Junctional complex of intestinal epithelial cells, TEM, 15,000x
- Another lateral specialization of epithelium that helps it form a tight
barrier is the junctional complex (terminal bar).
- The tight junction (zonula occludens) is the most apical junction
and it encircles the cell and seals off the space between cells. Freeze
fracture reveals interlocking grooves between the cells. The more of these
fusion points, the tighter the epithelial cells are connected.
- The adherent junction (zonula adherens) is generally next. It
too surrounds the cell like a belt but there is a 20-25nm space between
the cells. Actin filaments from this junction insert into cytoplasmic plaques.
- The desmosome (macula adherens) is a spot junction. It allows
for firm adhesion between cells, especially in the skin and other tissues
that are subjected to much mechanical stress. A hemidesmosome connects
cells to the basal lamina. The cell membranes are about 30nm apart. Filaments
insert into an attachment plaque on the inner leaflet of the plasma membrane.
What exactly do zonula and macula mean?
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