Oral Mucosa Dr Jamal Naim PhD in Orthodontics Cont. 1
Last session • Definition of oral mucosa • Functions of the oral mucosa • Protection • Sensation • Secretion • Thermal regulation • Epithelial maturation • Keratinization • Nonkeratinization
Last session • KE: • Stratum basale • Stratum spinosum • Stratum granulosum • Stratum corneum • Non-KE • Stratum basale • Stratum spinosum • stratum intermedium • Stratum superficiale
Ultrastructure in the epithelial cell Keratinocytes is another name of the epithelial cells because they contain keratin (cytokeratin). Cytokeratin is an intracellular protein and is a characteristic component of epithelia; cells. Every epithelial cells contains filamentous strands, the so called tonofiliaments and has intercellular bridges to other EC, the so called desmosomes. Aggregated tonofiliaments are called tonofibrils.
Ultrastructure in the epithelial cell An important property of any epithelium is to function as a barrier, which depends on the great extent of the close contact of epithelial cells. The most common contact type between epithelial cells is desmosomes. Other types are gap junctions and tight junctions.
A: demosome B: tight junction C: gap junction
Ultrastructure in the epithelial cell Desmosomes (macula adherens) are circular or oval areas of adjacent cell membranes, adhering by specialized thickenings into which bundles of tonofilaments insert.
Ultrastructure in the epithelial cell Adhesion between the epithelium and connective tissue is provided by hemidesmosomes, which are present on the basal membrane of cells of the basal layer. Hemidesmosomes posses also intracellular attachment plaques with tonofilaments inserted.
epithelium Connective tissue
Ultrastructure in the epithelial cell The desmosomes, hemidesmosomes, and tonofilaments together represent a mechanical linkage that distribute and dissipates localized forces applied to the epithelial surface over a wide area.
Ultrastructure in the epithelial cell Gap junctions: also called nexus are regions where adjacent membrans of epithelial cells run closely together, separated by only a small gap. In tight junctions the cell membranes of adjacent cells is so tightly apposed as to exclude intercellular space.
Maturation in the oral epithelium • In keratinized and nonkeratinized epithelium the maturation is accompanied with: • Change in cell size • Change in cell form • Synthesis of more structural proteins in form of tonofilaments • The production additional intercellular material
Maturation in the oral epithelium In both types of epithelia the cells increase in size (more in Non-KE) and migrate from basal cell layer to the prickle cell layer. In the prickle cell layer there is an active synthesis of tonofilaments, which in KE aggregate together to form tonofibrils.
Cells of the prickle cell layer (str. Granulosum in the KE: aggregated tonofilaments to form tonofibrils are seen Cells of the prickle cell layer (str. Granulosum in the Non-KE: the tonofilaments stay dispersed
Maturation in the oral epithelium In the next layer (granular Layer/intermediate layer) the cells are greater in volume but more flattened. They contain the so called membrane coating granules. In the upper part of this layer the granules fuse with the cell membrane to discharge their content into the intercellular space.
Maturation in the oral epithelium In KE the content is lipid rich and form a barrier to limit the movement of aqueous substances. In Non-KE the contents have a different lipid composition and don’t form a barrier as in KE. The cells of the superficial part of the gr. Layer develop a thickening of their cell membrane to form a barrier against chemical solvents.
Maturation in the oral epithelium All other events in maturation are different in KE and Non-KE. Keratinized Epithelium: The most characteristic feature of the granular layer is the keratohyaline granules. It is thought that keratohyaline granules facilitate the aggregation of the tonofilaments.
Maturation in the oral epithelium • As the cells of the gr. Layer reach the junction with the keratinized layer, a sudden change occurs: • All organelles, including the nuclei and keratohyaline granules, disappear • The cells dehydrate • The cells become packed very dense.
Maturation in the oral epithelium In the keratinized layer the cells become more flattened and denser packed. The form of the cells become hexagonal, the so called squames. The squames will be in the process of desquamation lost. The keratinized layer of the oral cavity is the thickest in the body (up to 20 layers) except soles and palms, and so resistant to mechanical and chemical damage.
Maturation in the oral epithelium In the Non-keratinized epithelium the cells of the intermediate layer become less flattened than in the KE. Keratohyaline granules are rare and remain in the next layers. In the superficial layer the cells are more flattend but contains granules, tonofilaments and nuclei. Other cell organelles are diminished.
Maturation in the oral epithelium The surface layer cells are not dehydrated and form a surface that is flexible and tolerant of compression. Hyperkeratosis is forming more or thicker keratinized layer than normal. This can be physiologic in kerainized epithelium (smokers), sometimes also in Non-KE (linea alba), but most hyperkeratosis in Non-KE is pathologic.
Permeability and absorption Unlike the intestinal lining, which is absorptive, the Oral epithelium has the main function to be an impermeable barrier. This barrier consists of lipids derived from the membrane-coating granules in the cells of the granular/intermediate layer. This permeability is different between regions of the oral cavity, thus the mouth floor is the most permeable region.