232
UNIT 3
Organ Systems
Figure 12-9B.
Proximal tubule.
EM,
3
4,606; inset
3
9,208
This is a cross section of a
proximal tubule
. It is lined by cuboidal and low columnar cells with apical
microvilli
, which form a
brush
border
, a feature that is associated with reabsorption function. The numerous
mitochondria
are more concentrated at the basolateral
surface where they support the energy requirements of sodium pumps located in the expanded plasmalemma. The apical regions of
the cells contain
pinocytotic vesicles
, which refl ect the uptake of proteins that evaded the F
ltration barrier in the renal corpuscle and
entered the F ltrate. The
inset
shows long microvilli and pinocytotic vesicles in the apical surface of the cells.
Basement
Basement
membrane
membrane
Basement
membrane
Brush border
Brush border
with glycocalyx
with glycocalyx
Brush border
with glycocalyx
Nuclei of the
Nuclei of the
cuboidal cells
cuboidal cells
Nuclei of the
cuboidal cells
Lumen
Lumen
Lumen
A
Pinocytotic
Pinocytotic
vescle
vescle
Pinocytotic
vesicle
Mitochondria
Mitochondria
Mitochondria
Microvilli
Microvilli
Microvilli
Nucleus
Nucleus
Nucleus
Lysosome
Lysosome
Lysosome
Pinocytotic
Pinocytotic
vesicles
vesicles
Pinocytotic
vesicles
Basement
Basement
membrane
membrane
Basement
membrane
Microvilli
Microvilli
Microvilli
Lysosome
Lysosome
Mitochondria
Lumen
Lumen
Lumen
B
Figure 12-9A.
Proximal tubules, renal cortex.
H&E,
3
754
Both
proximal convoluted
and
straight tubules
have a
similar structure and function. They are lined by large
acidophilic cuboidal cells
with
brush borders
formed
by numerous
long microvilli
. The brush border extends
into the
lumen
, which, in conjunction with postmortem
changes, makes the lumen appear smaller and F
lled with
acidophilic material (
brush border
and
glycocalyx
). The
proximal tubules have a substantial reabsorption function.
About 65% of the water and sodium and more than 90%
of glucose, amino acids, and bicarbonate are reabsorbed
by the proximal convoluted tubules. The proximal convo-
luted tubules are located in the cortical labyrinth and are
connected to the renal corpuscle at the urinary pole. The
proximal straight tubules are part of the loop of Henle
(±ig. 12-8B).
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