Lec. 16 Dr. Ali H. Murad Oral mucous membrane The oral cavity lined by a mucosa called oral mucosa. This composed of 2 structures. a- Surface epithelium layer b- Underlying connective tissue. A- Epithelium: The epithelium of the oral cavity is of the stratified squamous. & it divided into three major types. 1- Masticatory mucosa (keratinized mucosa): This type attached to bone & does not stretch. & it bears the forces of mastication, it cover the gingiva & hard palate. This type has 4 cells layers: A- Basal layer (stratum basale): It is consist of a single layer of cuboidal cells that attached with the connective tissue by protoplasmic processes known as Hemidesmosome. & attached with each other's by desmosome. These cells undergo mitotic activity, in which one cell remain in the basal layer & other differentiated & replace each cell that desquamates 1 B- Spinous layer (stratum spinosum): Are irregular polyhedral & larger than the basal cells. & joined with each other by intercellular bridges (desmosome), with large intercellular spaces & the desmosomes are prominent, given a prickle appearance. C- Granular layer (stratum granulosum): The cells in this layer are larger (flatter & wider) than the spinous cells. In this layer the cell surface become more regular & it contain small organelle (lamellar granules). D- Cornified layer (stratum corneum): Is made up of keratinized squamous, which are larger & flatter than the granular cells. This layer of 2 types: 1- Parakeratinized: in which the cells contain a pyknotic & condensed nuclei. 2- Orthokeratinized: in which the cells empty. 2- Lining mucosa (non-keratinized mucosa): This type covers the musculature & is distensible, adapting itself to the contraction & relaxation. 2 It covers the lip, cheek, floor of mouth, soft palate, vestibule, & alveolar mucosa (these areas not exposed to the forces of mastication. This type has 3 cell layers: 1- Basal layer (stratum basale): similar to that of keratinized mucosa. 2- Intermediate layer (stratum intermedium): are larger than the cells of the stratum spinosum, with smaller intercellular spaces, & do not have a prickly appearance. 3- Superficial layer (stratum superficiale): this layer resemble the stratum granulosum in keratinized mucosa, but it’s contents are granular rather than lamellar & smaller or vestigial granules. N.B.: there is no stratum corneum in non-keratinized oral mucosa. 3- Specialized mucosa: It is so-called because it bears the taste buds, it cover the dorsum of the tongue. 3 B- Connective tissue: This layer immediately below the epithelium, it composed of 2 layers: 1- Lamina propria: It is that part of connective tissue of variable thickness that supports the epithelium. It composed of the papillary layer & deeper reticular layer. 2- Submucosa: This layer of connective tissue beneath the lamina properia, & it attaches the mucous membrane to the underlying structures. Whether this attachment is loose or firm. The submucosa contains glands, blood vessels, nerves, lymphatics & adipose tissue. General consideration -The papillae of the connective tissue protrude toward the epithelium, carrying blood vessels & nerves. -The epithelium also formed into ridges that protrude toward the lamina propria & these ridges interdigitates with the papillae & are called epithelial 4 ridges. -The epithelium does not contain blood vessels. -The larger arteries in the submucosa divided into smaller branches, which then enter the lamina propria, & then again divide to form a subepithelial capillary network in the papillae. -The veins originating from the capillary network course back along the path taken by the arteries. -The cells of the epithelium layer originated from the basal layer (by mitotic activity), then migrates pushed upward until reaching the surface, it become dead cell & desquamates. This migration from the basal cell layer to the surface & desquamation known as epithelial turnover. -In general nonkeratinized oral mucosa have higher rates of mitosis than the keratinized oral mucosa. 5 .