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Oral Mucosa and Salivary Glands

Unit #10

Oral Mucosa

Definition: The moist lining of the oral cavity. Made of two main components:
- Epithelium
- Underlying Connective Tissue
Classification: Three types based on function:
  1. Masticatory Mucosa
     - Includes:
       - Gingiva (free & attached) facing the oral cavity
       - Hard Palate
  2. Lining Mucosa
     - Covers at least 60% of the oral cavity
     - Includes:
       - Lips
       - Cheeks
       - Floor of the Mouth
       - Soft Palate
       - Ventral Surface of Tongue
  3. Specialized Mucosa
     - Located on the Dorsum of the Tongue (home to taste buds)

Components of the Oral Mucosa

Oral Epithelium (Stratified Squamous Epithelium):
- Consists of keratinocytes
Underlying Connective Tissue:
- Known as Lamina Propria
Submucosa:
  - Contains minor salivary glands, fatty tissue, major blood vessels, and nerves
  - Attaches the mucosa to underlying bone or muscle
  - Absent in the Hard Palate
  - Interface between epithelium and connective tissue is formed by the Basement Membrane (Basal Lamina)
  - Rete Pegs: Wavy appearance increasing surface area for vascular and nerve contact

Stratified Squamous Epithelium (SSE)

Hierarchical arrangement of epithelial cells into layers or strata
Continuous Shedding and Renewal:
- Cells shed from surface; renewed by lower layers
Two Types of SSE:
1. Keratinized
2. Non-keratinized

Keratinized Stratified Squamous Epithelium

Lines the masticatory mucosa and specialized mucosa of the tongue
Composed of four layers:
  1. Keratinized Layer (Stratum Corneum)
  2. Granular Layer (Stratum Granulosum)
  3. Prickle Cell Layer (Stratum Spinosum)
  4. Basal Layer (Stratum Basale)
Layer Characteristics:
  - Basal Layer: Adjacent to the basement membrane
  - Prickle Layer: Noted for its spiny appearance
  - Granular Layer: Contains keratohyaline granules aiding in waterproofing
  - Keratinized Layer: Composed of dead cells (corneocytes) containing keratin, providing a mechanical barrier

Types of Keratinization

Orthokeratinized Layer:
- Cells of stratum corneum are non-vital (no nuclei)
- Flat cells located on palms, soles, masticatory mucosa (hard palate, gingiva, dorsum of tongue)
Parakeratinized Layer:
- Cells of the stratum corneum retain degenerating nuclei
- Found in traumatized areas of the hard palate or gingiva

Non-keratinized Stratified Squamous Epithelium

Lines approximately 60% of oral mucosa including:
  - Buccal Mucosa
  - Labial Mucosa
  - Soft Palate
  - Alveolar Mucosa
  - Ventral Surface of Tongue
  - Floor of Mouth
Layers of Non-Keratinized SSE:
  - Surface Layer: Flat, living, nucleated cells
  - Stratum Spinosum (Intermedium): Contains rounded cells
  - Basal (Stratum Basale): Basal layer of cuboidal cells

Masticatory Mucosa Layers

Stratum Basale: Cuboidal or columnar cells attached to basal lamina by hemidesmosomes
Stratum Spinosum: Also known as prickle cells
Stratum Granulosum: Contains keratohyaline granules
Stratum Corneum: Hyperkeratinized surface; nuclei missing, cells non-vital

Masticatory Mucosa: Free and Attached Gingiva

Keratinized? Yes
Sulcular Epithelium: Keratinized status unknown
Junctional Epithelium: Keratinized status unknown
COL Area: Keratinized status unknown

Masticatory Mucosa: Hard Palate

Features:
  - Keratinized stratified squamous epithelium
  - No submucosa present
  - Includes traction bands (bundles of fibers) that anchor palatal mucosa to the underlying bone

Lining Mucosa

Location: Lips, soft palate, buccal mucosa, ventral surface of tongue, floor of mouth
Structure: A layer of epithelium, underlying lamina propria, and submucosa
Characteristics:
- Soft, pliable, and non-keratinized
Epithelial Composition:
  - Stratum Basale: Basal layer of cuboidal cells
  - Stratum Intermedium (Spinosum): Oval and flattened cells
  - Stratum Superficial: Flattened live cells containing small oval nuclei

Lining Mucosa of Lips

Inner Oral Surface: Lined with stratified squamous non-keratinized epithelium
Lamina Propria: Contains small round minor salivary glands
Submucosa: Contains orbicularis oris muscle fibers and minor salivary glands
Red Border: Known as the ________________, it is keratinized
Sebaceous Glands: Located at the angles of the mouth, known as ________ ____________.

Lining Mucosa of Soft Palate

Characteristics: Highly vascularized, pinker due to abundant blood vessels in lamina propria
Submucosa: Contains muscle fibers and minor salivary glands

Lining Mucosa of Cheeks (Buccal Mucosa)

Structure:
  - Non-keratinized stratified squamous epithelium
  - Lamina propria
  - Submucosa containing:
       - Fat cells
       - Mixed salivary glands (seromucous)
       - Muscle fibers

Lining Mucosa of Ventral Surface of Tongue

Components:
  1. Non-keratinized stratified squamous epithelium
  2. Lamina Propria
  3. Submucosa containing muscle fibers

Lining Mucosa of Floor of the Mouth

Non-keratinized mucous membrane covers the floor of the mouth
Submucosa: Contains ____________ glands and minor salivary glands

Specialized Mucosa of Tongue

Dorsum Surface: Composed of specialized mucosa
Four Types of Epithelial Papillae:
  1. Filiform
  2. Fungiform
  3. Circumvallate (home to taste buds)
  4. Foliate
Condition known as Hairy Tongue can occur

Non-Keratinocytes in Oral Mucosa

Comprise approximately 10% of mucosal cells:
  - Langerhans Cells: Function in immune response, found in stratum spinosum, rod/racket-shaped with granules
  - Merkel Cells: Spherical tactile sensory cells found in stratum basale
  - Melanocytes: Produce dark endogenous pigment __________, found in stratum basale
  - Immune cells like lymphocytes and polymorphonuclear leukocytes appear in epithelium during inflammation
  - These cells are responsible for immune response and phagocytosis.

Endogenous Melanosis

Definition: Normal melanin pigmentation observed in some oral tissues.

Overview of Oral Mucosa Types

Type:
  - Location:
  - Epithelial Layer:
  - Special Characteristics:
  - Clinically:
  1. Lining Mucosa:
     - Lines cheeks, lips, soft palate, and sublingual area
     - Non-keratinized stratified squamous
     - Compressible and moveable, submucosa present
     - Appears red due to vascularity
  2. Masticatory Mucosa:
     - Free and attached gingiva and hard palate
     - Keratinized stratified squamous
     - Immovable & resistant, CT fibrous & dense
     - Appears white or pale pink, firm when palpated
  3. Specialized Mucosa:
     - Lines the top surface of the tongue
     - Varies in thickness and keratinization, stratified squamous
     - Contains different kinds of papilla

Age Changes in the Oral Mucosa

Oral epithelium becomes thinner.
Atrophy of minor salivary glands leading to drier appearance.
Appearance of calcifications in the lamina propria of the gingiva.
Reduced ability to repair.
Apical migration of gingiva.

Salivary Glands

Definition: Exocrine glands located in the oral cavity, responsible for secreting saliva.
Main Salivary Glands:
  - Parotid Gland
  - Submandibular Gland
  - Sublingual Gland
Major glands together secrete approximately 90% of saliva.
Minor Salivary Glands:
- Small aggregates of secretory tissues, numbering around 600-1000
- Distributed throughout the oral cavity, absent in gingiva and anterior part of hard palate, secreting only 10% of saliva.

Classification of Salivary Glands

Based on type of secretory cells:
  - Serous cells
  - Mucous cells
  - Mixed or Seromucous (including serous demilune)
Functional Classification:
  - Parotid Glands: Serous
  - Submandibular Glands: Mixed
  - Sublingual Glands: Mucous
  - Majority of minor salivary glands are mucous

Structure of Salivary Glands

Composed of secretory end pieces called acini that communicate with the oral cavity through ducts.
The secretion process is facilitated by myoepithelial cells.

Duct System of Salivary Glands

Types of Ducts:
  1. Intercalated Duct
  2. Striated Duct
  3. Excretory Duct
Striated and intercalated ducts form the intralobular duct system.

Serous Cells Characteristics

Shape: Pyramidal
Features:
  - Abundant secretory granules/vesicles in the apical portion; mostly protein ("zymogen")
  - Prominent Golgi apparatus
  - Mitochondria (laterally and basally)
  - High amounts of Rough Endoplasmic Reticulum (RER) densely packed around the nucleus
  - Round nucleus
  - Stains deeply due to high protein content
Function: Secretes serous fluid; primarily produces salivary amylase (ptyalin).

Mucous Cells Characteristics

Shape: Tubular or pyramidal
Features:
  - Abundant mucigen vesicles (unstained or clear appearance) that compress the nucleus and RER
  - Mitochondria present
  - Well developed Golgi apparatus
  - Flattened nucleus
  - Stains lightly due to mucous composition
Function: Releases mucin, contributing to thick and viscous saliva after mixing with oral fluids.

Mixed Secretory End Piece

Function: Contains serous demilune; produces both serous and mucous secretions.

Myoepithelial Cells

Characteristics: Branched, stellate cells located between basal lamina and acinar cells.
Function:
- Contract and squeeze the acinus, facilitating saliva secretion.

Intercalated Duct Cells

Characteristics:
  - Contains lactoferrin and lysozyme
  - Centrally placed nucleus
  - Small amount of cytoplasm, with limited RER and Golgi
  - Few secretory granules

Striated Duct Cells

Characteristics:
  - Receives primary saliva from acini and intercalated duct cells
  - Modifies primary saliva by reabsorbing and secreting electrolytes
  - Striations increase surface area for ion exchange with nearby blood vessels
  - Shape: Columnar
  - Centrally placed nucleus
  - Mitochondria present in basal striations
  - Contains some secretory granules and RER surrounding the nucleus

Major Salivary Glands Size and Saliva Production

Parotids: Largest, approximately 25% of total saliva
Submandibular: Intermediate size, approximately 60% of total saliva
Sublingual: Smallest, approximately 5% of total saliva
Minor Salivary Glands: Contributes about 10% of total saliva.