Maintenance of the Body
arterioles, they only experience low pressure. As a result, these
low-pressure, porous capillaries readily absorb solutes and
water from the tubule cells as these substances are reclaimed
from the ﬁltrate. Renal tubules are closely packed together, so
the peritubular capillaries of each nephron absorb substances
from several adjacent nephrons.
Notice in Figure 25.7a that the eﬀerent arterioles
serving the juxtamedullary nephrons tend
to break up into
meandering peritubular capillaries. Instead they form bun-
dles of long straight vessels called
“straight vessels”) that extend deep into the medulla paralleling
the longest nephron loops. Te thin-walled vasa recta play an
important role in forming concentrated urine, as we will de-
In summary, the nephrons have two functionally diﬀerent
capillary beds separated by eﬀerent arterioles. Te ﬁrst capil-
lary bed (the glomerulus) produces the ﬁltrate. Te second (a
combination of peritubular capillaries and vasa recta) reclaims
most of that ﬁltrate.
Juxtaglomerular Complex (JGC)
Each nephron has a
juxtaglomerular complex (JGC)
u-lar), a region where the most distal portion of
the ascending limb of the nephron loop lies against the aﬀerent
arteriole feeding the glomerulus (and sometimes the eﬀerent
. Both the ascending limb and the aﬀer-
ent arteriole are modiﬁed at the point of contact.
nate close to (
near to) the cortex-medulla junction,
and they play an important role in the kidneys’ ability to pro-
duce concentrated urine. Tey have long nephron loops that
deeply invade the medulla, and their ascending limbs have
both thin and thick segments.
Nephron Capillary Beds
Te renal tubule of every nephron is closely associated with two
capillary beds: the
(Figure 25.7). In addition, juxtamedullary nephrons are associ-
ated with special capillaries called the
Te glomerulus, in which the capillaries run in
parallel, is specialized for ﬁltration. It diﬀers from all other
capillary beds in the body in that it is both fed and drained
spectively. Tis arrangement maintains the high pressure in the
glomerulus that is needed for ﬁltration, a process we discuss on
p. 965. Filtration produces a large amount of ﬂuid, most (99%)
of which is reabsorbed by the renal tubule cells and returned to
the blood in the peritubular capillary beds.
Te aﬀerent arterioles arise from the
cortical radiate arteries
that run through the renal cortex. Te eﬀerent arterioles feed
into either the peritubular capillaries or the vasa recta.
closely to adjacent renal tubules and empty into nearby
venules. Because they arise from the high-resistance eﬀerent
Red blood cell
Podocyte cell body
• Macula densa cells
of the ascending limb
of nephron loop
• Granular cells
Juxtaglomerular complex (JGC) of a nephron.
Mesangial cells that surround
the glomerular capillaries (glomerular mesangial cells) are not part of the JGC.