Wk2 L2 - Epithelium 1 Flashcards
LO
To know and understand the special features of epithelial cells and tissues.:
* Cellularity
* Polarity
* Specialised contacts
* Lateral communication
* Basal Lamina
* Cell Replacement
To know and understand the special structural features of epithelial cells and their functions.
* Microvilli
* Stereocilia
* Cilia
Specialised junctions
* junctional complex – Tight Junction, Adherens Junction, Desmosomes
* gap junctions
* hemidesmosomes
* focal adhesions
To be able to recognise the special structural features of epithelia in electron micrographs.
Epithelium polarity
Apical
Lateral
Basal
Apical Surface
- Faces external environment/ lumen
- Surface modifications contribute to function (absorption, secretion, protection)
Plasma membrane contains:
- Special proteins and carbohydrates within bilayer membrane
- Transproteins and Channels
Apical surface - Different Projections
Microvilli
Stereocilia
- long microvilli (NOT cilia)
Cilia
- longer and move
Microvilli
- Smallest projections
- Increase SA for absorption
- See in EM clearly
- Fuzzy boarder on cell in LM (brush)
- Contain actin filaments in their core
- Actin filaments interact in a terminal web on the apical region of the cell, under the microvilli
Stereocilia
- long immotile microvilli
- Contain actin filaments in the core
- Under a LM looks like paintbrush hairs
- Often found in genital tract
- Within inner ear (specialised receptors for hearing)
Cilia
- Long projections ~10 µm long
- motile cellular processes “beat”
- Seen in LM as paintbrush hairs with a dark line underneath
- Contains tubulin (anchors to basal body)
Cilia structure
- Contain Tubulin in the core
- Have a 9+2 “axonemic” structure (double tubulin structure next to eachother in centre)
[Heft]
Function of Cilia
- ‘Beat’ in one direction (move fluid)
-Prominant in respiratory system (damaged smoking) - Female reproductive tract (Uterine tube, transport egg and fluid toward uteris)
- Single cilia (hair cells of ear)
Specialisations - Basal PM
Attach epithelium to underlying CT
- Hemidesmosomes
- Focal Adhesions
- Pedicles
- Membrane folding
Hemidesmosomes
- Half of a desmosome, 1 plaque
- Anchors intermediate filaments to cytoskeleton
- Anchors into basal lamina (NOT other cells)
- Common in sites of mechanical stress
Focal Adhesions
- Found on basal membrane
- Anchor actin filaments to basal lamina
- Formed by integrins by linking proteins
- Involved in cell migration
Pedicles
- Means ‘little foot’ on podocytes
- Found in kidney
- Small irregular cytoplasmic projections
- Increase SA to adhere
- Hold cell to Basal Lamina
Basal infoldings
- Increase SA for transport proteins and channels
- Mitochondria typically located in folds (engergy needed for active transport)
