958
UNIT 4
Maintenance of the Body
25
Each nephron consists of a
renal corpuscle
and a
renal tubule
.
All of the renal corpuscles are located in the renal cortex, while
the renal tubules begin in the cortex and then pass into the me-
dulla before returning to the cortex.
Renal Corpuscle
Each
renal corpuscle
consists of a tuF of capillaries called a
glomerulus
(glo-mer
9
u-lus;
glom
5
ball of yarn) and a cup-
shaped hollow structure called the
glomerular capsule
(or
Bowman’s capsule
). Te glomerular capsule completely sur-
rounds the glomerulus, much as a well-worn baseball glove en-
closes a ball, and is continuous with its renal tubule.
Glomerulus
Te endothelium of the glomerular capillaries is
fen-
estrated
(penetrated by many pores), which makes these capillar-
ies exceptionally porous. Tis property allows large amounts of
solute-rich but virtually protein-free fluid to pass from the blood
into the glomerular capsule. Tis plasma-derived fluid or
filtrate
is the raw material that the renal tubules process to form urine.
Glomerular Capsule
Te glomerular capsule has an external
parietal layer and a visceral layer that clings to the glomerular
capillaries.
Te
parietal layer
is simple squamous epithelium (±igures 25.5,
25.8, and 25.10a). Tis layer contributes to the capsule structure
but plays no part in forming filtrate.
artery to reach the kidney. Tese sympathetic vasomotor fibers
regulate renal blood flow by adjusting the diameter of renal arte-
rioles and also influence the formation of urine by the nephron.
Check Your Understanding
1.
Roger is hit in the lower back by an errant baseball. What
protects his kidneys from this mechanical trauma?
2.
From inside to outside, list the three layers of supportive
tissue that surround each kidney. Where is the parietal
peritoneum in relation to these layers?
3.
The lumen of the ureter is continuous with a space inside the
kidney. This space has branching extensions. What are the
names of this space and its extensions?
For answers, see Appendix H.
Nephrons
Describe the anatomy of a nephron.
Nephrons
(nef
9
ronz) are the structural and functional units of
the kidneys. Each kidney contains over 1 million of these tiny
blood-processing units, which carry out the processes that form
urine
(Figure 25.5)
. In addition, there are thousands of
collect-
ing ducts
, each of which collects fluid from several nephrons
and conveys it to the renal pelvis.
Cortical radiate
vein
Cortical radiate
artery
Arcuate vein
Arcuate artery
Interlobar vein
Interlobar artery
Segmental arteries
Renal artery
Renal vein
Renal pelvis
Ureter
Renal medulla
Renal cortex
(a) Frontal section illustrating major blood vessels
Aorta
Renal artery
Segmental artery
Interlobar artery
Arcuate artery
Cortical radiate artery
Afferent arteriole
Glomerulus (capillaries)
Nephron-associated blood vessels
(see Figure 25.7)
Inferior vena cava
Renal vein
Interlobar vein
Arcuate vein
Cortical radiate vein
Peritubular capillaries
or vasa recta
Efferent arteriole
(b) Path of blood flow through renal blood vessels
Figure 25.4
Blood vessels of the kidney.
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