Intercellular junctions
These are several types of membrane modifications that present on the lateral membranes of many epithelial cells
Zonula
occludens/ occluding or tight junctions
It forms a collar around each
cell immediately beneath the cell surface( apical region).
It is impermeable limiting the movement of water & other molecules through the intercellular space
Zonula
adherens
•
This junction encircles the cell and provides for the adhesion of one
cell to its neighbor.
•
The intercellular space of zonula adherens contain a relatively
electron-lucent material of unknown composition which forms a strong bond
between the opposing membrane surfaces.
•
The cytoplasmic aspect of the membrane provides anchorage for the fine
meshwork of microfilaments making up the terminal web
• The terminal web: is a specialization of the actin cytoskeleton lying immediately beneath the cell surface.
Desmosomes
• It is a disk-shaped structure at the surface of one cell that is matched with an identical structure at the surface of the adjacent cell.
• The cell membrane in this
region are very straight and are frequently some what further apart.
• Desmosomes numbers are greatest in stratified squamous epithelia, providing structural integrity at surfaces subject to considerable mechanical stress
Electron microscopic
features of gap junctions
•
Cell membranes of
adjacent cells are closely apposed
•
Connexon:
individual unit of the gap junction
•
Connexins: each
connexon is form by six gap junction protein, which join together leaving a hydrophilic
pore
•
Location: any where along the lateral membranes of epithelial cells.
•
Function: creates a conduit between two adjacent cells for passage of
small ions and informational micro molecules
•
It is found in nearly all mammalian tissues except skeleton muscle.
Examples: cardiac muscle, embryonic epithelia
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