Lecture 12. Oral tissue and Salivary Glands

vestibule and oral cavity proper

oral mucosa:

epithelium: covers entire oral cavity; mucous type but keratinized in some areas subject (palate and filiform papillae of tongue)
lamina propria: connected to underlying muscle by loose submucosal supporting tissue in mobile areas (soft palate and floor of mouth); overlies bone (hard palate and tooth-bearing ridges) tightly bound to periosteum by thin, dense fibrous submucosa

submucosa: contains numerous small accessory salivary glands of both serous and mucous types

transition zone between hairy skin and oral mucosa; constitutes free vermilion border; devoid of sweat and sebaceous glands, requires continuous moistening
submucosa contains numerous accessory salivary glands of serous, mucous and mixed sero-mucous types.

rugae: folds

crown portion projecting into oral cavity; entirely covered by highly mineralized enamel enamel: calcified prisms held together by calcified interprismatic material; product of ectoderm
dentine: bulk of tooth; mineralized; similar to bone; derived mesenchyme (epitheliomesenchyme cells of neural crest origin)
odontoblasts produce and repair dentine and add secondary dentine reducing pulp cavity
dentine tubules radiate from pulp cavity to periphery of dentine; follow S-shaped course in longitudinal section;
dental pulp: derived neural crest; contains nerve, blood vessels neck of tooth (=cervix) junction of crown and root

root embedded in bony alveolar ridge; alveolus = socket;

cementum: covers dentine in root; produced by cementoblasts on surface of cementum; become cementocytes
peridontal ligament or membrane: connects cementum to bone of socket
perforating fibers (Sharpey's fibers) run obliquely downards from attachment in alveolar bone to anchorage in cementum (a sling for tooth) gingivum= gum:oral mucosa covering upper part of alveolar ridge; forms tight protective cuff around tooth at neck attached gingiva: protective cover of upper alveolar bone; hemidesmosomes: attach epithelium to cementum
free gingiva: cuff around enamel at neck of tooth
cemento-enamel junction: junctional (crevicular) epithelium: from tip of free gingiva to cemento-=enamel junction; reduced to 2 to 3 cells; frequently infiltrated by lymphoid cells
gingival sulcus (crevice): potential space btwn gingival cuff and enamel of crown periodontium: all tissues surrounding and supporting tooth development:

dental lamina: 6 weeks; horseshoe-shaped epithelial ridge sinks into underlying mesoderm; each quadrant develops four swellings
enamel organs: of future deciduous teeth; backward proliferation gives rise to further enamel organs

ameloblasts: tall columnar cells lining concave face of enamel organ; overlying dental papilla; produced enamel; induces formation of odontoblast layer; lays down columns of enamel matrix; undergoes mineralization; dense prismatic structures;
stellate reticulum: main bulk of enamel organ; ECM rich in GAGs; atrophies
stratum intermedium: between stellate reticulum and ameloblast layer; two or three layers of flattened cells
external enamel epithelium

dental papilla: within enamel organ at cup stage; shrinks; becomes dental pulp (delicate supporting CT resembling mesenchyme) contained within pulp chamber and root canals; opens to alveolous through (apical) foramen

odontoblasts: tall columnar (pseudostratified) epithelioid; future dentine-producing cells over apical region of dental papilla; initiate tooth formation by deposition of organic matrix of dentine = predentine (matrix); induces ameoloblasts to lay down enamel; leaves odontoblastic process within fine dentinal tubules: dentine laid down and odontoblast retreats; embedded in dentine; becomes dentine tubule;
secondary dentine laid down after tooth formation; obliterates pulp cavity
cell free zone of Weil: underlying odontoblastic layer; relatively acellular layer between odontoblastic layer and dental pulp

dental follicle: condensation of mesenchyme around whole developing bud; becomes periodontal ligament (membrane); gives rise to cementum

epithelial sheath (of Hertwig): rim of bell of enamel organ continues to proliferate, inducing dentine formation and determining shape of tooth root; disintegrates after outline of tooth completed; gives rise to epithelial rests of Malassez, small clumps of epithelial cells scattered throughout periodontal membrane

succedaneus lamina: produces succeeding (permanent) teeth

sulcus terminalis:
papillae (3 types) foliform: as in foliage (leaf-like); along side of tongue; has taste buds in children on posterior face
filiform: short bristles; thickly keratinized epi
fungiform: red, globular; thin, nonkeratinized epi
circumvallate: row immediately anterior to sulcus terminals; contain most of taste buds; serous glands = von Ebners glands open into base of cleft; lamina propria: collagenous; binds epi to underlying muscle; serous glands

relatively smooth, stratified squamous epithelium over masses of lymphoid tissue containing follicles; indented by epithelial crypts
 

Major: outside wall of digestive (alimentary) tract (canal); attached to lumen by duct; respond to parasympathetic activity; parenchyma (acinar secretory cells); stroma (= trabeculae) subdivide gland into lobules; interlobular ducts divide into intralobular ducts.

secretory unit = tubulo-acinar structure embraced by myoepithelial cells mucous cells: mucigen granules poorly stained; nuclei condensed and flattened against basement membrane
serous cells: zymogen granules basophilic; nuclei rounded with dispersed chromatin; usually occupy more central position within cell
in mixed units  = serous demilunes surround terminal part of mucous acinus ducts of stratified cuboidal epithelia; intercalated ducts: formed from merged secretory units; lined by secretory cells; drain into
striated duct (larger primarily serous glands) of cuboidal cells with deep infoldings of basal plasma membrane and associated mitochondria; large nuclei located in luminal half, modify ionic content of secretion by active reabsorption and further secretion of ions > hypotonic secretion (sodium and chloride ions concentration below plasma; potassium and bicarbonate ions concentration above). Major Salivary Glands: produce 1L saliva per day; primary saliva modified by striated ducts to secondary saliva

parotid: almost exclusively serous; thin, watery secretion rich in enzymes and antibodies; rounded nuclei toward base of serous cells; granular cytoplasm; lateral membranes and lumen indistinct; intercalated ducts

submandibular (= submaxillary): capsule gives rise to septa; subdivides gland into lobes and lobules; coupound tubuloalveolar gland, contains both serous (predominant) and mucous secretory acini with serous demilunes; myoepithelial (basket) cells embrace acini; produces secrtion of intermediate consistency; ducts with pale, eosinophilic cytoplasm and large lumina

sublingual: subdivided by septa; coupound tubuloalveolar gland (mixed) gland; predominantly mucous secretory cells
(flattened dark nuclei against basement membrane; frothy cytoplasm; intercellular borders and lumen apparent) with serous demilunes (vesicular nuclei, granular, basophilic cytoplasm, no intercellular borders); viscid secretion; myoepithelial (basket) cells

Minor
accessory glands: secrete continuously; ducts directly to surface (no large collecting ducts).