Histology of Oral Structures

Key questions

1. Q1What are the functions of the oral cavity?

   Gateway to the digestive system; articulation and resonance of sound (speech); secondary roles in respiration and defense.
2. Q2Name the three spaces of the oral region.

   Vestibule (between lips/cheeks and teeth), oral cavity proper (inside the dental arches), and pharynx.
3. Q3List the structures covered in this lecture.

   Lips and cheeks, teeth and gingiva, hard and soft palate, tongue (papillae, taste buds, lingual tonsils), salivary glands, and the pharynx.
4. Q4How does oral mucosa differ from skin epidermis?

   Stratified squamous but mostly non-keratinized with no zonation (no strata); wet; and highly permeable, especially in the floor of the mouth and ventral tongue. Masticatory surfaces (gingiva, hard palate, dorsal tongue) may be keratinized.

Key questions

1. Q5Describe the three surfaces of the lip.

   External: skin — keratinized stratified squamous with hair and sweat glands. Vermilion (red zone): transition from keratinized to non-keratinized, abundant capillaries, no hair or sweat glands. Internal: typical oral mucosa.
2. Q6Why is the inner cheek mucosa tethered to muscle at intervals?

   It forms many small folds instead of one large bulging fold that could be caught between the teeth.
3. Q7Hard vs soft palate: extent, lining and glands?

   Hard: bony anterior 2/3, separates nasal and oral cavities; keratinized mucosa tightly bound to periosteum; many minor mucous glands. Soft: posterior 1/3, separates nasopharynx from oropharynx; ends in the uvula; many taste buds.
4. Q8What is the gingiva, and what lines the gingival sulcus?

   Oral epithelium firmly bound to the periosteum of the alveolar processes. The sulcus (space between free gingiva and crown, with a cuticle at its base) is lined by non-keratinized epithelium.
5. Q9Why does the vermilion look red?

   Abundant dermal capillaries under a thin, transitional epithelium.

Key questions

1. Q10How many permanent and deciduous teeth are there, and how are the permanent ones grouped?

   32 permanent (8 per quadrant): incisors 8 (cutting, 1 root), canines 4 (grasping, 1 root), premolars 8 (grinding, 2 roots), molars 12 (grinding, 2–3 roots). 20 deciduous teeth; permanent molars have no deciduous precursor.
2. Q11Name the regions of a tooth.

   Crown (enamel-covered, above the gingiva), root (cementum-covered, in the alveolar socket) and neck (cemento-enamel junction).
3. Q12What is enamel made of, what makes it, and why can't it repair?

   95% hydroxyapatite (hardest, most calcium-rich tissue), as tightly packed enamel rods through its full thickness. Made by ameloblasts, which degenerate at eruption — so enamel cannot regenerate.
4. Q13Describe dentin and odontoblasts.

   Dentin: hard but resilient, 70% mineral. Odontoblasts line the inner (pulp) surface, make predentin (type I collagen) that mineralizes, and send processes into dentinal tubules. They are long-lived, so dentin keeps forming and the pulp shrinks.
5. Q14What is in the pulp, and why is pulpitis so painful?

   Gelatinous, highly vascular and innervated CT (all afferents are pain fibers), entering through the apical foramen. Pulp sits in a rigid chamber, so inflammatory swelling compresses nerves → toothache.
6. Q15What anchors the tooth in its socket?

   Cementum (bone-like, made by cementocytes) on the root receives Sharpey's fibers from the periodontal ligament (dense CT, the periosteum of the alveolar bone), which attaches to the alveolar (woven) bone. The PDL is a shock absorber.
7. Q16Order the layers of a developing crown from the surface inward.

   Ameloblasts (if still present) → enamel → dentin → predentin → odontoblasts → pulp.
8. Q17When does tooth development start, and what are its stages?

   Weeks 6–7 of gestation; bud → cap → bell. Crown forms before root; root forms with eruption. Permanent buds stay dormant until after birth.
9. Q18Which embryonic tissue makes each dental tissue?

   Enamel organ (ectoderm, down-growth of oral epithelium) → ameloblasts → enamel. Dental papilla → odontoblasts (dentin) + pulp. Dental sac (mesenchyme) → cementoblasts + periodontal ligament.

Key questions

1. Q19How is the tongue built?

   Interlacing skeletal muscle in three planes (triplanar — high yield) covered by mucosa. Dorsal surface: thick keratinizing epithelium with papillae. Ventral surface: smooth, thin, permeable.
2. Q20What divides the anterior 2/3 from the posterior 1/3, and what covers each?

   The V-shaped sulcus terminalis. Anterior 2/3 (oral part): lingual papillae. Posterior 1/3 (pharyngeal part): lingual tonsils (cobblestone look).
3. Q21Compare the three main papillae.

   Filiform: most numerous, conical, keratinized, no taste buds. Fungiform: mushroom-shaped, scattered (especially at the tip), a few taste buds. Circumvallate: 10–12 large papillae in a V just in front of the sulcus terminalis, each with a moat; over half of all taste buds.
4. Q22What are von Ebner's glands?

   Serous minor salivary glands beneath the circumvallate papillae that flush the moat (cleansing, so new tastants reach the buds). The only serous minor salivary glands.
5. Q23Describe a taste bud.

   Intraepithelial ellipsoid of ~50 spindle cells: light (sensory/gustatory), dark (support) and basal (stem) cells. Sensory cells live ~10 days, have microvilli in the taste pore, and synapse on gustatory nerve fibers.
6. Q24Which five tastes are detected, and where besides the tongue are taste buds found?

   Sweet, sour, salty, bitter, umami. Also in the soft palate (and uvula), pharyngeal wall, epiglottis and larynx; a few in lips, cheeks and upper esophagus. Numbers fall with age.
7. Q25What is unique about lingual tonsils?

   Sub-epithelial lymphoid nodules in the posterior tongue; each has one deep crypt, and minor salivary glands empty into the crypts (unlike other tonsils).

Key questions

1. Q26What is saliva made of, and what does it do?

   About 95–99.5% water, plus proteins (amylase, mucus, IgA, lysozyme, lactoferrin) and electrolytes (K⁺, Ca²⁺, HCO₃⁻). Moistens, lubricates, starts digestion and protects (immune). ~1 L per day.
2. Q27Major vs minor salivary glands?

   Major (parotid, submandibular, sublingual): grossly visible, encapsulated, secrete on demand. Minor: small, unencapsulated, in the submucosa of lips, cheeks, palate and tongue, short ducts, continuous secretion; mostly mucous (von Ebner = serous).
3. Q28Name the four cell types of the major glands.

   Serous cells (zymogen granules; water, electrolytes, amylase, IgA, lactoferrin), mucous cells (mucin), myoepithelial cells (squeeze saliva out), plasma cells (IgA).
4. Q29How do serous and mucous cells look on H&E?

   Serous: dark, granular (zymogen granules) with round central nuclei. Mucous: pale and foamy with flattened basal nuclei. Serous demilunes are serous caps on mucous acini. Myoepithelial cells wrap around the acini.
5. Q30Describe the two stages of salivary secretion.

   1) Acini make the primary secretion (helped by myoepithelial cells). 2) Striated ducts — columnar cells with basal folds full of mitochondria — modify it by active electrolyte transport.
6. Q31How does the autonomic system control saliva?

   Parasympathetic → copious, watery saliva. Sympathetic → scant, thick, viscous saliva ("dry mouth").
7. Q32Give each major gland's share of saliva, secretion type and duct.

   Parotid ~25%, all serous, Stenson's duct (opposite upper 2nd molar). Submandibular ~70%, mixed mainly serous with frequent serous demilunes, Wharton's duct (floor of mouth). Sublingual ~5%, mixed mainly mucous, Bartholin's/multiple ducts behind Wharton's.
8. Q33How do you tell the three major glands apart on a slide?

   Parotid: all serous, heavy capsule, abundant fat, many intercalated + striated ducts. Submandibular: mixed, serous demilunes are diagnostic, little fat. Sublingual: mostly pale mucous acini, no capsule, no fat, rare striated ducts.

Key questions

1. Q34What does the oropharynx do, and what lines it?

   Conducts food from the oral cavity to the esophagus; non-keratinized stratified squamous epithelium (abrasion-resistant).
2. Q35What does the nasopharynx do, and what lines it?

   Conducts air from the nasal cavity to the larynx and trachea; pseudostratified ciliated columnar (respiratory) epithelium.
3. Q36What separates the nasopharynx from the oropharynx?

   The soft palate, which rises during swallowing to close off the nasopharynx.
4. Q37Which tonsils guard the pharynx?

   Pharyngeal tonsil (adenoids) in the nasopharynx, palatine tonsils in the oropharynx, and lingual tonsils on the posterior tongue — together Waldeyer's ring.