Editing Functional: Urinary Incontinence (section)

== Physiology of Urinary Continence ==

* '''Urinary continence is maintained during elevations in abdominal pressure by'''
*# '''Passive transmission of abdominal pressure to the proximal urethra presses the anterior wall against the posterior wall'''
*# '''A “guarding” reflex involving an active contraction of striated muscle of the external urinary sphincter can transiently help continence'''
*'''Male Sphincteric Mechanisms'''
** '''Internal sphincter'''
***'''Extends from the bladder neck to the distal verumontanum''' 
***'''Contributes to continence'''
** '''External sphincter'''
***'''Loss of external sphincter function, such as with traumatic pelvic injury, may not result in incontinence in men with an intact bladder neck. This is in contradistinction to the bladder neck in women, which is relatively weak, making women more vulnerable to incontinence with any deficiency of external sphincter function'''.
* '''Female Sphincteric Mechanisms'''
** Female urethra 
***Composed of four layers, with the middle muscular layer maintaining the resting urethral closure mechanism and the outer seromuscular layer augmenting this closing pressure. 
**The levator ani, urethropelvic ligament, and pubocervical fascia provide support to the bladder neck and underside of the bladder. The round ligament provides support to the uterus.
** '''Unlike the powerful continence zone created at the level of the bladder neck in men, continence in women is largely a result of the bulk of the muscle along the proximal urethra and/or midurethra responsible for sphincteric control.'''
*** Muscular forces (primarily striated muscle) create a nearly complete circumferential compression of the midurethra under the influence of tonic pudendal innervation.
** Fixation of the urethra by ligamentous support (pubourethral ligaments) normally minimizes movement of the proximal urethra, further contributing to continence by helping to prevent abdominal forces to be transmitted to the remainder of the urethra.
** '''It is the combined effect of these extraurethral forces, intrinsic urethral properties, and muscular elements that promotes continence, and loss of any one, or several in most cases, can result in UI in women.'''