Epithelial Tissue

• Cells secrete ECM for:

  • Support & structure
  • Regulation of cell communication & behaviour
• Extracellular matrix (ECM) is crucial to maintain:

  • Differentiated state of cells
  • Normal overall development
• Epithelial tissue:

  • Lines organs & cavities within the body
• Epithelial cell shapes:

  • Squamous
  • Cuboidal
  • Columnar
• Epithelial tissue cell layers are?

  • Simple (1 layer)
  • Stratified
  • Pseudo-stratified = look columnar, but are 1 layer
  • Transitional = more than 1 type (prevents leakage)
• 3 types of classification for epithelial tissue:

  1) Morphology

  2) Surface specialisations

  3) Surface (covering) vs glandular (secretory)
• Glandular epithelium:

  • Single cells = goblet cells (in DS & RS) or
  • Grouped together
• • Tight Junctions/Zonula Occludens = binds cells apically
  • Zonula Adherens = connect by actin
  • Gap Junctions = communication
  • Desmosomes = anchor cells together
  • Hemidesmosomes = anchor cell to basement membrane
• Tight junctions =

  • Controls paracellular (bw/ cells) pathway
  • Selective
  • Proteins = occludin & claudins
• • Claudin-16 = permeable to Mg
  • Claudin-1 = for waterproofing of skin
• Zonula Adherens links cytoskeleton of adjacent cells by actin
• Zonula Adherens protein = cadherins

  • Linked to metastasis of cancer cells (= breaking apart & growing)
• Desmosomes link cytoskeletons of adjacent cells; connect to cytokeratin (intermediate filaments)
• Desmosomes protein = desomglein 3

  • Keeps cells bound together to maintain structural integrity
• Hemidesmosomes anchor to basement membrane, binding to cytokeratin
• Gap Junctions = communication
• Epithelial tissue is polarised

  • Have apical and basal surface
• Microvilli:

  • Fingerlike projections of plasma membrane
  • Short = 0.5-1um
  • Increases SA (for absorption)
  • Core of actin (link into ZA)
• Cilia:

  • Motile = beat in rhythm
  • Move substances across epithelium
  • 10um long
  • Core of microtubules
• Basement membrane:

  • Binds epithelial cells to CT
  • sheet-like arrangement of ECM proteins
  • Forms barrier
  • Controls growth & differentiation
• 3 layers of BM:

  1) Lamina lucida (clear)

  2) Lamina densa (electron dense)

  3) Lamina fibroreticularis (connecting w/ fibres of CT)
• What acts as a protective barrier?

  • Junctional complexes
  • Basement membrane
  • Stratified & transitional epithelium
• What absorbs substances from the apical surface & pass to underlying tissues?

  • Microvilli
  • Basal foldings
  • Basement membrane
• Stem cells play crucial role in tissue renewal & repair
• Epithelial have highest regeneration & turnover capacity
• Epithelial Tissue covers the external body = protective barrier
• Epithelial Tissue is classified based on:

  • Layers, shapes
  • Surface specialisations
  • Function
• Epithelial Tissue: Has polarity (apical & basal surfaces)
• Epithelial Tissue's basement membrane acts as a scaffold & anchors to underlying CT
• Epithelial Tissue are regenerative
• Epithelial Tissue is avascular and gets nutrients via diffusion
• Gap Junctions main transmembrane protein = connexins and form channels (connexons)
• Desmosomes main transmembrane protein = cadherins such as demoglein
• Zonula Adherens main transmemrane proteins = E-cadherins
• Hemidesmosomes main transmembrane protein = integrins
• Surface specialisations:

  • Microvilli = increase SA
  • Cilia = movement of luminal contents
• Stem cells are capable of dividing & renewing themselves, unspecialised and give rise to specialised cell types
• Somatic/Adult Stem cell are undifferentiated cells in a particular tissue = multipotent
• Somatic/Adult Stem primary role is maintenance & repair
• Embryonic Stem cells can become all types of cells in body = pluripotent