Editing Functional: Neural Control of Storage and Voiding (section)

== Lower urinary tract anatomy ==

=== Bladder ===
* '''Layers:'''
** '''Urothelium'''
*** ≈7 cells thick
*** '''Functions of the urothelium (4):'''
***# '''Relatively impermeable barrier (primary role)''' to protect the underlying stroma of the bladder
***#* Uroplakin and TJ proteins play key parts in urothelial barrier function
***# '''Sentinel defense against uropathogenic bacterial infections'''
***#* Uroplakins have also been shown to act as the primary attachment site of type 1 piliated uropathogenic E. Coli.
***# '''Afferent signaling;''' urothelial cells can release and respond to neurotransmitters
***#* Myofibroblasts mediate interaction between urothelial cells and afferent nerves
***# '''Modulation of detrusor smooth muscle contractility'''
*** '''The glycosaminoglycan (GAG) layer may have importance in bacterial anti-adherence, but''' '''there is no definite evidence that the GAG layer serves an impermeability function'''
** '''Lamina propria'''
*** Contains a diffuse plexus of unmyelinated nerve fibers, interstitial cells (myofibroblasts) and microvasculature
** '''Detrusor'''
*** In the bladder body, myofibrils are arranged into fascicles (bundles) in random directions
*** It is unlikely that every smooth muscle cell receives direct synaptic contact; the presence of '''gap junctions allows excitation to propagate throughout the smooth muscle''' syncytium
*** '''Detrusor smooth muscle has afferent innervation''' that could mediate afferent signals related to smooth muscle activity
*** '''The detrusor contractile ability rapidly declines''' if it is deprived of oxygen or a metabolic substrate, as would occur '''in ischemia'''

=== Internal (smooth) sphincter ===
* '''<span style="color:#ff0000">A complete and competent ring of smooth muscle and at the bladder neck in males; not found in females</span>'''
* '''<span style="color:#ff0000">A physiologic but not an anatomic sphincter</span>'''
* '''<span style="color:#ff0000">Not under voluntary control</span>'''

=== External urinary (striated) sphincter (EUS) ===
* '''Striated muscles are characterized as slow vs. fast-twitch'''
** '''Slow-twitch fibers: suitable for maintaining sphincter tone for prolonged periods'''
** '''Fast-twitch fibers: may be needed to add to sphincter tone rapidly (i.e. to maintain continence when intra-abdominal pressure is abruptly increased)'''
* '''Composed of 2 parts:'''
*# '''Periurethral striated muscle of the pelvic floor'''
*#* Closely surrounds the urethra at the level of the membranous portion in males and primarily the middle segment in females
*#* '''Contains both fast-twitch and slow-twitch fibers'''
*#** '''Hypothesized that pelvic floor exercises or electrostimulation improve continence in SUI by causing by the conversion of fast-twitch to slow-twitch striated muscle fibers'''
*# '''Striated muscle that is a part of the outer wall of the proximal urethra in males and females (also known as rhabdosphincter)'''
*#* '''Contains predominantly slow-twitch fibers'''
* '''In males,'''
** '''Covers the ventral surface of the prostate as a crescent shape proximal to the verumontanum'''
** '''Then assumes a horseshoe shape distal to the verumontanum'''
** '''Then as a crescent shape at the bulbar urethra'''
* '''In females,'''
** '''Covers the ventral surface of the urethra in a horseshoe shape'''
* '''<span style="color:#ff0000">Under voluntary control</span>'''
* '''<span style="color:#ff0000">Innervation: pudendal nerve (S2-S4)</span>'''
* '''In addition to striated muscle, the EUS contains smooth muscle which receives sympathetic (noradrenergic) innervation'''[https://www.auanet.org/guidelines/urethral-stricture-guideline §]