Oral Mucosa: 23-Oral Mucosa PDF

The Oral Mucosa Oral Biology  The aim of this lecture: Learn the development, structure and function of the oral mucosa and connective tissue Know the types of oral epithelium in different oral regions and associate the structure to function. Familiarize ourselves w...

The Oral Mucosa Oral Biology  The aim of this lecture: Learn the development, structure and function of the oral mucosa and connective tissue Know the types of oral epithelium in different oral regions and associate the structure to function. Familiarize ourselves with the keratinocytes and non- keratinocytes and their clinical considerations thereof. Know the types of oral mucosa lining the surface of the tongue, the different papillae and the taste buds. Appreciate the uniqueness of the gingival structures and understand the concept of crevicular fluid, it´s composition and primary role in health.  Definition Mucous membrane- moist lining of the GI tract, nasal passages and other body cavities communicating with external environment. Oral mucous membrane or oral mucosa is moist lining in the oral cavity Oral mucosa is continuous with the skin (lips area) and with the rest of the gut (pharynx). It locates between the skin and gastrointestinal (GI) tract. Skin, oral mucosa and GI lining share similar components: a covering epithelium and underlaying connective tissue.  Development of oral mucosa Formation of primitive oral cavity (stomodeum fuses to foregut after the rupture of buccopharyngeal membrane (26 days of gestation). Structures develop from branchial arches (tongue, epiglottis, pharynx) are covered by epithelium derived from endoderm. Palatal, buccal, gingival epithelium and epithelium covering the floor of the mouth and lips are ectodermal origin.  Functions 1. Protection 2. Sensation 3. Secretion 4. Thermal regulation  1. Protection Adaptations to withstand compression, Barrier to Immunological defense stretching, shearing, microorganisms, toxins mechanisms: humoral abrasion & bacterial and various antigens. and cell mediated influences  2. Sensation Temperature, Reflex receptors pressure, pain, for swallowing, taste gagging  3. Secretion Maintenance of moist Major salivary glands- Major secretion surface, buffering, their secretion passes produced by salivary secretion of antibodies, through mucosa via glands is SALIVA. viscoelastic mucous film ducts. acts as a barrier. Minor salivary glands are present in submucosa except gingiva and anterior part of hard palate.  4. (Thermal regulation) (In animals like dogs - panting )  Differences between mucosa vs. skin Absence of skin appendages but Hair follicles, sebaceous has salivary glands glands, sweat glands Sometimes ectopic sebaceous glands (Fordyce’s granules) Smoother with less wrinkles Deeply colored https://pocketdentistry.com/ https://www.stanfordchildrens.org  Fordyce granules common soft tissue variation seen in the oral cavity ectopic sebaceous glands characterised by yellowish- white papular lesions scattered throughout the oral mucous membrane more common in the buccal mucosa https://screening.iarc.fr/atlasoral_list.php?cat=I1&lang=1#:~:text=Fordyce%20granules%20or%20papules%20are,common%20in%20the%20 buccal%20mucosa. Figure - available from: Head and Neck Pathology Similarities between skin and oral mucosa Yip, F & Le, Bach. (2019). A Guide to Sutures. Organization of Oral Cavity Outer vestibule Bounded by lips & cheeks Oral cavity proper Separated from vestibule by alveolus bearing teeth and gingiva Superior: Hard and soft palate Inferior: Floor of mouth & tongue base Posterior: Fauces & tonsils ALL LINED BY DIFFERENT TYPES OF MUCOSA  Regional variation of mucosa Due to functional needs, three types of mucosa can be found in mouth: Lining mucosa (60%) Masticatory mucosa (25%) Specialised mucosa (15%)  Mobile & distensible Non-keratinised mucosa Whole mouth except gingiva, hard Regional palate & dorsum of tongue variation of mucosa LINING MUCOSA (60%): Ten Cate’s Oral Histology, 2016  Attached to bone (muco-periosteum) Resist high levels of friction & compression Keratinised type of mucosa Regional Gingiva, hard palate & dorsum of tongue variation See the “yellow” labels below! of mucosa MASTICATORY MUCOSA (25%) Ten Cate’s Oral Histology, 2016 Regional Dorsum of tongue variation Function of taste See the “light pink ” label below! of mucosa SPECIALISED MUCOSA (15%) Ten Cate’s Oral Histology, 2016  Oral Mucosa: Composition Two layers: Overlying epithelium [Epidermis the in skin] Underlying connective tissue (lamina propria) [Dermis in the skin] Basement membrane between epithelium & lamina propria PS: Epithelium & lamina propria interdigitate with rete ridges & connective tissue papillae Ten Cate’s Oral Histology, 2016  Oral Mucosa Composition Lining & Specialised mucosa: Epithelium Lamina propria SUBMUCOSA Masticatory mucosa: Epithelium Lamina propria PERIOSTEUM BONE Ten Cate’s Oral Histology, 2016  Clinical Implications Local anesthetics Surgical suturing Inflammation  EPITHELIUM Cropped image from Ten Cate’s Oral Histology, 2016  Consists of 2 cell populations: Keratinocytes (Squamous or keratinised epithelium) According to the pattern of maturation, epithelium can be divided in: Keratinising epithelium Non-keratinising Epithelium epithelium Non-keratinocytes Melanocytes Langerhans cells Merkel cells Inflammatory cells  Keratinocytes Epithelial cells filled with cytokeratin. Two functional populations of cells: Progenitor cells Divide & provide new cells Maturing cells Undergo differentiation & maturation ORTHOKERATINISATION -pattern of maturation Cropped image from Ten Cate’s Oral Histology, 2016  Keratinocytes Continuous epithelial turnover Cytokines involved: epidermal growth factor, keratinocyte growth factor, IL-1, TGF α & ß Turnover time – time for a cell from dividing in the basal layer to pass through the entire epithelium during maturation PS: Turnover time differs in different areas of oral mucosa (gingiva: 41- 57days; cheek: 25days )  Keratinizing Epithelium Masticatory mucosa (gingiva & palate) Dorsum of tongue Vermillion zone  Keratinising epithelium I Stratum Basale/ germinativum (Basal layer) II Stratum spinosum (Prickle layer) III Stratum granulosum IV Stratum corneum Cropped image from Ten Cate’s Oral Histology, 2016  I Stratum Basale Single layer of cuboidal or columnar cells Situated on basal lamina Progenitor cells of epithelium Only layer where mitotic figures should occur Cell division higher up prevented by unknown mechanism of growth inhibitor factors Cropped image from Ten Cate’s Oral Histology, 2016  Clinical Implications Cancer chemotherapeutic drugs  II Stratum Spinosum (“prickle layer”) Several layers of elliptical cells Synthetic activity No mitotic figures Tonofibrils (cytoskeleton) Cropped image from Ten Cate’s Oral Histology, 2016 Membrane coating organelles (Odland bodies) Stratum Spinosum (“prickle layer”) Desmosomes (‘spiny’ appearance)  Clinical Implications Acanthosis – Hyperplasia of stratum spinosum http://www.nsc.gov.sg/content/445/a3f3.jpg  Cytokeratins (CK) CK are intermediate filaments specific for epithelial cells Different distribution in different types of epithelium http://www.dundee.ac.uk/biocentre/Images /Research/DIV4/elbfig2.jpg  Cytokeratins – Clinical Implication Histopathology of tumour cell lineage http://sarcoma.org/pathology_review/pathology%20introduction/image/cytoker.jpg  III Stratum Granulosum Larger, flatter, mature cells Less organelles Tonofilaments (Cytokeratins) Keratohyaline granules Cropped image from Ten Cate’s Oral Histology, 2016  Stratum Granulosum Keratohyaline granules contains the precursor to the matrix in which the tonofilaments are embedded IV Stratum Corneum Final stage of maturation: keratinised epithelium Several layers of cells Closely packed tonofilaments in matrix protein = KERATIN Loss of all organelles Disappearance of desmosomes Desquamation The function is mechanical protection Cropped image from Ten Cate’s Oral Histology, 2016  Stratum Corneum Two types: Orthokeratinised Loss of all nuclei Parakeratinised Nuclei retained but small & shrunken  Non-Keratinising Epithelium Lining Mucosa Buccal mucosa Labial mucosa Floor of mouth Ventral tongue http://www.infocompu.com/adolfo_arthur/images/estudio14.jpg  Non-Keratinising epithelium Stratum Basale/ germinativum (Basal layer) Stratum spinosum (Prickle layer) Stratum intermedium Stratum superficialis Cropped image from Ten Cate’s Oral Histology, 2016  Cropped image from Ten Cate’s Oral Histology, 2016 Stratum Basale & Spinosum Like keratinising epithelium but cells slightly larger  Stratum Intermedium Slightly flattened cells Tonofilaments dispersed in cytoplasm (not aggregated into bundles like keratinising epithelium) Cells contain nuclei No granular layer Cropped image from Ten Cate’s Oral Histology, 2016 Ten Cate’s Oral Histology, 2003  Stratum Superficialis Slightly flattened cells with dispersed tonofilaments Organelles Nuclei persist Cropped image from Ten Cate’s Oral Histology, 2016  Clinical implication: keratinised and non- keratinised epithelium Hyperkeratosis- physiologic response of keratinised oral epithelium to chronic irritation. (thickening of palatal epithelium of smokers). Hyperkeratosis- physiologic change or associated with abnormal cellular changes of non-keratinised epithelium. Linea Alba-Non-keratinised buccal mucosa develops thin keratin layer along occlusal line. Inflammation reduces degree of keratinisation to the degree that it appears parakeratinised or non-keratinised.  Non- Keratinocytes 10% of cells in epithelial layer Usually appears as ‘clear cells’ on section if stained routinely with H&E. Includes: Melanocytes Langerhans’ cells Merkel cells Inflammatory cells Image from Ten Cate’s Oral Histology, 2016  Melanocytes Pigment-producing cells in the basal layer. Derived from the neural crest cells and present at about 8 weeks IU life. Self-reproducing cell population No desmosomes or tonofilaments http://meded.ucsd.edu/hist-img-bank/chapter_5/Slides_70_and_71_pigmented/images/c.5.71.1.3.jpg  Melanocytes Dendritic processes between keratinocytes Melanin is produced in melanosomes which are then injected into the cytoplasm of adjacent cells  Electron micrograph of melanocyte packed with melanosomes Image from Oral Anatomy, Histology and Embryology by Berkovitz et al. 2018  Clinical consideration Pigmentation of oral mucosa: Physiologic Racial pigmentation Pathologic Neoplasms (melanoma) Black and Brown: Non-neoplastic Pigmentation of the Oral Mucosa - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/a-Diffuse-homogenous-brown-pigmentation-of-the-attached-gingiva-b-Physiologic_fig1_330542777 [accessed 27 May, 2022]  Lack of pigmentation Albinism- due to low production or lack of enzyme called tyrosinase. Autosomal recessive condition Hypopigmentation and vision- related disabilities Langerhans cells Dendritic cells in the layers above Stratum Basale No desmosomes Bone marrow precursors Act as antigen presenting cells www.nurseminerva.co.uk/ diagrams.htm Langerhans cells Immune function (antigen- presenting cells) Hypersensitivity reactions Anti-tumour immunity Propagator of HIV infection transmission to T- cells Can be identified due to ATPase on cell membrane Consist of Birbeck granules.  Merkel cells In basal layer close to nerve fibres Derived from differentiation of an epidermal progenitor. ? sensory function Common in masticatory mucosa, mostly absent from lining mucosa Cytokeratins and occasional desmosomes http://www.merkelcell.org/images/corpusclePic.jpg Inflammatory cells Transient cells that do not reproduce themselves in the epithelium Mostly lymphocytes Normal component of non-keratinocyte population  Oral Mucosa: Composition Two layers: Overlying epithelium [Epidermis in skin] Underlying connective tissue (lamina propria) [Dermis in skin] Basement membrane between epithelium & lamina propria Cropped image from Ten Cate’s Oral Histology, 2016  Oral Mucosa Composition Lining & Specialised mucosa: Epithelium Lamina propria SUBMUCOSA Masticatory mucosa: Epithelium Lamina propria PERIOSTEUM BONE Ten Cate’s Oral Histology, 2016 Oral Mucosa Composition Main components: Overlying epithelium Basement membrane between epithelium & lamina propria Underlying connective tissue (lamina propria) https://pocketdentistry.com/9-oral-mucosa/  Epithelium- Connective tissue interface Epithelium projections into underlying connective tissue: rete ridges Larger interface with stronger binding (length varies with location & function) Interface for metabolic exchange (epithelium have no blood vessels)  Epithelium- Connective tissue interface Epithelium projections into underlying connective tissue: rete ridges Rete ridges are more numerous, longer and thinner in masticatory mucosa than lining mucosa  Epithelium- Connective tissue interface Epithelium and lamina propria meet at basement membrane EM: Rather a basal lamina complex than true membrane: Highly organised area consisting of 2 zones: Lamina lucida immediately underneath epithelium Lamina densa Lamina fibroreticularis  Ten Cate’s Oral Histology, 2016 Lamina lucida: 45nm glycoprotein layer Lamina densa: 50nm finely granular or filamentous material of type IV collagen The location of principal molecular constituents of junction Epithelial cell LP Ten Cate’s Oral Histology, 2003  Clinical consideration Auto-immune diseases: antibodies directed against any element of the desmosomes, hemidesmosomes, basement membrane. Split between epithelium & underlying connective tissue – sloughing of epithelium Oral Mucosa Composition Main components: Overlying epithelium Basement membrane between epithelium & lamina propria Underlying connective tissue (lamina propria)  Lamina Propria Connective tissue supporting the epithelium Two layers: Papillary LP between rete ridges Reticular (net- like) LP  Lamina Propria Cells Blood vessels Neural elements Fibers embedded in ground substance Image from Oral Anatomy, Histology and Embryology by Berkovitz et al. 2018  Vascular supply of mucosa Deep plexus of vessels in submucosa or deep reticular Lamina layer Propria When submucosa is absent: secondary plexus in LP which (LP) is necessary for all the metabolic needs of the avascular epithelium  Cell types of LP: Fibroblasts Macrophages Mast cells Inflammatory cells Lamina Propria Fibres of LP Collagen (type I & III and IV & VII in basal lamina) Elastic fibres Ground substance  Regional variations in Non-keratinised/ mucosal structure Lining/Alveolar Mucosa: Labial mucosa inside lips Cheek Soft palate Floor of mouth & ventral surface of tongue Keratinised/ masticatory Mucosa: Hard palate Gingiva Image from Oral Anatomy, Histology and Embryology by Berkovitz et al. 2018 Specialised mucosa: Vermillion border of lips Dorsum of tongue  Specialised mucosa of the tongue Functionally masticatory mucosa with additional specialised structures: the taste buds http://anatomy.iupui.edu/courses/histo_D502/D502f04/lecture.f04/upperdigf04/tongue. jpg  Specialised mucosa of the tongue Embryology: Sulcus terminalis divides tongue into: Anterior 2/3: masticatory mucosa with specialised papillae and taste buds Posterior 1/3: lingual tonsils  Tongue papillae Filiform papillae Cover entire anterior 2/3 Hair-like, especially when elongated (Pathology) Core of connective tissue covered by thick keratinised epithelium Abrasive surface that aids in compressing and breaking food against palatal mucosa Image from Oral Anatomy, Histology and Embryology by Berkovitz et al. 2018  Tongue papillae Fungiform Fungus-like/ mushroom- shaped papillae Scattered between filiform papillae anterior tongue Red due to vascularisation Contains taste buds Foliate Sometimes lateral tongue of humans May contain taste buds Image from Oral Anatomy, Histology and Embryology by Berkovitz et al. 2018  Tongue papillae Circumvallate papillae 8-12 papillae adjacent and anterior to sulcus terminalis Large with deep, circular groove surrounding it Do not project above normal surface level Keratinised mucosa overlying Non-keratinised mucosa on lateral borders with taste buds therein Von Ebner serous minor salivary glands open into sulcus Image from Oral Anatomy, Histology and Embryology by Berkovitz et al. 2018  Taste buds Chemoreceptor organs for taste Are modified epithelial cells that transmit to nerve endings and are therefore neuroepithelial cells Do not divide, renewed by differentiation from surrounding epithelium http://medic.med.uth.tmc.edu/inline/inlnimg/00000 670.gif  Taste buds Found in : Mostly in lateral wall of circumvallate papillae Lateral wall of foliate papillae In small numbers upper surface of fungiform papillae Mucosa of soft palate Epiglottis mucosa  Histology of Taste Buds Barrel-shaped clusters of 30-80 spindle-shaped cells orientated at right angles to oral epithelium Different types of cells(Type I-IV) Extends from basal lamina to free surface of epithelium Ends in taste pore Outer ring formed by squamous epithelial cells Inner ring and floor of pore formed by taste bud cells  Taste pore is sealed from oral cavity: these substances absorb to microvilli surface Taste buds Neural innervation: Anterior 2/3 tongue – N VII Posterior 1/3, circumvallate & foliate papillae – NIX Soft palate – Greater petrosal nerve of N VII Pharynx & epiglottis – NX All taste fibers converge in tractus solitarius of brainstem Second order neuron: Thalamus Third order neuron: gustatory center in parietal lobe cortex  Four basic tastes: Ant tongue: sweet and salty Post tongue: bitter Post lateral tongue: sour No differences between taste buds in different taste regions  Lip Has skin on its outer and labial mucosa on its inner surface. Separated by vermilion zone (red zone). Striated muscles in their core Minor mucous salivary glands in the submucosa Skin: dermis and epidermis with flat border in between them Connective tissue: sweat glands, sebaceous glands and bases of hair follicle.  Vermilion zone Lacks appendages of skin Sebaceous glands at the angles of mouth Lacks mucous glands, needs constant moistening with saliva. Keratinised translucent epithelium Long and narrow connective tissue papillae with capillary loops. Junction between vermillion zone and labial mucosa is INTERMEDIATE ZONE – no granular layer, thick Parakeratinised layer. Intermediate zone forms suckling pads in infants Turnover times of oral epithelium (time necessary to replace all the cells in the epithelium) The time taken for a cell to divide and pass through the entire epithelium. Skin 52-75 days Gingiva 41-57 days Cheek 25 days (non-keratinised epithelium turns over faster than keratinised epithelium) Junctional epithelium 5-6 days  Age changes of oral mucosa Mucosal surface is smoother, dryer, atrophic and friable due to cumulative effect of systemic diseases and medication. Histologically: epithelium is thinner, smooth epithelium-connective tissue interface, flattening of epithelial ridges, lamina propria shows decreased cellularity and increased amount of cross-linked collagen. Dorsum of the tongue: glossy appearance, reduced number of filiform papillae, more prominent fungiform papillae Declined cell-mediated immunity Development of varicosities Sebaceous glands of the lips and cheeks are more prominent, minor salivary glands show atrophic signs. Dryness of mouth, burning sensation, abnormal taste Cropped image from Ten Cate’s Oral Histology, 2016