Wk3 L1 - Epithelium 2 Flashcards
LO
- To be able to recognise the special structural features of epithelia in electron micrographs.
- To know the different types of epithelial tissues and what is different about them:
Simple
* squamous
* cuboidal
* columnar
Stratified
* squamous
* cuboidal
* columnar
Pseudostratified
.
* To be able to relate, broadly, the type of epithelium to the type of site(s) where it is found and its function.
* To be able to recognise the different epithelial types in histological slides.
Lateral PM specialisations
- Close appositions with adjacent cells
- Adhesive and communicative
Junction Complex order:
- Tigh Junction
- Adherens Junction
- Desmosomes
Localised Junctions:
- Desmosomes
- Gap Junctions
Junction Complex
- Tight Junction = (Zonula Occludens)
- Adherens Junction = (Zonula Adherens)
- Desmosome = Macula Adherens
Tight Junctions
Zonula Occludens:
- Occludes the paracellular space and movement
- Most apical in junction complex
- Different depth and complexities (tight or ‘leaky’)
Integral membrane proteins:
- Occludin
Tight Junction Strands:
- Claudins (regulate permiability)
[HEFT] - EM
Adherens Junction
Zonula Adherens:
- Intermediate Junctiona below tight junctions
- Adhesive belt around apical region of cell
- Anchors terminal web (actin), connects apical cytoskeleton af adjacent epithelial cells by lateral adhesion
- Maintain cell shape and flexability
Cadherins:
- Link cells together intercellularly by linking adherens junctions together
Desmosomes
Macula Adherins:
- 3rd in junction complex, OR at localised junctions
- Discrete spots of cellular movement ‘spot welds’
- Very strong mechanical adhesion
Desmosome structure
- Dense plaque on cytoplasmic side of lateral PM
- Filaments in extracellular space
- Intermediate filaments feed into the plaques, (desmosomes anchor intermediate filaments)
Protein filaments between cells, holding the 2 cells together:
- Desmocollin
- Desmoglein
Gap Junctions
- Localisied Junction
- Communicating junction, nexus (pass on signalling molecules to other cells)
- Discrete spot on lateral PM
- Usually located well below other junctions
- Transport of ions, metabolites and molecules between cells
Connexin Proteins:
- Form connexin channels which molecules can travel through
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Lateral interdigitations
- Infoldings on lateral PM
- Increase SA
- Fit together like a puzzle
Epithelium type and its function
Simple Squamous = Absorption & Secretion
Simple Cuboidal = Absorption & Secretion
Simple Columnar = Absorption & Secretion
Stratisfied Squamous = Protection
Stratisfied Cuboidal = Protection
Simple squamous
Exchange of materials
Often permiable
Special cases:
- Endothelium = Blood vessel linings
- Mesothelium = Lining body cavities & Organ surfaces.
Stratisfied Squamous - Epithelium
Protection - wear & tear
- Desmosomes & Hemidesmosomes very present
- Basal cells - attach to basal lamina
- Rapid turnover
- Found in moist area surfaces
Keratinised Stratisfied squamous epithelium
- Skin & parts of oral cavity
- Keratin, Resistent to abrasion, water insoluble proteins
- Found in areas exposed to air, subject to abrasion
- Contain lots of desmosomes
Simple Cuboidal epithelium
- Absorption and secretion
- Often have microvilli on apical surface
- Ducts, kidney tubules, thyroid follicles
Simple columnar epithelium
- Most polarised (apical region completely different to basal)
- Secretion &/or absorption
- Gut, respiratory, Female reproductive system
Non-ciliated:
- Most of digestive system
- More likely microvilli
Ciliated:
- In areas where substances need to move
- Moves mucus/ occytes
- Airways
- Female reproductive tract
Stratisfied cuboidal and columnar
- Barrier, conduit, Protection
- Rare
- 2-3 cells thick
- Ducts of glands
Layering and shapes of epithelial cells
Some exeptions:
- Pseudostratisfied (lots of nuclei)
- Transitional (Start thick and lining expands with cell numbers decreasing)
Pseudostratisfied epithelium
- Protection and secretion
- Contains nuclei at different hights (looks stratisfied)
- Often have cilia
- All cells lie of basal lamina
- Not all cells same height
eg. trachea and male reproductive system
Transitional Epithelium
Protection, osmotic barrier
Bladder and urinary system
Transtory thickness (Bladder empty Vs Full)
Apical cells
- Dome shaped, binucleated
- Refractile boarder - darker pink layer of plaques
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