Chapter 25
The Urinary System
955
25
An adult’s kidney has a mass of about 150 g (5 ounces) and its
average dimensions are 11 cm long, 6 cm wide, and 3 cm thick—
about the size of a large bar of soap. Te lateral surface is convex.
Te medial surface is concave and has a vertical cleF called the
renal
hilum
that leads into an internal space within the kidney
called the
renal sinus
. Te ureter, renal blood vessels, lymphatics,
and nerves all join each kidney at the hilum and occupy the sinus.
Atop each kidney is an
adrenal
(or
suprarenal
)
gland
, an endo-
crine gland that is functionally unrelated to the kidney.
Tree layers of supportive tissue surround each kidney (±ig-
ure 25.2a). ±rom superficial to deep, these are:
Te
renal fascia
, an outer layer of dense fibrous connective
tissue that anchors the kidney and the adrenal gland to sur-
rounding structures
Te
perirenal fat capsule
, a fatty mass that surrounds the
kidney and cushions it against blows
Te
fibrous capsule
, a transparent capsule that prevents in-
fections in surrounding regions from spreading to the kidney
Homeostatic Imbalance
25.1
Te kidneys’ fatty encasement holds them in their normal body
position. If the amount of fatty tissue dwindles (as with extreme
emaciation or rapid weight loss), one or both kidneys may
drop to a lower position, an event called
renal ptosis
(to
9
sis; “a
fall”). Renal ptosis may cause a ureter to become kinked, caus-
ing urine to back up and exert pressure on kidney tissue. Backup
of urine from ureteral obstruction or other causes is called
Producing
erythropoietin
and
renin
(re
9
nin;
ren
5
kidney),
important molecules for regulating red blood cell produc-
tion and blood pressure, respectively.
Converting vitamin D to its active form.
Carrying out gluconeogenesis during prolonged fasting (see
p. 924).
Te urine-forming kidneys are crucial components of
the
urinary system
(Figure 25.1)
. Te urinary system also
includes:
Ureters
—paired tubes that transport urine from the kidneys
to the urinary bladder
Urinary bladder
—a temporary storage reservoir for urine
Urethra
—a tube that carries urine from the bladder to the
body exterior
Kidney Anatomy
Describe the gross anatomy of the kidney and its coverings.
Location and External Anatomy
Te bean-shaped kidneys lie in a retroperitoneal position (be-
tween the dorsal body wall and the parietal peritoneum) in
the
superior
lumbar region
(Figure 25.2)
. Extending approxi-
mately from ²
12
to L
3
, the kidneys receive some protection from
the lower part of the rib cage (±igure 25.2b). Te right kidney is
crowded by the liver and lies slightly lower than the leF.
Esophagus (cut)
Inferior vena cava
Adrenal gland
Hepatic veins (cut)
Renal artery
Renal hilum
Renal vein
Iliac crest
Kidney
Ureter
Urinary
bladder
Urethra
Aorta
Rectum (cut)
Uterus (part of female
reproductive system)
Figure 25.1
The urinary system.
Anterior view of the female urinary organs. (Most
unrelated abdominal organs have been omitted.)
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