The Urinary Bladder Stores Urine
and Expels It from the Body
LEARNING OBJECTIVES
1.
Describe
the function of the ureters, urinary
bladder, and urethra.
2.
Compare
the structure of the urethra in males
and females.
3.
Explain
the process of micturition.
he fluid leaving the collecting ducts of the neph-
rons is now called urine. Urine passes from the
kidneys to the urinary bladder via the ureters
(Figure 15.7a). The ureters pass under the
urinary bladder for several centimeters, causing the bladder
to compress the ureters and thus precent backflow of urine
when pressure builds up in the urine during urination.
The Urinary Bladder Is a
Temporary Storage Area
The urinary bladder is a hollow muscular organ situated in
the pelvic cavity behind the pubic symphysis. In males, it is
directly in front of the rectum. In females, it is in front of
the vagina and below the uterus. Folds of the peritoneum
hold the urinary bladder in position.
The muscular layer of the urinary bladder consists of
three layers of smooth muscle called the detrusor muscle
(de-TROO-ser). The urinary bladder’s smooth muscle al-
T h e s t r u c t u r e s o f t h e u r e t e r s , u r i n a r y b l a d d e r , a n d u r e t h r a a n d t h e i r f u n c t i o n s
F i g u r e 1 5 . 7
a.
The ureters,
urinary
bladder, and
urethra
Ureteral openings
into the urinary bladder
Peritoneum
helps holds the urinary
bladder in place.
Internal
urethral
sphincter
is a
smooth muscle that opens and
closes the urethra involuntarily.
External
urethral
sphincter
is a skeletal
muscle that opens and closes voluntarily.
External
urethral
orifice
is
the opening of the urethra
to the outside.
When empty, the urinary bladder
looks like a deflated balloon. As it
fills, it becomes round and then
pear-shaped. The bladder holds an
average of 700-800 mL of urine.
Anterior
view
of frontal section
Ureters
transport urine from the
kidneys to the urinary bladder. The
ureters tunnel a short distance within
the urinary bladder wall. As the
urinary bladder fills, it expands and
compresses the ureters, thereby
preventing the backflow of urine.
Detrusor muscle
consists of
three layers of smooth
muscle that stretch when the
urinary bladder fills and
contract to push out urine.
Urethra
is a small tube that leads
from the urinary bladder
to the outside.
Rugae
in the mucosa of the urinary
bladder and the lining transitional
epithelium allow the urinary bladder
to expand as it fills.
450 CHAPTER 15
The Urinary System and Fluid, Electrolyte, and Acid-Base Balance
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