Editing Pediatrics: Vesicoureteral Reflux (section)

== Functional Anatomy of the Antireflux Mechanism ==

* '''Normal physiologic factors that prevent reflux (3):'''
*# '''Functional integrity of the ureter'''
*#* '''Ureter represents a dynamic conduit'''
*# '''Anatomic design of the UVJ'''
*#* At the extravesical bladder hiatus, the 3 muscle layers of the ureter separate.
*#** '''The outer ureteral muscle merges with the outer detrusor muscle to form the Waldeyer sheath,''' which contributes to formation of the deep trigone.
*#** Intravesically, the inner muscle of the ureter merges with detrusor muscle to contribute to the superficial trigone. Some of these '''inner ureteral fibers pass medially to contribute to the intraureteric ridge (Mercier bar).'''
*#* '''The intramural ureter remains passively compressed by the bladder wall during bladder filling, preventing urine from entering the ureter'''.
*#** Adequate intramural length and fixation of the ureter between its extravesical and intravesical points is required to create this antirefluxing compression valve.
*#** '''Ratio of tunnel length to ureteral diameter found in normal children without reflux is ≈5:1 compared with a 1.4:1 ratio in refluxing UVJs'''
*# '''Functional dynamics of the bladder'''
** '''It is likely that in addition to architectural deficiencies of tunnel length, abnormalities in uterovesical smooth muscle and extracellular matrix composition and neural function may contribute to reflux'''
* Opening of the UVJ is achieved by active contraction of the longitudinal muscles within the tunnel. Closure of the UVJ results both from compression of the intramural ureter and a return to its full tunnel length as the ureteral muscle relaxes.