The Urinary System
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
that leads into an internal space within the kidney
. Te ureter, renal blood vessels, lymphatics,
and nerves all join each kidney at the hilum and occupy the sinus.
Atop each kidney is an
, 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:
, an outer layer of dense ﬁbrous connective
tissue that anchors the kidney and the adrenal gland to sur-
perirenal fat capsule
, a fatty mass that surrounds the
kidney and cushions it against blows
, a transparent capsule that prevents in-
fections in surrounding regions from spreading to the kidney
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
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
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
Te urine-forming kidneys are crucial components of
. Te urinary system also
—paired tubes that transport urine from the kidneys
to the urinary bladder
—a temporary storage reservoir for urine
—a tube that carries urine from the bladder to the
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
. Extending approxi-
mately from ²
, 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.
Inferior vena cava
Hepatic veins (cut)
Uterus (part of female
The urinary system.
Anterior view of the female urinary organs. (Most
unrelated abdominal organs have been omitted.)