24
UNIT 1
Basic Principles of Cell Structure and Function
Figure 2-11A.
Ion-pumping cells, renal tubule.
EM,
3
9,060
Nucleus
Mitochondria
Basal lamina of
renal tubule cell
Red blood cell
in capillary
Interstitial
compartment
Basolateral folds
of renal tubule
epithelial cell
A
Striations
Striations
Striations
Proximal tubule cells
Proximal tubule cells
with basolateral folds,
with basolateral folds,
ion pumps, and abundant
ion pumps, and abundant
mitochondria
mitochondria
Proximal tubule cells
with basolateral folds,
ion pumps, and abundant
mitochondria
Collecting duct
Collecting duct
cells with channels,
cells with channels,
but without ion pumps
but without ion pumps
Collecting duct
cells with channels,
but without ion pumps
Striated duct
Renal medulla
B
Examples of
epithelial
cells
that function primarily to
move
ions
from a lumen to the
interstitial compartment
form the walls of
some
renal tubules
and of some
ducts
of
salivary
glands
. Perhaps surprisingly, the molecular pumps are located not in the apical
cell membrane but rather in the
plasmalemma
of the basal and lateral surfaces of the cells. These
ATP
-
requiring
pumps transfer
sodium
ions
from the cytosol of the cell into the interstitial compartment. Sodium ions are pulled from the lumen at the apex of the
cell by the gradient created by the basolateral pumps. The surface area of the membrane containing the pumps is greatly increased
by numerous, deep
basolateral folds
. The energy required to pump ions against a concentration gradient is supplied by numerous
mitochondria
packed into the cytoplasm of the basolateral folds.
Figure 2-11B.
Light microscopic appearance of
ion-pumping cells.
H&E,
3
770 main panel;
3
710
inset
Light microscopic views of
cells that pump ions
from
one compartment to another are consistent with the
ultrastructural features of these cells. The
cytoplasm
is
distinctly
acidophilic
(
eosinophilic
in an H&E-stained
specimen) owing to the abundance of
mitochondria
,
particularly in the basal portions of the cells. In paraf-
F n sections such as the
main panel
view of the renal
medulla, the
basolateral folds
are usually difF cult to
discern. The
inset
shows a plastic-embedded, 1-
μ
m
thick section of a duct from a
submandibular salivary
gland
. Evidence of the basolateral folds can be seen
here as vertical stripes in the basal cytoplasm of these
cells, which function to retrieve ions from the secre-
tion (saliva). This appearance is the basis of the term
striated duct
for this structure.
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