C h a p t e r 2 7
Disorders of the Bladder and Lower Urinary Tract
659
that selectively target bladder structures while minimiz-
ing undesired side effects.
Although sympathetic innervation is not essential to
the act of micturition, it allows the bladder to store a
large volume without the involuntary escape of urine—
a mechanism that is consistent with the fight-or-flight
function of the sympathetic nervous system. The blad-
der is supplied with
α
1
- and
β
2
-adrenergic receptors.
The
β
2
-adrenergic receptors are found in the detrusor
muscle. They produce relaxation of the detrusor mus-
cle, increasing the bladder volume at which the micturi-
tion reflex is triggered. The
α
1
-adrenergic receptors are
found in the trigone area, including the intramural ure-
teral musculature, bladder neck, and internal sphincter.
The activation of
α
1
-adrenergic receptors produces con-
traction of these muscles. Sympathetic activity ceases
when the micturition reflex is activated. During male
ejaculation, which is mediated by the sympathetic ner-
vous system, the musculature of the trigone area and
that of the bladder neck and prostatic urethra contract
and prevent the backflow of seminal fluid into the
bladder.
Because of their effects on bladder function, drugs
that selectively activate or block ANS outflow or
receptor activity can alter urine elimination. Table 27-1
describes the action of drug groups that impair bladder
function or can be used in the treatment of micturition
disorders. For example, many of the nonprescription
cold preparations contain
α
-adrenergic agonists and
antihistamine agents that have anticholinergic proper-
ties. These drugs can cause urinary retention. Many of
the antidepressant and antipsychotic drugs also have
anticholinergic actions that influence urination.
Evaluation of Bladder Function
Bladder function can be assessed by a number of meth-
ods.
8,9
Reports or observations of frequency, hesitancy,
straining to urinate, and a weak or interrupted urine
Bladder emptying
Cortical facilitation
Coordination of micturition
motor function
Inhibition of
somatic
neurons
Stimulation of
parasympathetic
neurons
Relaxation of
external
sphincter
Contraction of
detrusor muscle
Pudendal
nerve
External
sphincter
and pelvic
muscles
Bladder
Pelvic
nerve
Sacral cord
(S1-S3)
Detrusor
muscle
Pontine
micturition
center
Cerebral
cortex
Urine storage
Cortical inhibition
Coordination of bladder
storage functions
Stimulation of
sympathetic
neurons
Stimulation of
somatic
neurons
Relaxation of
detrusor
muscle
Contraction of
external
sphincter
Thoracolumbar
cord (T11-L2)
FIGURE 27-3.
Pathways and central nervous system centers involved in the control of bladder
emptying (left) and storage (right) functions. Efferent pathways for micturition (left) and urine storage
(right) also are shown.
