34
UNIT 2
Basic Tissues
Figure 3-6A.
Simple
cuboidal
epithelium,
tubules of kidney.
H&E,
3
155; inset
3
410
The appearance of this epithelium varies in
different
segments of the uriniferous tubules. For example,
in the proximal tubules, the cuboidal cells have
pink-stained cytoplasm and display numerous
long
microvilli
on the apical surface. The microvilli
generally ± ll the lumen and may appear disrupted
in histological specimens, but this is an artifact of
postmortem deterioration. The acidophilia of the
cytoplasm of
proximal tubule cells
results partly
from the numerous mitochondria that provide the
ATP necessary to power the ion pumps in the baso-
lateral membranes of these cells. The
cuboidal cells
of distal tubules have short and scanty microvilli.
They display less acidophilia than the proximal
tubules, although they do have mitochondria that
support ion pumps. The cuboidal cells forming
collecting tubules
and
ducts
have few microvilli,
and the cytoplasm is less stained. A defect in renal
tubules can result in renal tubular
acidosis
(acido-
sis and electrolyte disturbance). (L, lumen.)
Simple
Simple
cuboidal
cuboidal
epithelium
epithelium
Simple
cuboidal
epithelium
Proximal tubule
Proximal tubule
Proximal tubule
Collecting duct
Collecting duct
Simple cuboidal
Simple cuboidal
epithelium
epithelium
Simple cuboidal
epithelium
Collecting duct
Simple cuboidal
Simple cuboidal
epithelium
epithelium
Simple cuboidal
epithelium
L
L
L
L
A
D. Cui
Microvilli
Cuboidal cell
Basement membrane
Connective tissue
B
Figure 3-6B.
A representation of simple
cuboidal epithelium of the proximal tubule in the
kidney.
These simple
cuboidal epithelial cells
have round
nuclei that are in the center of the cells. The api-
cal surface of the cell exhibits abundant long
microvilli
, indicating absorption and secretion
functions. Most of the water, sodium, chloride,
amino acids, proteins, and glucose in the glom-
erular ±
ltrate are reabsorbed by the cuboidal cells
of the proximal tubules and transported into the
underlying
connective tissue
.
CLINICAL CORRELATION
Figure 3-6C.
Renal Fanconi Syndrome.
Renal Fanconi syndrome
is mainly an impairment of prox-
imal tubular function in the kidney resulting from an abnor-
mality in the epithelial lining. The alteration of the epithe-
lium can be caused by a variety of genetic defects (mostly in
children) and by certain environmental factors. The result
is that some substances that should be reabsorbed into the
bloodstream are instead excreted in the urine. These sub-
stances include glucose, amino acids, phosphate, bicarbon-
ate, and calcium. Their loss into the urine may lead to fail-
ure to thrive in children and decreased bone mineralization
(
rickets
in children,
osteomalacia
in adults).
Some histological features typical of renal Fanconi
syndrome are illustrated here. Epithelial cells become
more
squamous
rather than cuboidal,
nuclei
are
distorted
,
the
basement membrane
becomes
wrinkled
and
thickened
,
and
microvilli
are
reduced
in number and length.
D. Cui
Loss of microvilli
Thickened/wrinkled
basement membrane
Distorted nucleus of cuboidal cell
Connective tissue
Distorted squamous cell
Enlarged
cuboidal cell
C
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