36
UNIT 2
Basic Tissues
Figure 3-8A.
Components of the junctional complex.
EM,
3
70,000.
This is a view of parts of two adjacent epithelial cells that line the gallbladder. At the top of the
F
eld, parts of some
microvilli
can be seen at the luminal surfaces of the cells. The three types of
cell junctions that typically compose the
junctional complex
can be distinguished. The
zonula
occludens junction
has branching strands of fusion between the
plasmalemma
of the two cells.
This effectively prevents movement of material across the epithelium by the passage between
adjacent cells. The
zonula adherens junction
provides a collar of mechanical adhesion between
neighboring cells. The cytoskeleton of each cell at the level of the
zonula adherens
consists pre-
dominantly of
actin ± laments
in a network termed the
terminal web
. The third element of the
junctional complex is an array of scattered
desmosomes
(
maculae adherentes
; singular,
macula
adherens
). These provide mechanical adhesion between adjacent cells in spots.
Cytokeratin
±
laments
(
tono± laments
) of the
cytoskeleton
are anchored in the attachment plaques on the
two cytoplasmic surfaces of each
desmosome
.
Figure 3-8B.
Simpli± ed representation of components of the junctional complex.
Intercellular connections of the epithelial cells include (1)
tight junctions
(
zonular occludens
);
(2)
adhering junctions
(
zonula adherens
); (3)
desmosomes
(
macula adherens
); (4)
gap junctions
;
and (5)
hemidesmosomes
. The
junctional complex
is composed of a tight junction, an adhering
junction, and a desmosome. See the chapter introduction for detailed information.
D. Cui
D. Cui
D. Cui
D. Cui
D. Cui
Tonofilaments
Terminal web
(actin filaments)
Terminal web
(actin filaments)
Terminal web
(actin filaments)
Tonofilaments
Terminal web
(actin filaments)
Intramembrane protein
(sealing strands)
Intercellular
space
Tight junction
(zonula occludens)
Adhering junction
(zonula adherens)
Actin
filaments
Intracellular
line protein
Transmembrane
link protein
Desmosome
(macula adherens)
Gap Junction
Hemidesmosome
Intracellular
attachment plaque
Intermediate
filaments
Transmembrane
proteins
Cytoplasm
Connexons
Cell
membrane
Basement
membrane
Cytoplasm
Lamina lucida
Lamina densal
Reticular lamina
A
B
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