Porth's Essentials of Pathophysiology, 4e

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Disorders of the Bladder and Lower Urinary Tract

C h a p t e r 2 7

Urine storage

Bladder emptying

Cortical inhibition

Cortical facilitation

Cerebral cortex

Coordination of bladder storage functions

Coordination of micturition motor function

Pontine micturition center

Thoracolumbar cord (T11-L2)

Stimulation of sympathetic neurons

Stimulation of somatic neurons

Inhibition of somatic neurons

Stimulation of parasympathetic neurons

Sacral cord (S1-S3)

Pelvic nerve

Detrusor muscle

Pudendal nerve

Bladder

Relaxation of detrusor muscle

Contraction of external sphincter

Relaxation of external sphincter

Contraction of detrusor muscle

External sphincter and pelvic muscles

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.

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