    8 years ago

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