Oral Mucosa

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Oral Mucosa. Dr. Ali Tahir. Mucous membrane. Moist lining of GIT, Nasal passages & body cavities that communicate with the exterior The mucous membrane of oral cavity is called “Oral Mucosa” Located anatomically between skin & GIT mucosa & shows some properties of both
Oral MucosaDr. Ali TahirMucous membraneMoist lining of GIT, Nasal passages & body cavities that communicate with the exteriorThe mucous membrane of oral cavity is called “Oral Mucosa”Located anatomically between skin & GIT mucosa & shows some properties of bothBecause of its various functions, it is considered an organDr. Ali Tahir, M.Phil (Part I)Functions of Oral Mucosa
  • Protection
  • From mechanical forces & abrasion while chewing food & from micro-organisms resident in the oral cavity
  • Sensation
  • Temperature, Touch, Pain, Taste
  • Receptors for Satisfaction of thirst, Swallowing, gagging, salivation
  • Secretion
  • Major secretion is saliva
  • Major & minor salivary glands
  • Sebaceous glands are frequently present (upper lip & buccal mucosa) sometimes called Fordyce’s spots but their secretions are insignificant
  • May be an accident of embryologic development
  • Dr. Ali Tahir, M.Phil (Part I)AnatomyTwo parts
  • Outer vestibule (bounded by lips & cheeks)
  • Oral cavity proper (separated from vestibule by teeth & gingiva)
  • Superiorly bound by hard & soft palate
  • Inferiorly by floor of mouth & tongue
  • Posteriorly by pillars of fauces
  • Dr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)Types
  • Lining Mucosa
  • Constitutes the large part (60%)
  • Soft, pliable
  • Masticatory mucosa
  • 25%
  • Firm, immobile
  • Gingiva & hard palate
  • Specialized mucosa
  • Dorsum of tongue, in the form of papillae
  • Unique to oral cavity
  • 15%
  • Dr. Ali Tahir, M.Phil (Part I)Clinical features
  • Oral mucosa is more deeply coloured compared to skin
  • B/c of
  • Concentrated & dilated blood vessels
  • Thickness of epithelium
  • Degree of keratinization
  • Amount of melanin
  • Inflamed mucosa is more red b/c of dilation of blood vessels
  • Dr. Ali Tahir, M.Phil (Part I)Components
  • Two main components
  • Stratified Squamous Epithelium (oral Epithelium)
  • Lamina Propria
  • Interface b/w these two is irregular consisting of C.T papillae & rete ridges/pegs
  • Basal lamina separates the two
  • Dr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)Types & Layers of EpitheliumKeratinized EpitheliumHard palate gingiva & tongue
  • Basal cell layer
  • Prickle cell layer
  • Granular cell layer
  • Keratinized layer
  • Non-keratinized EpitheliumBuccal mucosa, floor of mouth, ventral surface of tongue
  • Basal cell layer
  • Prickle cell layer
  • Intermediate cell layer
  • Superficial cell layer
  • Dr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)SubmucosaA layer of loose fatty or glandular connective tissue may be present between the oral mucosa & underlying bone/muscleThis layer contains blood vessels, nerves & minor salivary glandsComposition of submucosa determines the flexibility of the attachment of oral mucosa to underlying sturucturesEg, in gingiva & hard palate, oral mucosa is directly attached to periosteum & no submucosa is present. This is called mucoperiostium & is firm and inelasticDr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)Lymphoid tissue
  • In several regions, nodules of lymphoid tissue consisting of crypts formed by invaginations of the epithelium into the lamina propria are present
  • Mostly present in posterior parts of oral cavity
  • Lingual tonsils
  • Palatine tonsils
  • Pharyngeal tonsils
  • Together form Waldeyer’s ring
  • Small nodules may also be present in soft palate, ventral surface of tongue & floor of mouth
  • Dr. Ali Tahir, M.Phil (Part I)Oral epithelium
  • Consist of tightly packed cells called keratinocytes
  • Maintains its structural integrity by a continuous process of cell renewal
  • Two types of cell population
  • Progenitor cells
  • Maturing cells
  • Cells produced by mitosis in the deeper layers (basal & parabasal layers) migrate to the surface layers
  • Dr. Ali Tahir, M.Phil (Part I)Epithelial proliferation
  • Dividing cells are present in clusters at the bottom of epithelial ridges
  • Progenitor population consists of two groups
  • Stem cells (slow cell cycle)
  • Produce basal cells & retain proliferative potential of tissue
  • Amplifying cells
  • Increase the no. of cells available for maturation
  • After division, each daughter cell recycles in the progenitor population or enters the maturing population
  • Time required to replace all the cells in the epithelium is called Turnover time
  • Dr. Ali Tahir, M.Phil (Part I)Turn over timeWide range of estimates have been made52-75 days for skin4-14 days for gut41-57 days for gingiva25 days for cheekNon-keratinized epithelium turns over faster than the keratinizedDr. Ali Tahir, M.Phil (Part I)Significance
  • Cancer chemotherapy drugs block the life cycle of cancer cells as well as normal host cells
  • Cells with short turnover time are most affected. These include
  • Blood cells precursors in bone marrow
  • Intestinal epithelium
  • Oral epithelium
  • Leads to formation of oral ulcers
  • In addition, inflammation also affects rate of mitosis
  • Dr. Ali Tahir, M.Phil (Part I)Factors influencing the epithelial proliferationEpidermal growth factorKeratinocyte growth factorInterleukin-1Transforming growth factor α and ßDr. Ali Tahir, M.Phil (Part I)KeratinizationPresent on masticatory mucosa (hard palate, gingiva, parts of dorsal surface of tongue)Inflexible, tough, abrasion resistant, tightly bound to lamina propriaProcess of maturation is called keratinization or cornificationDr. Ali Tahir, M.Phil (Part I)KeratinizationBasal cell layer (stratum basale)Cuboidal or columnar cells containing bundles of tonofibrils. Site of most cell divisionsPrickle cell layer (stratum spinosum)Larger, ovoid cells with conspicoustonofibril bundles, upper part of layer contains membrane-coating granulesGranular cell layer (Stratum granulosum)Flattened cells, keratohyaline granules associated with tonofibrilsKeratinized (stratum corneum)Extremely flattened & dehydrated cells with loss of all organells, cells filled with fibrillar material. If pyknoticnuclie retained, called para-keratinizedDr. Ali Tahir, M.Phil (Part I)Non-keratinizedBasal cell layer (stratum basale)Cuboidal/columnar cells containing separate tonofilamentsPrickle cell layer (stratum spinosum)Larger ovoid cells containing dispersed tonofilaments, membrane coated granules in upper part of layerIntermediate layer (stratum intermedium)Slightly flattened cells containing dispersed tonofilaments & glycogenSuperficial layer (stratum superficiale)Slightly flattened cells, dispersed tonofilaments, glycogen, fewer organelle, nuclieDr. Ali Tahir, M.Phil (Part I)Ultra structure of epithelial cellsCells of basal layer are least differentiated cellsContain organelles & certain structures such as tonofilaments & desmosomesTonofilaments are fibrous proteins & belong to the class of intermediate filamentsAggregate to form bundles called tonofibrilsChemically represent cytokeratins which are chracteristic constituents of epithelial cellsDr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)Keratins
  • Represent a large family of proteins
  • Classified according to the molecular weight & charge. E.g..
  • Low molecular weight (40kDa) found in glandular & simple epithelia
  • Intermediate molecular weight found in stratified epithelia
  • High molecular weight (67kDa) in keratinized stratified epithelia
  • Keratinzed epithelium has
  • Type1, 5, 6, 10, 14, 16
  • Non-keratinized epithelium has
  • Type 4, 5, 13, 14, 19
  • Dr. Ali Tahir, M.Phil (Part I)Adhesions & AttachmentsCohesion b/w cells is provided by protein-carbohydrate complexes produced by epithelial cells themselvesIn addition, modifications of adjacent cell membranes of cells called desmosomes provide attachment into which tonofilaments insertAdherence b/w epith & C.T is provided by hemidesmosomes which attach the cells to basal laminaDr. Ali Tahir, M.Phil (Part I)Adhesions & Attachments
  • Two other types of connections are
  • Gap junctions
  • Tight junctions
  • Gap junction:
  • Membranes of adjacent cells run closely together separated by a small gap
  • Small interconnections are present
  • Gap junctions allow electric/chemical communication
  • Tight junction
  • Adjacent cell membranes are tightly apposed
  • Dr. Ali Tahir, M.Phil (Part I)Membrane-coated granulesAlso called lamellate granulesAre small memrane bound structures about 250nm in size containing glycolipid, originate from golgi complexAppear in the upper part of prickle layerThey are elongated in keratinized & circular in non-keratinized epitheliumIn the upper part of stratum granulosum/intermedium, these granules appear to fuse with superficial cell membrane to discharge their contents into intercellular spaceDr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)Cell Maturation in Keratinized epithCells in the superficial part of granular layer develop a thickening on the intra-cullular aspect of their membraneIt contributes in resistance of keratinized layer to chemical solventsOne of the major constituent of this thickening is a protein called involucrinDr. Ali Tahir, M.Phil (Part I)Granular layerFound in keratinized epitheliumContains keratohyalin granules, which are basophilic granules under light microscopeThese are irregular in shape0.5-1nm in sizeSynthesized by ribosomesIntimately associated with tonofibrilsFacilitate aggregation & formation of cross-links b/w cytokeratin filamentsProteins making bulk of these granules are called LoricrinDr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)SquamesAs the cells of granular layer reach the junction with the keratinized layer, a sudden change occursAll organelles are lost, including nuclie & keratohyalin granulesCells dehydrate & assume the shape of hexagonal disksThese are called squamesSquames are lost within days, a process called desquamation & replaced by cells from underlying layersLimit the colonization of pathogenic micro-organismsKeratin layer in oral cavity may be upto 20 layers of squamesDr. Ali Tahir, M.Phil (Part I)Cell maturation in non-keratinized epitheliumA slight increase in size occurs in intermediate cell layerAccumulation of glycogen in cells of surface layerOccasionally keratohyalin granules are seen but these aren’t associated with tonofilamentsThese granules may remain upto the surface layerDr. Ali Tahir, M.Phil (Part I)Non-keratinized epitheliumCells in the superficial layer are slightly more flattenedContain dispersed tonofilaments, retain nuclie & do not dehydrateThus are tolerant to compression & distensionDr. Ali Tahir, M.Phil (Part I)Anatomical variationsSome variation of anatomical locations of keratinized & non-keratinized epithelium may occurHyperkeratosis of keratinized oral epithelium is physiological to chronic irritationHyperkeratosis of non-keratinized epithelium can be associated with abnormal cellular changes that can lead to cancerInflammation of gingiva can lead to loss of keratinization or parakeratinizationThese changes are usually reversible when irritant is removedDr. Ali Tahir, M.Phil (Part I)Permeability & absorption of oral epitheliumOral epithelium is largely impermeable & lacks absorptive capacityEpithelium at the floor of the mouth, however, is thin & more permeable comparatively (Nitroglycerin to relieve angina pain)Oral epithelium thus limits the absorption of toxins from micro-organisms except in dentogingival junctionDr. Ali Tahir, M.Phil (Part I)Other cells in oral epithelium
  • Melanocytes
  • Present in basal layer
  • Lack desmosomes & tonofilaments
  • Dendritic, synthesis of melanin pigment granules (melanosomes)
  • Merkel Cells
  • Present in basal layer
  • Non-dendritic, tactile sensation
  • Langerhans cells
  • Dendritic
  • Present in parabasal layer
  • Antigen trapping & processing
  • Lymphocytes
  • Variable location
  • Inflammatory response
  • B or T cells
  • Dr. Ali Tahir, M.Phil (Part I)Pigmentation
  • Two types of pigmentation is seen in oral mucosa
  • Endogenous
  • Exogenous
  • Endogenous pigments in oral mucosa are melanin & hemoglobin
  • Melanocytes are derived from neural crest ectoderm
  • Enter the epithelium at 11th week of gestation
  • Melanosomes are injected into adjacent keratinocytes by long dendritic processes that often pass through several layers of epithelium
  • Groups of melanosomes can be seen under light microscope, called melanin granules
  • Dr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)PigmentationLight & dark individuals have the same number of melanocytes, the difference results from the activity of melanocytesIn persons with heavy melanin pigmentaion, melanophages are seen in the connective tissueIn oral mucosa, melanin pigmentation is most commonly seen in gingiva, buccal mucosa, hard palate & tongue & is more in dark skinned individualsDr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)Pigmented pathologies
  • Oral melanoticmacule
  • Increased production of melanin pigment without proliferation of melanocytes
  • Nevus (Mole)
  • Benign proliferation of melanocytes
  • Melanoma
  • Malignant tumour of melanocytes
  • Melanoma of oral cavity is aggressive
  • Dr. Ali Tahir, M.Phil (Part I)Pigmentation
  • Exogenous
  • Caused by foreign material introduced locally or systemically
  • One of the most common oral exogenous pigment is amalgum
  • Gives rise to bluish-gray patch called amalgum tattoo
  • Systemic administration of metals such as lead & bismuth can cause gingival margin pigmentation (called Burton’s line)
  • Dr. Ali Tahir, M.Phil (Part I)MCQsStratum distendumis another name forSubmucosa of lining oral epitheliumPrickle layer of non-keratinized epitheliumSuperficial layer of Non-keratinized epitheliumGranular layer of keratinized epitheliumDr. Ali Tahir, M.Phil (Part I)MCQsThe superficial cells of granular layer of keratinized oral epithelium have intra-cellular thickenings to resist chemical solvents containing which proteins?CytokeratinsGlycoproteinsInvolucrinFilaggrinDr. Ali Tahir, M.Phil (Part I)MCQsBlood flow in oral mucosa is the greatest in which regionSoft palateFloor of mouthGingivatongueDr. Ali Tahir, M.Phil (Part I)MCQsIn infants, Suckling Pad refers toA thickened vermillion zoneA thickened intermediate zone A thickened labial mucosaA thickened muco-cutaneous junctionDr. Ali Tahir, M.Phil (Part I)MCQsDr. Ali Tahir, M.Phil (Part I)Dr. Ali Tahir, M.Phil (Part I)
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