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CHAPTER TWENTY
Urinary System
Symphysis pubis
Prostate gland
Urinary bladder
Urethra
Ureter
Rectum
Parietal peritoneum
Abdominal wall
Rectum
(a)
(b)
Kidney stones, usually composed of calcium oxalate, calcium phos-
phate, uric acid, or magnesium phosphate, can form in the renal pel-
vis. A stone passing into a ureter produces severe pain in the region of
the kidney and radiating into the abdomen, pelvis, and lower limbs.
Nausea and vomiting may also occur.
About 60% of kidney stones pass spontaneously; the others
must be removed. Shock waves applied from outside the body are
used to fragment kidney stones. This procedure, called
extracorpo-
real shock-wave lithotripsy
(ESWL), focuses high-energy shock waves
through water (either in a tub or in a water-F
lled sack placed against
the patient). The stones shatter into fragments small enough to be
eliminated with urine.
Urinary Bladder
The
urinary bladder
is a hollow, distensible, muscular
organ in the pelvic cavity, posterior to the symphysis pubis
and inferior to the parietal peritoneum (
f g. 20.28
and refer-
ence plate 8). In a female, the bladder contacts the anterior
walls of the uterus and vagina, and in a male, the bladder
lies posteriorly against the rectum.
The pressure of surrounding organs alters the spherical
shape of the bladder. When the bladder is empty, its inner
wall forms many folds, but as it F
lls with urine, the wall
becomes smoother. At the same time, the superior surface of
the bladder expands upward into a dome.
When greatly distended, the bladder pushes above the
pubic crest and into the region between the abdominal wall
and the parietal peritoneum. The dome can reach the level of
the umbilicus and press against the coils of the small intestine.
The internal fl oor of the bladder includes a triangular
area called the
trigone,
which has an opening at each of its
three angles
(f g. 20.29)
. Posteriorly, at the base of the tri-
gone, the openings are those of the ureters. Anteriorly, at the
apex of the trigone, is a short, funnel-shaped extension called
the
neck
of the bladder, which contains the opening into the
frequency keeps pace with the rate of urine formation. If urine
forms quickly, a peristaltic wave may pass every few seconds;
if it forms more slowly, a wave may pass every few minutes.
A peristaltic wave reaching the urinary bladder spurts
urine into it. A fl aplike fold of mucous membrane covers the
opening where the urine enters. This fold acts as a valve,
allowing urine to enter the bladder from the ureter but pre-
venting it from backing up from the bladder into the ureter.
If a ureter becomes obstructed, such as by a small kidney
stone (renal calculus) in its lumen, strong peristaltic waves
begin in the proximal part of the tube, which may help move
the stone into the bladder. The presence of a stone usually
also stimulates a sympathetic refl ex (ureterorenal refl
ex) that
constricts the renal arterioles and reduces urine production
in the affected kidney.
PRACTICE
26
Describe the structure of a ureter.
27
How is urine moved from the renal pelvis to the urinary bladder?
28
What prevents urine from backing up from the urinary bladder
into the ureters?
29
How does an obstruction in a ureter a±
ect urine production?
FIGURE 20.27
Cross section of a ureter (75×).
FIGURE 20.28
The urinary bladder is in the pelvic cavity and behind the symphysis pubis. (
a
) In a female, it contacts the uterus and
vagina. (
b
) In a male, it lies against the rectum.
Mucous coat
Lumen
Muscular coat
Fibrous coat
Adipose tissue
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