Oral Mucosa Flashcards
What’s a mucous membrane?
- Moist lining of body cavities that communicate with the exterior
What’s Oral mucosa?
- Mucous membrane lining of the oral cavity
What are the functions of the Oral Mucosa?
- Protection against compressive and shearing forces
- Barrier against microorganisms and toxins
- Humoral and cell mediated immunological defences
- Minor gland secretions provide lubrication, buffering and antibody secretions
- Sensations of touch, proprioception, pain and taste
What are the types of Oral Mucosa?
- Masticatory Oral Mucosa
- Areas with high compression
- Hard palate and gingiva
- Keratinised epithelium
- Thick Lamina Propria - Lining Oral Mucosa
- Subject to less compression and friction
- Lips/cheeks/alveolar mucosa/soft palate/ ventral surface of the tongue/ Floor of the mouth
- Mobile and distensible
- Non-keratinised epithelium
- Loose Lamina Propria - Specialised Oral Mucosae
- Dorsal surface of the tongue/ Lingual tonsils/ gingival attachment to teeth/ vermillion border
What are the components to Oral Mucosa?
- Epithelium
- Lamina Propria
- Submucosa
Oral Epithelium: What are the regions of Keratinised Epithelium?
- Stratum Germinativum (stratum basale)
- Stratum Spinosum (Prickle cell layer)
- Stratum Granulosum (Granular layer)
- Stratum Corneum (Keratinised or cornified layer)
Oral Epithelium: What are the regions of Non-Keratinised Epithelium?
- Stratum Germinativum (Stratum basale)
- Stratum Spinosum (Prickle cell layer)
- Stratum Intermedium (Intermediate layer)
- Stratum Superficiale
Stratum Germinativum: What are its key features?
- Proginator cells of Keratinocytes
- Single cell layer
- Adjacent to the Lamina Propria and separated by a BASAL LAMINA
- Cuboidal cells
- Mitosis only occurs in this layer
- Least differentiated cells within the oral epithelium
- Stem cells are though to be within the epithelial ridges that project into the underlying lamina propria
What influence do maturing Stratium Germinativum cells have on the nearby cells?
- Maturing cells produce growth inhibitors that restrict further cell division by negative feedback
Stratum Spinosum: What are it’s key features?
- Round or Ovoid cells
- Several layers thick
- Show the 1st stages of maturation
- Larger and rounder than the cells of Stratum Germinativum
- Transition is characterised by the appearance of new Cytokeratin types
- 1st appearance of Involcurin (precursor protein of the cornified envelope eventually found in the cornified layer)
How do the upper layers of the Stratum Spinosum differ?
- Cells appear small and possess Odland bodies (intracellular membrane coating granules rich in phospholipids)
Where do the Odland bodies originate?
- Golgi Apparatus
What’s a defining feature of Stratum Spinosum cells?
- Desmosomes and Spines
- Increased number of desmosomes
- Slight shrinkage that occurs in most histological preparations causes the cells to separate at all points where desmosomes do not anchor together
= GIVES SPINY APPEARANCE
What does the term Parabasal layer refer to?
- Refers to the deepest layer of cells of the Stratum Spinosum that lie next to the Stratum Germinativum
Stratum Granulosum: What are it’s key features?
- Show further increase in maturation
- Many organelles are reduced or lost (cytoplasm occupied by tonofilaments and tonofibrils)
- Larger and flatter cells
- Contain large number of Keratohyaline granules
What do Keratohyaline granules contain?
- Precursor to filaggrin
= Profilaggrin
What’s special about the membrane coating granules?
- They’re discharged into the extracellular space
- Associated with the development of a barrier in the epithelium that limits the movement of substances between the cells
Stratum Corneum: What are its key features?
- Final stage in maturation of keratinsied epithelium
- Epithelial cells have lost all organelles (inc. nuclei & keratohyaline granules)
- Cells filled with closely packed tonofilaments surrounded by the matrix protein filaggrin = COLLECTIVELY CALLED KERATIN
- Can be termed Epithelial squames (these cells can shed)
- The shedding is called DESQUAMTION and is facilitated by desmosomes weakening/disappearing
What feature does Stratum Corneum provide?
- Mechanical protective function to the mucosa
- Varies in thickness (up to 20 cells)
What is Parakeratinised Epithelium?
- Stratum Corneum cells with retained nuclei (albeit small + shrunken)
What is Ortho-keratin Epithelium?
- Stratum Corneum cells without the nuclei
What is Non-keratinised Epithelium?
- 10% of cells in the oral epithelium are non-keratinocytes
- Melanocytes/Langerhans cells/ Merkel cells
- Lack tonofilaments and desmosomes
- Will appear unstained when staining for Cytokeratins
What are Cytokeratins?
- A class of intermediate filaments specific to epithelial cells (cytoskeleton)
- 20 Cytokeratin types (CK 1-20)
Products of 2 gene families which occur in pairs:
- Neutral/basic type II = 1-8
- Acidic type I = 9-20
What are simple Cytokeratins?
- Only expressed in simple epithelia
- CK 7, 8, 18
What are Stratification Cytokeratins?
- Pairs CK 5-14, 4-13, 1-10
What are the functions of Cytokeratins?
- Components of the cytoskeleton and cell contacts (desmosomes and hemidesmosomes)
- Some are important in maintaining the metabolic integrity of the cell
- CK14 related to innervation of the superficial mucosa through signal transduction
What’s the basic distribution of Cytokeratins?
- CK 5 & 14 are restricted to the basal and parabasal layers
- CK 14 can be expressed in surpabasal layers
- CK 1 & 10 OR 2 & 11 are expressed in the suprabasal layers of the masticatory mucosa (associated with terminal differentiation an keratinisation
- Keratin layer is negative (no cytokeratins)
- CK 4 & 13 are present in the supreabasal layer in the lining mucosa
What are CK 16 and 6 associated with?
- Rapid turnover epithelia
What is CK 19 associated with?
- Marker for basal keratinocytes in lining mucosa
What Cytokeratins does the ventral surface of the tongue express?
- CK 5, 6, 14
What Cytokeratins does the soft palate lining express?
- CK 7, 8, 18, 19
What are the clinical considerations related to Cytokeratin expression?
- Their expression can be alter in states of inflammation
- Can be used in diagnostic histopathology
- Dysplastic changes revealed by CK alterations
Non-keratinocytes within Epithelium: What are Melanocytes and what are their functions?
- Melanin producing cells (responsible for skin pigmentation)
- Located in Stratum Germinativum
- Derived from Neural Crest cells - present in skin after 8 weeks intrauterine life
- Melanin is produced using tyrosinase
- Difference in the degree of pigmentation is a result of a combination of size of the cells and the degree of branching - NOT THE ABSOLUTE NUMBER
What is the pigment contained in?
- Small granules called MELANOSOMES
How do Keratinocytes take up melanin?
- Each Melanocyte can contact up to 40 keratinocytes
- Keratinocytes release mediators important for melanocyte function
- Keratinocytes take up melanin by actively phagocytosing the melanocytes dendritic tips
What’s Peutz Jeghers Syndrome?
- Mucoctaneous pigmentation (resembling freckling, appears in infancy)
- Buccal mucosa and lips are mainly affected
- Autosomal dominant
What’s Hyperkeratosis associated with?
- Melanic pigmentation
- Smoking can cause melanocyte activation/reaction to the constant irritation
- Melanin incontience: melanin present in the subepithelial macrophages having leaked out of melanocytes and basal cells
What are Langerhans cells and what’s their function?
- Dendritic, Antigen Presenting Cells (APC’S)
- Located above the basal layer
- Derivative of bone marrow precursors - leaving blood stream and enter Lamina Propria before penetrating Stratum Germinativum
- Important role in contact hypersensitivity reaction of the skin
- Role in anti-tumour immunity
- Role in graft rejection
What are Merkel cells and what’s their function?
- Found in Stratum Germinativum
- Closely apposed to nerve fibres
- Contain CK8/18 & 20
What’s the Lamina Propria?
- Connect tissue underlying the oral epithelium
How many layers does the Lamina Propria have?
x2
- Superficial papillary layer (loose thin collagen fibres)
- Deep reticular layer (thick parallel collagen bundles)
Are fibroblasts present in the lamina propria?
- Yes
- Typical of those found in loose CT
- Constantly producing and secreting extracellular fibres and ground substance
What the composition of Lamina Propria’s Extracellular matrix?
- Collagen (90% type I, 8% type III)
- Non-fibrillar collagen
- Elastin
- Oxytalan
- Proteglycans & Glycoproteins hydrated gel consistency
What are the other cells present in the Lamina Propria?
Macrophages:
- Seen in their fixed, inactive state (known as Histocytes)
- Difficult to distinguish from Fibroblasts (have a smaller+darker nuclei)
- Also Antigen Presenting Cells (APC’S)
Mast Cells
- Mononuclear, spherical/elliptical in shape
- Contain histamine+heparin intracellular granules
- Role in vascular homeostasis
- Type I hypersensitivity
What’s the Epithelial CT Interface?
- A thin layer called the basal lamina (basement membrane
- Consists of fibril and ground substance complex
What are the Basal Lamina’s two zones?
- Lamina Lucida (20-40nm thick), immediately
under the epithelium - Lamina Densa (Deep to the Lamina Lucida)
What’s the origin of the basal lamina components?
- Synthesised by the Epithelial cells
What’s the Lamina Lucida made of?
- Predominantly Laminin (glycoprotein)
- Cements Collagen type IV between Lamina Densa and the Epithelial cells
What’s the Lamina Densa made of?
- Type IV Collagen coated with heparan sulphate
- Thick collagen fibres attach to the lamina densa to link the basal lamina to the CT
- Fibronectin is found and may bind fibroblasts and proteoglycans to the LD
What’s the role of Basal Lamina?
- Provides mechanical adhesion between the epithelium and the CT
- Molecular barrier
- Role in response to tissue injury
