Oral Mucosa - Comprehensive Notes
# Oral Mucosa ## Learning Objectives * Identify the anatomical features of the oral cavity, including the vestibule and oral cavity proper. * Describe the variable distribution of lining mucosa and masticatory mucosal surfaces in the oral cavity and the functional reasons for these differences. * Identify and describe the microscopic (LM) structure of the different regions of the lips, including the structure and functional differences between skin, transitional, vermilion, and labial zones. * Demonstrate understanding of the functional reasons for the regional variation of the masticatory and lining mucosa epithelium-connective tissue interface structure. * Describe the structure and functions of the specialized mucosa of the tongue, including the epithelium and different types of lingual papillae. * Understand the structure and function of tastebuds and their supporting tissues. * Explain how and why the lining mucosa of the mouth floor can play a special role in medical treatments or therapies. ## Mucosa Types and Locations ### Lining Mucosa * Non-keratinized stratified squamous epithelium. * Locations: * Lips. * Buccal mucosa. * Alveolar mucosa. * Soft palate. * Underside of the tongue. * Floor of the mouth. ### Masticatory Mucosa * Keratinized stratified squamous epithelium. * Locations: * Hard palate. * Attached gingiva. * Dorsum of tongue. * Areas exposed to mechanical abrasion, physical, thermal, or chemical damage. * Exhibits distinct resistance to deformation under load. ### Specialized Mucosa * Dorsal surface of the tongue, featuring different types of papillae, some bearing taste buds. ## Lip Zones * **Vermilion Zone:** * Thin, orthokeratinized stratified squamous epithelium. * Numerous narrow papillae; capillary loops close to the surface in papillary layer. * Mucosa firmly attached to underlying muscle * Some sebaceous glands in vermilion border, minor salivary glands and fat in intermediate zone. * **Intermediate Zone:** * Thin, parakeratinized stratified squamous epithelium. * **Masticatory Mucosa**: Gingival and Hard Palate * **Gingival:** Thick (\)approx 250\mu m), orthokeratinized or parakeratinized, stratified squamous epithelium often showing stippled surface. * Long irregular papillae; elastic and collagen fibers in connective tissue. * No distinct layer, mucosa firmly attached by collagen fibers to cementum and periosteum of alveolar process ("mucoperiosteum"). * **Hard Palate:** Thick, orthokeratinized (parakeratinized, in parts), stratified squamous epithelium thrown into transverse palatine ridges (rugae). * Long, narrow papillae, dense collagenous connective tissue; long capillary loops with numerous anastomoses. * Dense collagenous connective tissue attaching mucosa to periosteum ("mucoperiosteum"), fat, and minor salivary glands are packed into connective tissue in regions where mucosa overlies lateral palatine neurovascular bundles. * **Specialized Mucosa**: Dorsal Surface of Tongue * Thick, keratinized, and non-keratinized, stratified squamous epithelium forming three types of papillae, some bearing taste buds. * Long papillae; minor salivary glands in posterior portion; rich innervation, particularly near taste buds; capillary plexus in papillary layer, large vessels lying deeper. * No distinct layer; mucosa is bound to connective tissue surrounding musculature of tongue. ## Lip Appearance - Transition Zone * Oral mucosa is continuous with the skin yet appearance differs particularly at lips. * Lip coloration is influenced by: * Capillary concentration. * Capillary dilation. * Epithelium thickness. * Melanin pigment present. * Thinly keratinised. * Protein eleidin (transparent protein found in Stratum Lucidum). * Note: eleidin is converted to keratin in stratum corneum of skin ## Lip Anatomy * Regions: * Vermilion border. * Labial mucosa. * Thin skin. * Structures: * Skin of the lip. * Vermilion border. * Labial mucosa. * Orbicularis oris muscle. * Hair. * Sebaceous gland. * Labial salivary glands. * Minor salivary glands. * Capillaries. * Neurovascular bundle. * Pilosebaceous units. * Skeletal muscle. * Adipose tissue. ## Gingiva and Alveolar Mucosa * Regions: * Attached gingiva. * Interdental gingiva. * Marginal gingiva. * Alveolar mucosa. * Structures: * Maxillary labial frenum. * Maxillary vestibule. * Crown. * Mandibular buccal frenum. * Gingival margin. * Gingival groove. * Mucogingival junction. * Mandibular vestibule. * Bone. ## Buccal Mucosa * Layers: * Stratum Corneum (Horny Layer). * Stratum Lucidum. * Stratum Granulosum (Granular Layer). * Stratum Spinosum (Squamous Cell Layer). * Stratum Basale (Basal Layer). * Dermal-Epidermal Junction (DEJ). * Papillary Dermis. * Reticular Dermis. ## Masticatory Mucosa - Strength and Resistance * Increase in number and depth of connective tissue papillae in tissues where high level of strength & resistance is required (e.g., masticatory mucosa). ## Oral Mucosa - Hard Palate * Layers: * Epithelium: * Keratinized stratified squamous. * Lamina Propria. * Submucosa. ## Specialised Mucosa - Tongue * Features: * Striated muscle bundles running in 3 planes. * Variable mucosa. * Specialized mucosal features: papillae. * **Papillae Types:** * **Filiform:** Many, rough, keratinised. * **Fungiform:** Less, interspersed, light Keratinisation. * **Foliate:** Few, parallel ridges. * **Circumvallate** ## Tongue Mucosa * **Dorsal Surface:** * Lingual mucosa. * Keratinised stratified squamous epithelium. * Numerous surface specializations: papillae, taste buds, lingual glands. * **Ventral Surface:** * Non-keratinised stratified squamous epithelium. ## Tongue Surface Specializations * Papillae types: circumvallate, foliate, fungiform. * Taste buds located on papillae, containing epithelial cells, outer taste pore, microvilli, nerve synapses, sensory cells, supporting cells, basal cells. ## Types of Papillae * **Filiform Papilla:** * Most numerous, conical with keratinized tips. * No taste buds. * **Fungiform Papilla:** * Mushroom-shaped, highly vascularized connective tissue core. * Taste buds present. * **Circumvallate Papilla:** * Surrounded by a circular trench. * Openings of the ducts of serous glands of Von Ebner. * **Foliate Papilla:** * Not well developed in humans. * **Location:** Anterior 2/3 of tongue, posterior 1/3 with sulcus terminalis. * Vallate papillae, connective tissue tongue epithelium, mucus-secreting gland. ## Specialised Mucosa - Tongue Vallate (Circumvallate) Papillae * Largest papillae. * Contain salivary ducts with serous secretion. * Continuous flow. * Secrete Lipase and gustin. * Lateral surface is non-keratinized and contain >200 taste buds. ## Fungiform & Filiform Papillae * Taste buds exist on fungiform papillae but not filiform papillae. ## Taste Buds * Not present in keratinised filiform papillae * Widely scattered on tongue. * Dorsal & lateral surface. * Contain 50-100 cells each. * Found on Fungiform & circumvallate papillae ## Taste Bud Structure * Neurosensory epithelial structures embedded in the surface epithelium of fungiform and circumvallate papilla. * Appear as onion-like, oval, pale staining structures. * Extend through the full thickness of epithelium. * Open on the surface through taste pore. * Types: Receptor cells, supporting cells and basal cells. * Contain microvilli. * Found within stratified squamous epithelium. * Located above a trench in the connective tissue. ## Taste Bud Function * Chemoreceptors. * About 10,000 in oral cavity, uvula, epiglottis & throat. * Most on dorsum of tongue. * Chemical tastants dissolved in saliva. * Receptors bind selectively to tastant in solution. * Receptor cells are modified epithelial cells with microvilli that protrude through taste pore, increasing plasma membrane surface area. * Receptor sites on plasma membrane stimulate depolarising action potential. * Promotes neurotransmitter release. ## Comparison with Skin * The dry covering. * Exterior covering of body. * Continuous with oral cavity at lips. * Oral mucosa resembles skin in some respects. ## Oral Mucosa Appearance vs. Skin * Deeper color. * Moist surface. * Smooth surface (exceptions: tongue papillae, hard palate rugae, gingival stippling). * Absence of appendages. * Sebaceous gland limited distribution in oral tissues; not associated with hair follicles. * Mucosal extra cellular matrix (ECM) resembles fetal skin. * Lower inflammatory response. ## Skin and Mucosa - Basic Structure * All have covering epithelia and underlying connective tissue. * Form follows function. ## Skin vs. Oral Mucosa Layers
Skin | Oral Mucosa |
|---|---|
Epidermis | Oral epithelium |
Basal lamina | Basal lamina |
Dermis | Lamina propria |
Subcutaneous tissue | Submucosa/Bone |
* Cell types: Mast cell, Macrophage, Fibroblast, Keratinocyte, Nerve ending, Langerhands cell. * Other components: Bone, Blood Vessel ## Skin & Oral Mucosa Functions * **Similarities:** * Protection. * Sensory perception. * Synthesis. * Secretion (mucosal layers). * Thermal regulation. * Aesthetics. ## Wound Healing * Similar stages of repair & healing in skin & oral mucosa wound healing is a multi-step process. * Epithelial cells in the immediate vicinity of the wound edges undergo wound re-epithelialisation through proliferative and migratory burst, replacing keratinocytes lost. * Keratinocyte function is critical. * **SKIN:** Scar formation usually results; ranges from minor (no impact on physiologic function) to hypertrophic scarring and contractures (impact on physiologic function). ## Oral Mucosa Wound Healing - Differences * Both skin & mucosa proceed through similar stages, but there are differences. * Oral mucosa healing is rapid (4x speed of epithelial skin repair) with relatively minimal to no scar formation. * **Reasons for differences:** * Gene expression profiles of oral and skin epithelium are quite different. * Oral wounds exhibit differential expression of specific proliferation and migration associated genes, with epithelial cell migration speed at 2.6x that of skin. * Lower inflammatory response, less immune cell infiltration & different cytokine levels. * Reduced cytokine types that promote scar development. * Fibroblasts in higher proliferative capacity and contractility profile. * Lower Vascular Endothelial Growth Factor; angiogenesis in oral wounds is less than in skin.
Identify the anatomical features of the oral cavity, including the vestibule and oral cavity proper.
Describe the variable distribution of lining mucosa and masticatory mucosal surfaces in the oral cavity and the functional reasons for these differences.
Identify and describe the microscopic (LM) structure of the different regions of the lips, including the structure and functional differences between skin, transitional, vermilion, and labial zones.
Demonstrate understanding of the functional reasons for the regional variation of the masticatory and lining mucosa epithelium-connective tissue interface structure.
Describe the structure and functions of the specialized mucosa of the tongue, including the epithelium and different types of lingual papillae.
Understand the structure and function of tastebuds and their supporting tissues.
Explain how and why the lining mucosa of the mouth floor can play a special role in medical treatments or therapies.
Mucosa Types and Locations
Lining Mucosa
Non-keratinized stratified squamous epithelium.
Locations:
Lips.
Buccal mucosa.
Alveolar mucosa.
Soft palate.
Underside of the tongue.
Floor of the mouth.
Masticatory Mucosa
Keratinized stratified squamous epithelium.
Locations:
Hard palate.
Attached gingiva.
Dorsum of tongue.
Areas exposed to mechanical abrasion, physical, thermal, or chemical damage.
Exhibits distinct resistance to deformation under load.
Specialized Mucosa
Dorsal surface of the tongue, featuring different types of papillae, some bearing taste buds.
Lip Zones
Vermilion Zone:
Thin, orthokeratinized stratified squamous epithelium.
Numerous narrow papillae; capillary loops close to the surface in the papillary layer.
Mucosa firmly attached to underlying muscle
Some sebaceous glands in the vermilion border, minor salivary glands, and fat in the intermediate zone.
Intermediate Zone:
Thin, parakeratinized stratified squamous epithelium.
Masticatory Mucosa: Gingival and Hard Palate
Gingival:
Thick (\approx 250\mu m), orthokeratinized (no nuclei) or parakeratinized (some nuclei), stratified squamous epithelium often showing a stippled surface.
Long irregular papillae; elastic and collagen fibers in connective tissue.
No distinct layer, mucosa firmly attached by collagen fibers to cementum and periosteum of alveolar process ("mucoperiosteum").
Hard Palate:
Thick, orthokeratinized (parakeratinized, in parts), stratified squamous epithelium thrown into transverse palatine ridges (rugae).
Long, narrow papillae, dense collagenous connective tissue; long capillary loops with numerous anastomoses.
Dense collagenous connective tissue attaching mucosa to periosteum ("mucoperiosteum"), fat, and minor salivary glands are packed into connective tissue in regions where mucosa overlies lateral palatine neurovascular bundles.
Specialized Mucosa: Dorsal Surface of Tongue
Thick, keratinized, and non-keratinized, stratified squamous epithelium forming three types of papillae, some bearing taste buds.
Long papillae; minor salivary glands in the posterior portion; rich innervation, particularly near taste buds; a capillary plexus in the papillary layer; large vessels lying deeper.
No distinct layer; mucosa is bound to connective tissue surrounding the musculature of the tongue.
Lip Appearance - Transition Zone
Oral mucosa is continuous with the skin yet appearance differs particularly at the lips.
Lip coloration is influenced by:
Capillary concentration.
Capillary dilation.
Epithelium thickness.
Melanin pigment is present.
Thinly keratinized.
Protein eleidin (transparent protein found in Stratum Lucidum).
Note: eleidin is converted to keratin in the stratum corneum of the skin
Lip Anatomy
Regions:
Vermilion border.
Labial mucosa.
Thin skin.
Structures:
Skin of the lip.
Vermilion border.
Labial mucosa.
Orbicularis oris muscle.
Hair.
Sebaceous gland.
Labial salivary glands.
Minor salivary glands.
Capillaries.
Neurovascular bundle.
Pilosebaceous units.
Skeletal muscle.
Adipose tissue.
Gingiva and Alveolar Mucosa
Regions:
Attached gingiva.
Interdental gingiva.
Marginal gingiva.
Alveolar mucosa.
Structures:
Maxillary labial frenum.
Maxillary vestibule.
Crown.
Mandibular buccal frenum.
Gingival margin.
Gingival groove.
Mucogingival junction.
Mandibular vestibule.
Bone.
Buccal Mucosa
Layers:
Stratum Corneum (Horny Layer).
Stratum Lucidum.
Stratum Granulosum (Granular Layer).
Stratum Spinosum (Squamous Cell Layer).
Stratum Basale (Basal Layer).
Dermal-Epidermal Junction (DEJ).
Papillary Dermis.
Reticular Dermis.
Masticatory Mucosa - Strength and Resistance
The increase in the number and depth of connective tissue papillae in tissues where a high level of strength & resistance is required (e.g., masticatory mucosa).
Oral Mucosa - Hard Palate
Layers:
Epithelium:
Keratinized stratified squamous.
Lamina Propria.
Submucosa.
Specialised Mucosa - Tongue
Features:
Striated muscle bundles running in 3 planes.
Variable mucosa.
Specialized mucosal features: papillae.
Papillae Types:
Filiform:
Many, rough, keratinized.
Fungiform:
Less, interspersed, light Keratinization.
Foliate:
Few, parallel ridges.
Circumvallate: Large, dome-shaped structures located at the back of the tongue, surrounded by a trench, and containing taste buds.
Tongue Mucosa
Dorsal Surface:
Lingual mucosa.
Keratinized stratified squamous epithelium.
Numerous surface specializations: papillae, taste buds, and lingual glands.
Ventral Surface:
Non-keratinized stratified squamous epithelium.
Tongue Surface Specializations
Papillae types: circumvallate, foliate, and fungiform.
Taste buds are located on papillae, containing epithelial cells, an outer taste pore, microvilli, nerve synapses, sensory cells, supporting cells, and basal cells.
Types of Papillae
Filiform Papilla:
Most numerous, conical with keratinized tips.
No taste buds.
Fungiform Papilla:
Mushroom-shaped, highly vascularized connective tissue core.
Taste buds present.
Circumvallate Papilla:
Surrounded by a circular trench.
Openings of the ducts of serous glands of Von Ebner.
Foliate Papilla:
Not well developed in humans.
Location:
Anterior 2/3 of the tongue, posterior 1/3 with sulcus terminalis.
Vallate papillae, connective tissue tongue epithelium, mucus-secreting gland.
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Specialised Mucosa - Tongue Vallate (Circumvallate) Papillae
Largest papillae.
Contain salivary ducts with serous secretion.
Continuous flow.
Secrete Lipase and gustin.
The lateral surface is non-keratinized and contains >200 taste buds.
Fungiform & Filiform Papillae
Taste buds exist on fungiform papillae but not filiform papillae.
Taste Buds
Not present in keratinized filiform papillae
Widely scattered on the tongue.
Dorsal & lateral surface.
Contain 50-100 cells each.
Found on Fungiform & circumvallate papillae
Taste Bud Structure
Neurosensory epithelial structures are embedded in the surface epithelium of fungiform and circumvallate papilla.
Appear as onion-like, oval, pale staining structures.
Extend through the full thickness of the epithelium.
Open on the surface through the taste pore.
Types: Receptor cells, supporting cells, and basal cells.
Contain microvilli.
Found within stratified squamous epithelium.
Located above a trench in the connective tissue.
Taste Bud Function
Chemoreceptors.
About 10,000 in the oral cavity, uvula, epiglottis & throat.
Most on the dorsum of the tongue.
Chemical tastants are dissolved in saliva.
Receptors bind selectively to a tastant in solution.
Receptor cells are modified epithelial cells with microvilli that protrude through the taste pore, increasing plasma membrane surface area.
Receptor sites on the plasma membrane stimulate a depolarizing action potential.
Promotes neurotransmitter release.
Comparison with Skin
The dry covering.
Exterior covering of the body.
Continuous with the oral cavity at the lips.
Oral mucosa resembles skin in some respects.
Oral Mucosa Appearance vs. Skin
Deeper color.
Moist surface.
Smooth surface (exceptions: tongue papillae, hard palate rugae, gingival stippling).
Absence of appendages.
Sebaceous gland limited distribution in oral tissues; not associated with hair follicles.
Mucosal extra cellular matrix (ECM) resembles fetal skin.
Lower inflammatory response.
Skin and Mucosa - Basic Structure
All have covering epithelia and underlying connective tissue.
Form follows function.
Skin vs. Oral Mucosa Layers
Skin | Oral Mucosa |
|---|---|
Epidermis | Oral epithelium |
Basal lamina | Basal lamina |
Dermis | Lamina propria |
Subcutaneous tissue | Submucosa/Bone |
Cell types: Mast cell, Macrophage, Fibroblast, Keratinocyte, Nerve ending, Langerhands cell.
Other components: Bone, Blood Vessel
Skin & Oral Mucosa Functions
Similarities:
Protection.
Sensory perception.
Synthesis.
Secretion (mucosal layers).
Thermal regulation.
Aesthetics.
Wound Healing
Similar stages of repair & healing in the skin & oral mucosa wound healing is a multi-step process.
Epithelial cells in the immediate vicinity of the wound edges undergo wound re-epithelialisation through proliferative and migratory burst, replacing keratinocytes lost.
Keratinocyte function is critical.
SKIN:
Scar formation usually results; ranges from minor (no impact on physiologic function) to hypertrophic scarring and contractures (impact on physiologic function).
Oral Mucosa Wound Healing - Differences
Both skin & mucosa proceed through similar stages, but there are differences.
Oral mucosa healing is rapid (4x speed of epithelial skin repair) with relatively minimal to no scar formation.
Reasons for differences:
Gene expression profiles of oral and skin epithelium are quite different.
Oral wounds exhibit differential expression of specific proliferation and migration-associated genes, with epithelial cell migration speed at 2.6x that of skin.
Lower inflammatory response, less immune cell infiltration & different cytokine levels.
Reduced cytokine types that promote inflammation contribute to the faster healing process observed in oral mucosa compared to skin, facilitating a quicker resolution of injuries.