660
U N I T 7
Kidney and Urinary Tract Function
stream are suggestive of outflow obstruction. Palpation
and percussion provide information about bladder
distention.
Postvoid residual (PVR) urine volume provides
information about bladder emptying. It can be esti-
mated by abdominal palpation and percussion.
Catheterization and ultrasonography can be used to
obtain specific measurements of PVR. A PVR value of
less than 50 mL is considered adequate bladder empty-
ing, and more than 200 mL indicates inadequate blad-
der emptying.
8
Pelvic examination is used in women to assess peri-
neal skin condition, perivaginal muscle tone, genital
atrophy, pelvic prolapse (e.g., cystocele, rectocele, uter-
ine prolapse), pelvic mass, or other conditions that may
impair bladder function (see Chapter 40). Bimanual
examination (i.e., pelvic and abdominal palpation) can
be used to assess PVR volume. Rectal examination is
used to test for perineal sensation, sphincter tone, fecal
impaction, and rectal mass. It is used to assess the con-
tour of the prostate in men.
Urine tests provide information about kidney func-
tion and urinary tract infections. The presence of bacte-
riuria or pyuria suggests urinary tract infection and the
possibility of urinary tract obstruction.
9
Blood tests (i.e.,
blood urea nitrogen and creatinine) provide information
about renal function.
Bladder structures can be visualized indirectly by tak-
ing x-ray films of the abdomen and through excretory
urography, which involves the use of a radiopaque dye,
computed tomographic (CT) scanning, magnetic reso-
nance imaging (MRI), or ultrasonography. Urodynamic
studies are used to evaluate bladder function and void-
ing problems. Cystoscopy enables direct visualization of
the urethra, bladder, and ureteral orifices.
TABLE 27-1
Action of Drug Groups on Bladder Function
Function
Drug Groups
Mechanism of Action
Detrusor Muscle
Increased tone and contraction Cholinergic drugs
Stimulate parasympathetic receptors that cause
detrusor contraction
Inhibition of detrusor muscle
relaxation during filling
β
2
-Adrenergic blockers
Block
β
2
receptors that produce detrusor muscle
relaxation
Anticholinergic drugs and drugs with
an anticholinergic action
Block the muscarinic receptors that cause detrusor
muscle contraction
Decreased tone
Calcium channel blockers
May interfere with influx of calcium to support
contraction of detrusor smooth muscle
Internal Bladder Sphincter
Increased tone
α
1
-Adrenergic agonists
Activate
α
1
receptors that produce contraction of the
smooth muscle of the internal sphincter
Decreased tone
α
1
-Adrenergic blockers
Block contraction of the smooth muscle of the
internal sphincter
External Sphincter
Decreased tone
Skeletal muscle relaxants
Decrease the tone of the external sphincter by acting
at the level of the spinal cord or by interfering with
release of calcium in the muscle fibers
SUMMARY CONCEPTS
■■
Although the kidneys control the formation of
urine, its storage and periodic elimination depend
on the coordinated activity of the smooth and
striated muscle of the two functional units of the
lower urinary tract—the urinary bladder, which
serves as a storage reservoir; and the urethra and
urethral sphincter, which function as an outlet for
urine elimination.
■■
The bladder is composed of four layers: an
outer serosal layer, a smooth muscle layer
called the detrusor muscle, a submucosal layer
of connective and elastic tissue, and an inner
epithelial layer.The detrusor muscle is the
muscle of micturition or passage of urine.The
inner epithelial layer prevents substances in
the urine from moving into the bloodstream
and its mucin layer acts as defense against
infection.
■■
Normal bladder function requires interaction
between the sensory and motor components
of both the autonomic nervous system (ANS),
which controls the involuntary smooth muscle
activity of the detrusor muscle, and the somatic
nervous system, which controls voluntary skeletal
muscle activity of the external sphincter.These
functions are controlled by three ascending levels
of nervous system control: the spinal cord reflex
