Oral Mucosa

Mucosa (definition)

Epithelial lining of any opening of the body (GI, respiratory, genitourinary tracts)

Oral mucosa

Wet mucous membrane lining the oral cavity

Most variable layer of the GI tract / location indicator

The epithelial lining

4 layers of the GI tract wall

Mucosa, submucosa, muscularis, serosa and/or adventitia

3 parts of the mucosa (GI)

Epithelium, lamina propria (loose CT with wandering immune cells), muscularis mucosae (smooth muscle, distal GI; not always present)

Submucosa

Dense irregular CT, fairly constant thickness; may contain minor salivary/mucous glands

Muscularis (GI wall)

Muscular layer: smooth or skeletal depending on location

Serosa vs adventitia

Serosa = peritoneum/pleura covering; adventitia = CT where organ is attached (e.g., esophagus on posterior thoracic wall)

Oral vestibule

Space between teeth/gingivae and lips

Oral cavity proper

Space behind the teeth for mastication and lingual manipulation

Fauces (posterior boundary of oral cavity)

Soft palate, glossal arches and palatine tonsils, base of tongue; beyond is the oropharynx

Functions of the oral cavity

Digestion, secretion, taste, protection, absorption, respiration and speech

Digestive function of the oral cavity

Mastication (mechanical) + salivary amylase (starts sugar digestion)

Protective function of the oral mucosa

Stratified epithelium protects vessels/nerves from hot, rough, spicy food; IgA from salivary acinar (serous) cells

Mucosal antibody secreted in saliva

IgA (from salivary acinar cells, especially serous)

Why can medications be absorbed sublingually?

Floor of the mouth has very thin mucosa over a capillary bed

3 types of oral mucosa by location

Lining (60%), masticatory (25%), specialized (15%)

Lining mucosa: epithelium

Non-keratinized stratified squamous (SSE)

Lining mucosa: locations

Buccal, labial, alveolar mucosa; ventral tongue; floor of mouth; soft palate

Masticatory mucosa: epithelium

Parakeratinized (PKSSE) or keratinized (KSSE) stratified squamous

Masticatory mucosa: locations

Attached gingiva, hard palate, dorsum of tongue

Specialized mucosa: epithelium and location

PKSSE to KSSE with papillae; dorsal and lateral surfaces of the tongue

Percent of oral mucosa: lining / masticatory / specialized

60% / 25% / 15%

What determines the degree of keratinization in oral mucosa?

Friction/abrasion — more abrasion = more keratinization

Para- vs fully keratinized masticatory mucosa: is there a rule by location?

No — varies between people (diet); classify by histologic criteria on the image

Most of the oral cavity is lined by…

Non-keratinized stratified squamous epithelium

Lamina propria of oral mucosa

Looser dense irregular CT with small-diameter collagen fibers

Non-keratinized SSE: how to identify

Nuclei present all the way to the surface; cells get smaller toward surface; no keratohyalin granules

Parakeratinized SSE: how to identify

Pyknotic (condensed) nuclei at the apical surface; few keratohyalin granules

Keratinized SSE: how to identify

Apical cells LACK nuclei (dead keratinocytes); considerable keratohyalin granules in stratum granulosum

Hallmark of keratinized epithelium

No nuclei in the apical cells

Keratohyalin granules

Complex with keratin intermediate filaments to fill the cell with keratin; found in stratum granulosum

Desquamation

Shedding of surface cells; epithelium is avascular so cells far from blood supply die

Pyknotic nucleus

Highly condensed nucleus (seen apically in parakeratinized epithelium)

Keratinocytes

Make up most of the epithelium; keratinization adds protection from abrasion

Dermal papillae and epidermal ridges

Interdigitation that protects from shearing and increases attachment surface area

Merkel (tactile epithelial) cells

Basal layer; light touch sensation

Melanocytes

Basal layer; pass melanin to surrounding cells via finger-like projections (don't hold pigment themselves)

Langerhans cells

Immune defense; detect pathogens breaching the barrier (need special stain)

Skin features shared with oral epithelium

Keratinocytes, keratinization, papillae/ridges, Merkel cells, melanocytes, Langerhans cells

ET–CT junction in high-friction areas

Interdigitated: deep epithelial ridges (ER) + connective tissue ridges (CTR); dense irregular CT with larger collagen fibers (e.g., gingiva)

ET–CT junction in low-stress areas

Smooth interface, fewer ridges (e.g., cheek)

3 regions of the lip

External skin, vermilion zone, inner (oral) mucosa

Lip external skin

Keratinized SSE; hair follicles, sweat and sebaceous glands

Sebaceous gland mode of secretion

Holocrine

Lip vermilion zone

Thin KSSE (or parakeratinized); no hair or glands; many superficial blood vessels

Why is the vermilion red/pink?

Thin epithelium over many superficial blood vessels in the lamina propria

Lip inner (oral) mucosa

Non-keratinized SSE (thicker); labial salivary glands (minor, mucous) in submucosa

Labial salivary glands

Minor mucous salivary glands in the lip submucosa (pale cytoplasm, basal nuclei)

Muscle at the core of the lip

Orbicularis oris (skeletal)

Cheek (buccal mucosa) layers

Non-keratinized SSE; lamina propria with short ridges; buccal (mucous) salivary glands; buccinator; thin skin

Muscle of the cheek

Buccinator (skeletal)

Alveolar mucosa

Thin, non-keratinized, red; extends from gingiva to labial/buccal mucosa

Mucogingival junction

Transition between alveolar mucosa (red, non-keratinized) and gingiva (pale, keratinized)

Why is gingiva pale while alveolar mucosa is red?

Gingiva's thick keratinized epithelium hides vessels; alveolar mucosa is thin and non-keratinized

Masticatory mucosa features

PKSSE to KSSE; frequent elongated epithelial and CT ridges; larger collagen fibers; dense irregular submucosa

Mucoperiosteum

CT fused directly with periosteum (no distinct submucosa) → mucosa firmly fixed; hard palate and gingiva

Where is mucoperiosteum found?

Gingiva and hard palate (midline raphe)

Parts of the gingiva relative to the tooth

Attached (to alveolar process), free, marginal (gingival margin); gingival sulcus between tooth and free gingiva

Gingival sulcus

Space between the tooth and the free gingiva

Hard palate anterior submucosa contains…

Adipose tissue

Hard palate posterior submucosa contains…

Palatine mucous salivary glands

Midline raphe of hard palate

Mucoperiosteum — firmly attached

Soft palate: oral vs nasal surface epithelium

Oral: non-keratinized SSE (lining mucosa). Nasal: respiratory epithelium (pseudostratified ciliated columnar with goblet cells)

Lingual papillae of the anterior 2/3

Filiform, fungiform, circumvallate, foliate

Sulcus terminalis

Separates anterior 2/3 from posterior 1/3 of the tongue

Posterior 1/3 of the tongue

No papillae; contains lingual tonsils (lymphoid tissue)

Intrinsic muscles of the tongue

Skeletal muscle in many directions (cross, longitudinal, oblique)

Which papillae LACK taste buds?

Filiform

Filiform papillae

Cone-shaped ('shark fin'), PKSSE–KSSE; most numerous; texture for food manipulation; NO taste buds

Most numerous lingual papillae

Filiform

Fungiform papillae

Mushroom-shaped; mostly near tip; highly vascular CT core; taste buds on the dorsal (top) surface

Circumvallate papillae

8–12 large papillae in a 'V' anterior to sulcus terminalis; deep clefts; taste buds on lateral walls

Glands draining into circumvallate clefts

Serous lingual salivary glands — wash food over taste buds

Where are taste buds on fungiform vs circumvallate papillae?

Fungiform: top (dorsal) surface. Circumvallate: lateral walls

Taste bud

Sensory organ in the epithelium of fungiform, circumvallate, foliate papillae; taste pore; apical microvilli

3 cell types in a taste bud

Neuroepithelial (sensory), supporting, basal (stem) cells

Neuroepithelial (sensory) cells of taste bud

Synapse on afferent nerve fibers to the brain

Supporting cells of taste bud

Like neuroglia; keep sensory cells healthy

Basal cells of taste bud

Stem cells; taste bud regenerates in about 10 days

How fast do taste buds regenerate?

About 10 days

Recurrent aphthous stomatitis (RAS)

'Canker sore'; most common ulcerative oral disorder; unknown etiology, often trauma; minor, major, herpetiform types

Herpes simplex virus (HSV) oral infection

'Cold sore'; HSV 1 & 2; dormant in trigeminal ganglion; recurrences = herpetic stomatitis (vesicles at lip/vermilion)

Where does HSV lie dormant?

Trigeminal ganglion (CN V)

Fordyce spots

Enlarged sebaceous glands → small white-yellow papules (cheek, lip); normal variant (~70% of people)

Frictional keratosis

Gray-white lesion with epithelial tags from habitual rubbing/biting → excess keratinization

Gingivitis

Gingival inflammation from plaque and tartar (red margin); can form periodontal pockets → bone loss (periodontitis)

Gingival stippling

Normal orange-peel texture of healthy gingiva from deep ridges; can indicate mild gingivitis if red

Oral candidiasis

'Thrush'; Candida infection; most common fungal infection in humans; whitish plaques

Black hairy tongue

Elongated, discolored filiform papillae (coffee, smoking, meds) from hyperkeratinization/decreased desquamation

What is a mucosa and what is its most variable layer?

The epithelial lining of any body opening; the epithelium is the most variable layer and a location indicator

Layers of a mucosa and what lies deep to it?

Epithelium, lamina propria, muscularis mucosae; then submucosa (dense irregular CT, may have glands), muscularis, serosa/adventitia

Oral vestibule vs oral cavity proper vs fauces?

Vestibule: between teeth/gingiva and lips. Proper: behind the teeth, for mastication. Fauces: soft palate, glossal arches/tonsils, base of tongue

How do you tell non-keratinized, parakeratinized and keratinized epithelium?

Non: nuclei to the surface, no granules. Para: pyknotic apical nuclei, few granules. Keratinized: no apical nuclei, stratum granulosum with granules

What is desquamation and why does it happen?

Shedding of surface cells; the epithelium is avascular so cells far from blood supply die

High-friction vs low-friction ET–CT junction?

High: deep interdigitating ridges, large collagen fibers (gingiva). Low: smooth, few ridges (cheek)

Lining, masticatory, specialized mucosa: percent, epithelium, sites?

60% non-keratinized SSE (cheek, lip, alveolar, ventral tongue, floor, soft palate); 25% PKSSE/KSSE (attached gingiva, hard palate, dorsum of tongue); 15% PKSSE/KSSE with papillae (dorsal/lateral tongue)

Three regions of the lip?

Skin (KSSE, hair, sweat and sebaceous glands), vermilion (thin KSSE, no glands/hair, many vessels), inner mucosa (SSE, labial salivary glands)

Why is the vermilion red?

Thin epithelium over many superficial blood vessels

Cheek layers?

Non-keratinized SSE, short ridges, buccal mucous glands, buccinator, skin