Specialised tissues Flashcards
Why do epithelial cells form layers?
Because they form stable cell-cell junctions
Why do epithelial cells form layers?
Because they form stable cell-cell junctions to allow cohesive layers to be formed.
Where are the cell-cell junctions in epithelial cells found?
Apical region of cell-cell contact as a junctional complex
What are the two forms of cell-cell junction?
Zonulae (belts) and Maculae (spots).
What is the arrangement of the junction complex?
Apical —> Basal
- Tight Junction
- Adhesion Belt
- Desosomes and gap junctions
What is the function of a gap junction?
To communicate between cells.
What is a tight junction?
It is a belt junction because it is a zonula (occludens), there are many points where adjacent membranes form v close contacts which are in a network sealing the paracellular pathway.
More elaborate network = tighter seal
What is the function of a tight network?
Seals paracellular pathway
Segregates membranes: stops proteins diffusing through membranes, thus allows adjacent cells to be different + polarity established.
What are the kiss points on a tight junction?
They are a linear array forming network of integral membrane proteins that hook up with membrane proteins on adjacent cells.
What is the adhesion belt?
Zonula adherens
Formed basal to apical tight junction
What are cadherins?
They bind to similar molecules on adjacent cell and cluster with the help of actin to form adhesion belt junction.
What is the actin cytoskeleton closely associated to?
The adhesion belt junction
When epithelial cells first touch what junction is first to form?
The adherens junction, then others form after.
What is the desmosome?
Macula adherens
The SPOT JUNCTION
What are desmosomal cadherins used for?
Involved in transmembrane cell adhesion
Link to intermediate filament cytoskeleton (cytokeratin in epithelium)
