OP 06 - Oral Mucosa and Mucosal Sensation

Oral cavity

The oral cavity is the region that begins where the oral mucosa is present.

Anterior boundary of the oral cavity

The junction of the dry vermillion border and moist labial mucosa.

Posterior boundary of the oral cavity

The palatoglossal folds.

Lateral boundary of the oral cavity

The buccal mucosa.

Superior boundary of the oral cavity

The hard and soft palate.

Inferior boundary of the oral cavity

The floor of the mouth.

Skin of the lip

The skin forms part of the “dry” lip and contains dermal appendages.

Dry lip

The external portion of the lip covered by skin and containing dermal appendages.

Vermillion border

A sharp demarcation between the dry lip and moist labial mucosa characterized by a distinct and uniform coloration.

Labial mucosa

The moist inner surface of the lip characterized by prominent vascularity and the presence of minor salivary glands.

Characteristics of labial mucosa

• Prominent vascularity.

• Contains minor salivary glands.

Palatoglossal folds

The anterior folds that form the posterior boundary of the oral cavity.

Palatopharyngeal fold

The posterior fold located behind the palatoglossal fold.

Tonsillar fauces

The region containing the palatine tonsils, which are composed of lymphoid tissues.

Palatine tonsils

Lymphoid tissues located within the tonsillar fauces involved in immune defense.

Oral mucosa

The mucous membrane lining the oral cavity composed of three major components: epithelium, basal lamina, and lamina propria.

Three major components of oral mucosa

1. Epithelium.

2. Basal lamina.

3. Lamina propria.

Protection function of oral mucosa

The oral mucosa protects underlying tissues from mechanical forces, pathogens, and environmental exposure.

Sensation function of oral mucosa

The oral mucosa contains sensory receptors responsible for detecting stimuli such as pain, temperature, pressure, touch, and texture.

Secretion function of oral mucosa

The oral mucosa contributes to secretion through associated minor salivary glands and mucosal secretions.

Oral epithelium

The epithelial component of the oral mucosa composed of stratified squamous epithelium.

Type of epithelium found in oral mucosa

Stratified squamous epithelium.

Origin of oral epithelium

Oral epithelium is ectodermal in origin.

Main epithelial cells of oral epithelium

Keratinocytes.

Keratinocytes

The major epithelial cells responsible for producing keratin and forming the protective epithelial layer.

Vascularity of oral epithelium

Oral epithelium is avascular; nutrients are supplied by diffusion from the underlying connective tissue.

Non-keratinocytes

Specialized epithelial cells that are not primarily involved in keratin production.

Types of non-keratinocytes in oral epithelium

1. Langerhans cells.

2. Melanocytes.

3. Merkel cells.

Langerhans cells

Immune-related non-keratinocytes located mainly in the stratum spinosum that function as antigen-presenting cells.

Location of Langerhans cells

Stratum spinosum.

Function of Langerhans cells

Antigen presentation and immune surveillance.

Melanocytes

Pigment-producing non-keratinocytes located in the stratum basale.

Location of melanocytes

Stratum basale.

Function of melanocytes

Production of melanin pigment.

Merkel cells

Specialized sensory epithelial cells involved in mechanoreception.

Function of Merkel cells

Detection of mechanical stimuli such as pressure and touch.

Keratinized epithelium

Oral epithelium containing large cytokeratin fibrils and a superficial stratum corneum composed of flattened cells lacking nuclei and organelles.

Non-keratinized epithelium

Oral epithelium containing smaller cytokeratin filaments with a superficial stratum superficiale where cells retain nuclei and organelles.

Cytokeratin in keratinized epithelium

Contains larger cytokeratin fibrils.

Cytokeratin in non-keratinized epithelium

Contains smaller cytokeratin filaments.

Surface layer of keratinized epithelium

Stratum corneum.

Surface layer of non-keratinized epithelium

Stratum superficiale.

Cells of the outer layer of keratinized epithelium

Flattened cells without nuclei and organelles due to complete keratinization.

Cells of the outer layer of non-keratinized epithelium

Cells retain nuclei and organelles.

Resistance of keratinized epithelium to desiccation

Keratinized epithelium is relatively impermeable and prevents dehydration because of its keratinized surface layer.

Resistance of non-keratinized epithelium to desiccation

Non-keratinized epithelium is permeable and remains moist.

Resistance to compression of keratinized epithelium

Keratinized epithelium is more resistant to compression.

Resistance to compression of non-keratinized epithelium

Non-keratinized epithelium is less resistant to compression.

Layers of keratinized epithelium (superficial to deep)

1. Stratum corneum.

2. Stratum granulosum.

3. Stratum spinosum.

4. Stratum basale.

Stratum corneum

The outermost layer of keratinized epithelium composed of flattened, dehydrated cells that have lost their organelles.

Main feature of stratum corneum

Flattened cells with loss of nuclei and organelles due to keratinization.

Stratum granulosum

The layer containing keratohyaline granules within the cytoplasm.

Keratohyaline granules

Cytoplasmic granules involved in keratin formation found in the stratum granulosum.

Stratum spinosum

The epithelial layer where cells increase in size and become more elliptical or oval.

Main characteristic of stratum spinosum

Enlarged oval-shaped cells involved in keratinocyte maturation.

Stratum basale

The deepest layer of keratinized epithelium composed of a single layer of cuboidal or columnar cells.

Function of stratum basale

It is the highly mitotic layer responsible for generating new epithelial cells.

Layers of non-keratinized epithelium

1. Stratum superficiale.

2. Stratum intermedium.

3. Stratum spinosum.

4. Stratum basale.

Stratum superficiale of non-keratinized epithelium

The superficial layer containing slightly flattened cells that retain nuclei and some organelles.

Stratum intermedium

The layer containing slightly flattened cells with dispersed tonofilaments.

Tonofilaments

Intermediate filament structures involved in maintaining epithelial cell structure.

Stratum spinosum of non-keratinized epithelium

The layer composed of more ovoid cells.

Stratum basale of non-keratinized epithelium

The innermost single layer of cuboidal or columnar cells that is highly mitotic.

Basal lamina

A specialized extracellular matrix interface that connects the oral epithelium to the underlying connective tissue (lamina propria).

Function of basal lamina

Provides attachment between the epithelium and connective tissue while maintaining structural support and separation between the two tissues.

Location of basal lamina

Found between the oral epithelium and the underlying lamina propria.

Two components of basal lamina

1. Lamina lucida.

2. Lamina densa.

Lamina lucida

The superficial layer of the basal lamina that is attached to basal epithelial cells through hemidesmosomes.

Attachment of lamina lucida to epithelial cells

Through hemidesmosomes located on basal epithelial cells.

Hemidesmosomes

Specialized attachment structures that anchor basal epithelial cells to the basal lamina.

Function of hemidesmosomes

Secure attachment of epithelial cells to the underlying basal lamina.

Lamina densa

The deeper layer of the basal lamina containing anchoring fibrils responsible for attaching collagen fibers of the underlying lamina propria.

Function of anchoring fibrils

Attach the basal lamina to collagen fibers within the lamina propria, providing stability.

Basal lamina disorders

Diseases involving disruption or immune-mediated damage to the basal lamina zone, resulting in epithelial separation and blister formation.

Autoimmune blistering disease involving basal lamina

A disorder where antibodies target components of the basal lamina zone, causing separation between epithelial layers and connective tissue.

Clinical manifestations of basal lamina disorders

1. Intraoral erosive or ulcerative lesions.

2. Cutaneous bullae or blisters.

Immunofluorescence findings in basal lamina disorders

Linear staining along the basement membrane zone, confirming involvement of the basal lamina.

Lamina propria

The connective tissue layer that supports the oral epithelium.

Main function of lamina propria

Provides structural support, nourishment, vascular supply, and sensory innervation to the epithelium.

Composition of lamina propria

Primarily composed of type I and type III collagen fibers.

Vascularity of lamina propria

Lamina propria is vascular and contains blood vessels that supply nutrients to the avascular epithelium.

Nerve supply of lamina propria

Contains nerve endings responsible for sensory perception in the oral mucosa.

Rete pegs

Extensions of the epithelium that project downward and overlap with the lamina propria.

Function of rete pegs

Increase the surface area of contact between epithelium and connective tissue, improving attachment and mechanical stability.

Connective tissue papilla

Extensions of connective tissue that project upward and overlap with the epithelium.

Function of connective tissue papilla

Increase epithelial-connective tissue interaction and support.

Two layers of lamina propria

1. Papillary layer.

2. Reticular layer.

Papillary layer of lamina propria

The superficial layer located adjacent to the epithelium.

Location of papillary layer

Upper portion of lamina propria directly beneath the epithelium.

Reticular layer of lamina propria

The deeper layer of lamina propria.

Location of reticular layer

Deeper connective tissue portion beneath the papillary layer.

Major cells found in lamina propria

1. Fibroblasts.

2. Macrophages.

3. Mast cells.

4. Polymorphonuclear leukocytes (PMNs/neutrophils).

5. Lymphocytes.

6. Plasma cells.

Fibroblasts

The principal cells of the lamina propria responsible for secretion of fibers and ground substance.

Main function of fibroblasts

Produce collagen fibers. Produce extracellular matrix ground substance. Maintain connective tissue structure.

Macrophages

Immune cells in the lamina propria responsible for antigen presentation and phagocytosis.

Functions of macrophages

1. Antigen presentation.

2. Phagocytosis of foreign materials and cellular debris.

Histiocyte

A precursor form of macrophages found in connective tissues.

Macrophages in chronic inflammation

Macrophages become more predominant during chronic inflammatory conditions.

Mast cells

Immune cells in the lamina propria responsible for histamine production.

Function of histamine produced by mast cells

Mediates inflammatory and immune responses.