The external urethral sphincter, innervated by the somatic nervous system, allows for the voluntary control of urination. As the bladder fills, signals are sent to the cortical center of the brain, creating the urge to urinate. Urination begins when the cortical center of the brain triggers inhibition of sympathetic impulses and stimulates the parasympathetic system, so that the internal and external sphincters relax and the detrusor muscle of the bladder contracts. Aging causes a number of changes in urinary tract physiology, all of which can affect continence. Decreased strength of pelvic support muscles Atrophic changes in urethral lining and bladder trigone in postmenopausal women 2 a Adapted from reference 2.
Urinary incontinence is especially prevalent in women.
This is due in part to the presence of estrogen receptors throughout the urethra and bladder. In postmenopausal women, estrogen deficiency causes atrophy of the urethral epithelium, resulting in decreased efficiency of the urethral sphincters. Stress Incontinence Stress incontinence is caused by the inability of the internal urethral sphincter to remain closed in response to increased intra-abdominal pressures such as those that occur with coughing or sneezing. Alpha-adrenergic agonists, such as phenylpropanolamine and pseudoephedrine, may also prove useful in increasing muscle tone in the bladder and urethra. Conversely, stress incontinence may be exacerbated in patients taking alpha-adrenergic blockers.