800
UNIT FIVE
The urgent need to urinate and the burning pain of urination may
signal inflammation or infection of the bladder and/or ureters.
Inflammation of the bladder (cystitis) is more common in women
because the urethral pathway is shorter than in men. InF
ammation of
the ureters is called ureteritis.
In a urinary tract infection (UTI), bacteria ascend from the blad-
der to the ureters on the continuous linings. Urination is frequent,
painful, scant, and may be bloody, with accompanying abdominal
pain. Usually pathogenic bacteria in the urinary tract remain outside
the cells and are easily killed with antibiotic drugs or prevented from
attaching to ureter lining cells by exposure to compounds in cranberry
and blueberry juices that the person drinks. However, certain bacteria,
such as
Escherichia coli,
enter the lining cells, forming “intracellular bac-
terial communities.” The microbes can emerge and start new infections,
explaining why some people experience frequent UTIs.
PRACTICE
30
Describe the trigone of the urinary bladder.
31
Describe the structure of the bladder wall.
32
What type of nerve ±
bers supply the detrusor muscle?
Urethra
The
urethra
is a tube that conveys urine from the urinary
bladder to the outside of the body. Its wall is lined with
mucous membrane and has a thick layer of longitudinal
smooth muscle fibers. The urethral wall also has many
urethra. The trigone generally remains in a F
xed position,
even though the rest of the bladder distends and contracts.
The wall of the urinary bladder consists of four layers.
The inner layer, or
mucous coat,
includes several thicknesses
of transitional epithelial cells similar to those lining the ure-
ters and the upper portion of the urethra. The thickness of
this tissue changes as the bladder expands and contracts.
During distension, the tissue appears to be only two or three
cells thick, but during contraction, it appears to be F
ve or six
cells thick (see F
g. 5.9).
The second layer of the bladder wall is the
submucous
coat.
It consists of connective tissue and has many elastic
F bers.
The third layer of the bladder wall, the
muscular coat,
is primarily composed of coarse bundles of smooth muscle
F bers. These bundles are interlaced in all directions and at
all depths, and together they comprise the
detrusor muscle
(de-truz
or mus
l). The portion of the detrusor muscle that
surrounds the neck of the bladder forms an
internal urethral
sphincter.
Sustained contraction of this sphincter muscle pre-
vents the bladder from emptying until the pressure within it
increases to a certain level. The detrusor muscle has para-
sympathetic nerve fibers that function in the reflex that
passes urine.
The outer layer of the wall, the
serous coat,
consists of
the parietal peritoneum. It is found only on the upper sur-
face of the bladder. Elsewhere, the outer coat is composed
of fibrous connective tissue
(fig. 20.30)
. ±rom Science to
Technology 5.2 on page 166 discusses a tissue-engineered
replacement bladder.
(a)
(b)
Detrusor
muscle
Submucous
coat
Mucous coat
Trigone
Internal urethral sphincter
Neck
Prostate gland
Urethra
Region of external
urethral sphincter
Openings of
the ureters
Serous coat
Urinary bladder
Ureter
Ureter
Ductus (vas)
deferens
Seminal
vesicle
Prostate gland
Urethra
FIGURE 20.29
A male urinary bladder. (
a
) Longitudinal section. (
b
) Posterior view.
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