Structure Of The Oral Mucosa

• What is the oral mucosa?

  mucous membrane lining the oral cavity

  
• what does the oral mucosa include?

  - upper and lower labial mucosa (lips)

  - upper and lower labial sulcus

  - free and attached gingiva

  - buccal sulcus

  - buccal mucosa

  - hard palate

  - soft palate

  - dorsum (top) of the tongue

  - ventral (under) surface of the tongue

  - floor of mouth

  
• What is the anterior boundary of the oral mucosa?

  Vermilion (paler) Border of the lips

  
• What is the posterior boundary of the oral mucosa?

  It ends at the anterior pillar of the faucets or the (palatoglossus)

  
• what does mucosa include?

  - the epithelium

  - the underlying lamina propria (in oral cavity it can be called corium)

  
• is under the oral mucosa layer?

  submucosa

  
• Where does the oral mucosa end and submucosa begin?

  It's subjective (blurred)

  -> but when you see other tissues including fat & skeletal muscle, that is submucosa territory

  
• What are rete processes (rete pegs)?

  The epithelial ridges that dive deep into the connective tissue (lamina propria)

  
• What are the connective tissue papillae?

  Fingerlike extensions of the connective tissue that extend up into the epithelium tanentually

  
• what type of epithelium is part of the oral mucosa?

  Stratified squamous epithelium
• What are the layers of Stratified squamous epithelium?

  - Stratum corneum (keratinised)

  - Stratum granulosum

  - Stratum spinosum

  - Stratum basale

  
• describe Stratum corneum (keratinised)

  - cells have lost all their organelles

  - cells are flattened and tightly packed

  - thickeness of this layer varies depending on its region and it varies between individuals

  
• What is parakeratinisation?


  Pattern of keratinisation where nuclei are preserved at the surface

  
• What is orthokeratinisation?


  Pattern of keratinisation where there is a lack of nuclei in the stratum corneum

  
• What is the cornified envelope?

  as a cell matures from the granular to the cornified layer, Filaggrin protein forms tight complex with other proteins (loricrin, involucrin, etc.) and they envelop the bundles of keratin filaments and merge with the cell membrane of the cells that are maturing at the cornified layer. This complex forms what is known as the cornified envelope

  
• What is the cornified envelope important for?

  It's key to providing the structural integrity of the cornified layer, giving it a relative water proofing as well as being able to withstand abrasive forces
• in relation to dentistry:

  
  

  when a tooth is lost/removed, it leaves an edentulous zone.

  the zone will have a slightly white area that goes onto a slightly pink area. what is at these areas?


  ---> white area= region of hyperkeratosis

  (thick degree of orthokeratinatison)

  - increased layer of surface keratin

  
  

  ---> pink area= parakeratinised zone

  
• describe Stratum granulosum

  - as we go up towards the Stratum corneum (keratinised) layer, cells begin to flatten and nuclei begin to degenerate

  - contains Keratohyaline granules

  
• What are the granules within the granular layer?

  Keratohyaline granules
• What do keratohyaline granules contain the precursor to?

  A protein called filaggrin
• describe the Stratum spinosum (prickle cell layer)

  - larger cells than that of basale layer

  - polygonal

  - nuclei are larger but paler than basale cells

  - nucleoli tend to appear in the prickle cell layer

  
  

  - has intercellular bridges between cells (prickles)- preparation of slides artefact: desmosomes remain intact when cells separate away

  
• what is one of the protein components of desmosomes in Stratum spinosum (prickle cell layer)?

  desmoglein
• in relation to dentistry:

  
  

  What is pemphigus?

  Autoimmune disorder; patients develop antibodies to the desmoglein protein (which helps make up desmosomes), so there is a breakdown in desmosomes, resulting in the breakdown in intercellular cohesion of the prickle cells- acantholysis.

  
  

  As it continues to break down, gaps will appear in the prickle cell layer, resulting in a blister

  
• in relation to dentistry:

  
  

  What is acantholysis?

  Loss of intercellular cohesion between keratinocytes

  ( leading to gaps in the prickle cell layer)

  
• describe the Stratum basale layer

  - short columnar to cuboidal in appearance

  - hyper chromatic (nuclei stain darker with hematoxylin)

  - composed of a single layer however this is not regularly seen in tissue sections due to section preparation

  - Basale cells are attached to the underlying lamina propria at the basal lamina

  
• what do basale cells attach to the basal lamina through?

  hemidesmosomes

  
• what are the two layers of the basale lamina under electron microcopy?

  - lamina lucida

  - lamina densa

  
• what is under the basal lamina?

  anchoring fibrils of collagen that loop between collagen fibrils of the lamina propria.

  
• what manufactures the proteins in the basal lamina?

  mostly by the basal epithelial cells (one of which is the bullous pemphigoid antigen) which helps anchor the basal cell to the basal lamina
• What is mucous membrane pemphigoid?

  Autoimmune condition where the patient's own immune cells manufacture antibodies against the bullous pemphigoid antigen, thereby weakening the adhesion between the epithelium with the underlying lamina propria
• in relation to dentistry:

  What is the clinical significance mucous membrane pemphigoid?

  You get a split between the epithelium & underlying lamina propria at the junction between the basal cells & the underlying lamina propria through the basement membrane region.

  
  

  -> This split results in the formation of vesicles, bulla & blisters so it can manifest as desquamative gingivitis.

  
• What is a sign of abnormality in stratified squamous epithelium?

  Mitotic figures in the prickle cell layer (stratum spinosum)
• Where does proliferation occur in stratified squamous epithelium?

  Proliferation occurs in the basal & immediate suprabasal zones

  - so mitotic figures can be found in the basal & immediate suprabasal zones

  
• where does maturation occur in stratified squamous epithelium?

  maturation occurs from the prickle cell layer (stratum spinosum) upwards towards the surface

  
• describe proliferation and maturation in stratified squamous epithelium

  Stratum basale comprises both stem cells and transit amplifying cells.

  ----> as a stem cell divides, one stays as a stem cell and the other becomes a transit amplifying cell which then matures up the layers of stratified squamous epithelium.

  
• What happens as the basal cell moves to the cornified layer, as a general rule of thumb?

  - it becomes terminally differentiated

  - it loses a lot of its organelles & metabolic function

  - the nucleus becomes less pronounced
• what are the 3 regional mucosas of the oral mucosa?

  - masticatory mucosa

  - lining mucosa

  - specialised mucosa
• Which types of mucosa cover which parts of the of the oral mucosa?

  
• what does the masticatory mucosa cover?

  - hard palate

  - gingiva

  
• what does the lining mucosa cover?

  - buccal mucosa

  - buccal sulcus

  - labial mucosa

  - ventral tongue

  - floor of mouth

  - soft palate