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Salivary Glands and Oral Tissues – Comprehensive Study Notes

Salivary Glands

  • Functions of saliva: discussed in transcript but explicit enumeration is not provided; major glands contribute saliva with serous and/or mucous components across different ducts.
  • Major glands
    • Parotid (serous) – discharges into the oral cavity through Stensen’s duct.
    • Submandibular – mixed, mostly serous – secretion via Wharton’s duct.
    • Sublingual – mixed, mostly mucous.
  • Minor glands
    • Locations: hard and soft palate, tongue, lips.
    • All mucous, except von Ebner’s glands (serous, on the tongue).
  • Structure of salivary glands
    • Acini types
    • Serous acini: composed of pyramidal cells surrounding a central lumen.
      • 8-12 pyramidal cells around the lumen; basal aspect adjacent to stroma; narrow apex contributing to lumen.
      • May have myoepithelial cells at the basal aspect – contractile, may help propel saliva into ducts.
      • Nucleus is round; abundant mitochondria and rough endoplasmic reticulum (RER).
      • Secretory granules accumulate toward the apex.
      • Microvilli present on luminal surface.
      • Intercellular canaliculi present between cells.
      • Secretory products typically more serous in nature.
    • Mucous acini: tubular configuration; appear round in cross-section.
      • Lumen larger than serous acini; large amounts of mucus accumulate toward the apical region.
      • Nucleus appears flattened.
      • May have serous cells associated – demilune (crescent) covering mucous cells at the end of the tubule; secretions reach lumen via intercellular canaliculi.
    • Key distinctions:
    • Serous acini: round nucleus; numerous mitochondria and RER; secretory granules apical; microvilli; intercellular canaliculi.
    • Mucous acini: flattened nucleus; larger lumen; mucus predominates apically; potential serous demilunes.
  • Formation of saliva (two stages)
    • Primary saliva produced by acinar cells and intercalated ducts.
    • Primary saliva is modified in striated and excretory ducts to form final saliva.
  • Production of primary saliva – overview
    • Acinar cells have abundant rough endoplasmic reticulum (RER) and a large Golgi complex.
    • Secretory proteins are synthesized by ribosomes attached to the rough ER and translocated into the ER lumen.
    • Proteins associate with chaperones that ensure proper folding and initiate post-translational modifications such as disulfide bond formation and N- and O-linked glycosylation.
    • Proteins are transported to the Golgi, where they undergo further modification, condensation, and packaging into secretory granules.
    • Secretory granules are stored in the apical cytoplasm until an appropriate secretory stimulus (e.g., sympathetic stimulation via G-protein coupled receptors).
    • In salivary glands, the sympathetic neurotransmitter norepinephrine is usually an effective stimulus for exocytosis.
  • Salivary gland ducts
    • Connective tissue fibers subdivide the glands into lobules containing secretory units and excretory ducts.
    • Intercalated ducts
    • Collect the initial secretions; smallest ducts.
    • Lumen small; lined by low cuboidal epithelium.
    • Myoepithelial cells surround some portions.
    • Striated ducts
    • Formed from merging of several intercalated ducts.
    • Lined by columnar epithelium.
    • Basal infoldings with numerous elongated mitochondria create tiny basal striations (stainable) – corresponding to the striations seen in histology.
    • Excretory intralobular ducts
    • Striated ducts join to form larger intralobular ducts of increasing size.
    • Surrounded by increased layers of connective tissue fibers.
  • Interlobular and interlobar ducts
    • Intralobular ducts join to form larger interlobular and interlobar ducts.
    • Lined with pseudostratified columnar epithelium.
    • Terminal portion conveys saliva from the glands to the oral cavity.
    • Larger interlobar ducts may be lined with stratified epithelium (low cuboidal or columnar).
  • Salivary gland geography – arrangement of acini and ducts
    • Acini distributed within lobules connected to ducts that traverse intercalated, striated, and interlobular/intralobar ducts to drain into the oral cavity.

Tooth Supporting Tissues

  • Cementum
    • Definition and composition
    • Mineralized connective tissue that covers the root dentin.
    • Avascular and aneural connective tissue.
    • Predominantly type I collagen (organic).
    • Cementum types (bold features emphasized): focus on differences among primary and secondary cementum and their functional implications.
    • Cementoblasts: cells located in the periodontal ligament (PDL) space, responsible for cementogenesis.
    • Cementoclasts: cells responsible for remodeling/breakdown of cementum.
    • Cementocytes: regulation of cellular cementum formation and resorption.
    • Acellular, Extrinsic Fibrous Cementum (AEFC / Primary Cementum)
      • Forms slowly; covers cervical ⅔ of the root.
      • Function: anchorage of teeth.
      • No embedded cells.
      • Initial cementum fibers are perpendicular to the cementoenamel junction (CEJ) – fibrous fringe (FF).
      • Extrinsic collagen fibers from the periodontal ligament (Sharpey’s fibers) are stitched to the FF.
      • No well-defined cementoid layer.
    • Cellular, Intrinsic Fibrous Cementum (CIFC / Secondary Cementum)
      • Function: adaptation, repair, attachment.
      • Confined to the apical and interradicular regions of the tooth.
      • Forms rapidly; cementoblasts become entrapped within matrix (cementocytes).
      • Layer of cementoid evident.
      • Extrinsic PDL fibers exist but are not continuous with intrinsic fibers.
    • Acellular Afibrillar Cementum
      • No collagen fibers (no direct role in tooth attachment).
      • Well-mineralized ground substance.
      • Deposited over enamel and dentin along the CEJ.
      • No known function.
    • Cementoenamel junction (CEJ) types and clinical relevance
    • Overlap type: cementum overlaps enamel – approximately 60 ext{ extsuperscript{ extup{(%)}}} and most common.
    • Edge-to-edge type: approximately 30 ext{ extsuperscript{ extup{(%)}}}.
    • Gap type: approximately 10 ext{ extsuperscript{ extup{(%)}}}; exposed dentin and root sensitivity.
  • Alveolar bone
    • The alveolar bone proper
    • Part of the alveolar bone immediately surrounding the root; where PDL fibers insert.
    • Consists mainly of compact bone (dense bone).
    • Also known as bundle bone or lamina dura.
    • Supporting alveolar bone
    • Consists of cortical/compact plates (buccal/labial and palatal/lingual) and the trabecular/cancellous bone between the cortical plates and the alveolar bone proper.
    • Alveolar crest
    • The most coronal part of the alveolar process.
    • The outer cortical plate and socket wall meet at the alveolar crest, typically 1-2 ext{ mm} below the CEJ.
    • Cortical plate thickness
    • Thinner in the maxilla and anterior teeth.
    • Thickest on the buccal aspect of the mandibular posterior teeth (molars and premolars).
  • Periodontal Ligament (PDL)
    • Characteristics and functions
    • Soft, specialized connective tissue located between cementum and the alveolar bone proper.
    • Suspends the tooth within its bony socket.
    • Supplies cementum with nutrients.
    • Cells form, maintain, and repair alveolar bone and cementum.
    • Sensory function (proprioception).
    • Maintains a constant width (space) around the tooth.
    • Cellular composition
    • Most abundant cells: fibroblasts – high protein turnover.
    • The PDL can produce the protein Msx2 to help prevent ankylosis.
    • Innervation
    • Two types: sensory and autonomic.
    • Sensory: nociception and mechanoreception; myelinated fibers mediate pain; Ruffini-like endings are low-threshold mechanoreceptors important for perception.
    • Autonomic: autonomic fibers (sympathetic/parasympathetic) regulate blood flow and glandular activity.
    • Principal (load-bearing) PDL fiber groups and functions
    • Alveolar crestal group: from cementum below CEJ to the alveolar crest; prevents extrusion and resists lateral movement.
    • Horizontal group: from cementum to the alveolar bone just below the alveolar crest; resists horizontal and tipping forces.
    • Oblique group: from cementum to the bone coronally; resists vertical and intrusive forces; largest and most numerous.
    • Apical group: from cementum to the bone at the apical socket; resists vertical force.
    • Interradicular group: between roots of multirooted teeth; resists vertical and lateral forces.
    • Gingival (PDL) fiber groups
    • Trans-septal: extend interdentally from cementum over the alveolar bone crest; embedded in cementum of adjacent tooth.
    • Dento-gingival: from cervical cementum to lamina propria of free and attached gingiva.
    • Alveolo-gingival: from alveolar crest to lamina propria of gingiva.
    • Circular: forms a band around the neck of the tooth, interlacing with other gingival fibers.
    • Dento-periosteal: from cementum to the periosteum of the outer plate of the alveolar process.
    • Clinical implications
    • Hypercementosis: abnormally thickened cementum, often at root apex and interradicular regions or entire root surface.
    • Cementicle: small globular mass of cementum in PDL or attached to cementum; may arise from microtrauma.
    • Cementoblastoma: benign neoplasm producing cementum-like tissue attached to root apex (e.g., mandibular permanent first molar).
    • Hypophosphatasia: reduced activity of tissue nonspecific alkaline phosphatase; reduced cementum formation.

Oral Mucosa (Epithelium + Connective Tissue)

  • Functions of oral mucosa in humans
    • Protection, sensation (temperature, touch, pain, taste), secretion (saliva, sebaceous glands).
    • Absorption/permeability: Permeability is a key feature; greatest in non-keratinized layers; permeable exception is the dentogingival junction.
  • Appearance vs. skin (clinical/histological contrast)
    • Oral mucosa is more deeply colored due to vascularity in the connective tissue; it is moist; lacks skin appendages (no sweat glands or hair follicles).
    • Fordyce’s spots: sebaceous glands in upper lip and buccal mucosa.
  • Epithelium type
    • Stratified squamous epithelium: keratinized or non-keratinized; parakeratinization is normal in oral mucosa but not in skin.
  • Lamina propria and submucosa
    • Lamina propria may be minimal or may include a submucosa depending on region.
  • Keratinized vs non-keratinized oral epithelium: maturation layers in keratinized oral epithelium
    • 4 layers in keratinized epithelium:
    • Stratum corneum (cornified layer) – outermost
    • Stratum granulosum
    • Stratum spinosum (prickle cell layer)
    • Stratum basale – site of cell division in normal state
  • Differentiation proteins and their roles
    • Desmogleins/desmocollin: desmosome formation.
    • Transglutaminases (TGs): catalyze crosslinking of proteins to form the cornified envelope.
    • Filaggrin: precursor (profilaggrin) from keratohyaline granules; promotes aggregation of keratin intermediate filaments and cell flattening.
    • Lipids from membrane-coating granules in the stratum spinosum contribute to the impermeable cornified envelope (lipids + crosslinked proteins).
  • Basal membrane attachments and disease relevance
    • Proteins in basal cells involved in attachment to the basement membrane; melanosomes and premelanosomes relate to pigmentation abnormalities.
  • Layers in keratinized vs non-keratinized epithelium
    • Keratinized: Stratum corneum, granulosum, spinosum, basale.
    • Non-keratinized: superficial layer, intermediate layer, prickle cell layer (spinosum), basal layer.
  • Localization of keratinization
    • Occurs on the dorsal surface of the tongue, hard palate, and gingiva; areas subject to mechanical stress and trauma.
  • Non-epithelial cells in oral mucosa
    • Melanocytes: in basal layer; produce melanin.
    • Merkel cells: tactile sensory cells in basal layer.
    • Langerhans cells: in suprabasal layers; antigen trapping; dendritic/APC function.
    • Lymphocytes: variable locations; participate in inflammatory responses.
  • Basement membrane structure
    • Location: continuous between epithelium and connective tissue lamina propria.
    • Layers: Lamina lucida, Lamina densa, Lamina fibroreticularis.
    • Attachment to basal epithelial cells via hemidesmosomes; integrins with α6 and β4 subunits.
    • Relevant proteins: laminins, integrins, bullous pemphigoid antigens BP180 (collagen XVII) and BP230 (plectin).
  • Lamina propria
    • Connective tissue supporting the epithelium; two principal layers: Papillary and Reticular.
    • Cells: fibroblasts (matrix production, turnover), macrophages (ingestion of debris/foreign material; can be melanophages or siderophages), mast cells, various inflammatory cells (lymphocytes, plasma cells, neutrophils), and other immune cells.
    • Fibers: collagen types I and II; type IV and VII associated with the basal lamina; elastin is abundant in lining mucosa.
    • Ground substance: proteoglycans and glycoproteins.
  • Blood and nerve supply
    • Blood supply: multiple sources; arteries running parallel to the surface; in submucosa or deep reticular layer.
    • Nerve supply: reticular layer of lamina propria houses most nerves; sensory functions predominate; autonomic fibers supply blood vessels and minor salivary glands; response includes sensation of warmth, cold, touch, pain, and taste; temperature reception is greater in the anterior parts of the tongue and hard palate.
  • Tongue structure and specializations
    • Anterior 2/3 vs posterior 1/3 separated at the sulcus terminalis.
    • Dorsal surface: keratinized and gustatory; Ventral surface: non-keratinized.
    • Papillae (locations)
    • Filiform papillae: most numerous; top of the tongue; no taste buds.
    • Fungiform papillae: anterior part of the tongue; contain few taste buds.
    • Circumvallate papillae: back of the tongue; contain thousands of taste buds; surround by trench with von Ebner’s serous glands.
    • Foliate papillae: sides of the tongue; contain taste buds; numbers range from about 12 to hundreds.
    • Taste bud structure
    • Each taste bud contains about 50-150 taste receptor cells (TRCs).
    • Three cell types: gustatory, sustentacular, and basal (which divides to produce the other two types).
    • Apical ends terminate in a taste pore with microvilli.
    • Posterior 1/3 tongue features
    • Characterized by mucosal folds; contains lingual tonsil.
    • Mucous minor salivary glands present; ducts discharge into tonsillar crypts or directly onto the tongue surface.
  • Mucocutaneous and mucogingival junctions
    • Mucocutaneous junction: boundary between skin and oral mucosa.
    • Mucogingival junction: boundary between alveolar and gingival mucosa.
    • Structure and color differences relate to vascularity and submucosa; non-keratinized areas show vascular coloration more clearly.
  • Dentogingival junction
    • Organization and relationships among gingiva, tooth, gingival sulcus, sulcular epithelium, and junctional epithelium (JE).
    • Junctional epithelium
    • Thickness: approximately 12-18 cells.
    • Fewer tonofilaments and desmosomal junctions, contributing to higher permeability.
    • JE cells migrate superficially but do not differentiate to a keratinized surface.
    • High cell turnover; JE cells move coronally with desquamation into the gingival sulcus.
    • JE readily regenerates from adjacent oral sulcular or oral epithelium after damage or surgery.

Skin and Related Structures

  • Skin as an organ
    • The largest organ of the body.
    • Functions: protective barrier, sensory reception, thermoregulation, metabolism, and signaling.
  • Epidermis structure
    • Keratinocytes undergo terminal differentiation (keratinization).
    • Strata (from basal to surface):
    • Basale (stratum basale): mitotically active; attached to basement membrane via hemidesmosomes.
    • Spinosum (stratum spinosum): several layers of polyhedral cells joined by desmosomes.
    • Granulosum (stratum granulosum): keratohyalin granules present.
    • Lucidum (stratum lucidum): present only in thick skin; flat, enucleate, eosinophilic cells.
    • Corneum (stratum corneum): outer, protective layer.
    • Melanocytes: located in stratum basale; produce melanin in melanosomes; UV protection; albinism due to tyrosinase deficiency; variations can lead to nevi or melanoma.
    • Langerhans cells: APCs within the epidermis (primarily in stratum spinosum).
    • Merkel cells: mechanoreceptors in thick and thin skin.
  • Dermis
    • Two major layers: Papillary (superficial, loose CT with microvasculature) and Reticular (deeper, denser irregular CT).
  • Cutaneous sensory receptors
    • Free nerve endings (pain) and Merkel cells (touch) in epidermis.
    • Meissner corpuscles: light touch (in dermal papillae of glabrous skin).
    • Pacinian (Lamellated) corpuscles: large, ovoid, deep in dermis/subcutaneous tissue; detect pressure and firm touch.
    • Krause end bulbs: low-frequency vibration/movements.
    • Ruffini endings: tissue distortion/pressure.
  • Subcutaneous tissue (hypodermis)
    • Loose CT; binds skin to underlying structures; contains adipocytes; rich vascular supply.
  • Epidermal appendages
    • Hair: keratinocytes proliferate in hair matrix; medulla/cortex/cuticle form hair; dermal papilla provides blood supply.
    • Nails: keratinocytes in nail matrix form hard keratin; growth similar to hair.
    • Sebaceous glands: holocrine secretion of sebum onto hair follicles.
    • Sweat glands
    • Eccrine: widely distributed; open onto skin surface; regulate temperature via watery secretion.
    • Apocrine: restricted to axillae and perineum; ducts into hair follicles; develop after puberty; secrete protein-rich sweat onto hair follicles.