HUMAN BIOLOGY

the UrInary SyStem 227

(glow-mare-you-luss; plural: glom-
eruli). The cuplike wall region,
called the Bowman’s (glomer ular)
capsule, receives the substances
filtered from blood. The rest of the
nephron is a winding tubule (“little
tube”). Filtrate flows from the cup
into the proximal tubule (proxi-
mal means “next to”), then through
a hairpin-shaped loop of Henle
and into the distal tubule (“most
distant” from Bowman’s capsule). This part of the nephron
tubule empties into a collecting duct.

special vessels transport blood to, in,
and away from nephrons

Each hour, about 75 gallons of blood course through
your kidneys, delivered by the renal arteries. An afferent
arteriole brings blood to each nephron (afferent m e a n s “c a r-
rying toward”). The blood flows into the glomerulus inside
Bowman’s capsule. These capillaries are not like capillaries
in other parts of the body. Specialized pores between the
cells of their walls make them much more permeable than
other capillaries. Thus it is much easier for water and sol-
utes to move across the wall.

What do kidney nephrons do?

• Kidney nephrons filter water and solutes from blood. A cluster of
  capillaries called a glomerulus is the nephron’s blood-filtering unit.


• The capillaries in a glomerulus have pores in their walls that
  make the vessels unusually permeable.


• Arterioles transport blood to and from nephrons. Peritubular
  capillaries weave around nephron tubules and deliver filtered
  blood back to the general circulation.

taKe-Home message

Bowman’s capsule The

cuplike region of a nephron

that receives water and sol-

utes filtered from blood.

distal tubule The part of

the nephron tubule far-

thest from the Bowman’s

capsule.

loop of Henle The hairpin-

shaped midsection of a

nephron’s tubule.

peritubular capillaries

The set of capillaries that

weave around a nephron’s

tubules.

proximal tubule The por-

tion of the nephron tubule

closest to the Bowman’s

capsule.

Glomerular capillaries don’t

channel blood to venules, as other

capillaries do (Section 7.7). Instead,

they merge to form an efferent (“c a r-

rying away from”) arteriole. This

arteriole branches into peritubular

(“around the tubule”) capillaries.

As you can see in Figure 12.4B,

the peri tubular capillaries weave

around a nephron’s tubules. They

merge into venules, which carry fil-

tered blood out of the kidneys.

Figure 12.4 Animated! interacting with two sets of capillaries, nephrons are a kidney’s blood-filtering units.

a Diagram of a nephron. B The arterioles and capillaries associated with a nephron. (© Cengage Learning)

a Bowman’s capsule and tubular regions of

one nephron, cutaway view B^ Blood vessels associated with the nephron

proximal

tubule

(orange)

Bowman’s

capsule

(red)

loop of Henle

(yellow)

distal

tubule

(brown)

collecting

tubule (tan)

renal

cortex

renal

medulla

efferent arteriole

glomerulus

afferent arteriole

peritubular

capillaries

renal

artery

renal

vein

MicroScan/Phototake
Colored microscope
image of a glomerulus

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