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Under normal circumstances, the ureterovesical junction allows urine to enter the bladder but prevents urine from regurgitating into the ureter, particularly at the time of voiding. In this way, the kidney is protected from high pressure in the bladder and from contamination by infected vesical urine. When this valve is incompetent, the chance for development of urinary infection is significantly enhanced, and pyelonephritis may occur.
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ANATOMY OF THE URETEROVESICAL JUNCTION
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An understanding of the causes of vesicoureteral reflux (VUR) requires knowledge of the anatomy of the ureterovesical junction. Anatomic studies performed by Hutch (1972) and Tanagho and Pugh (1963) (Figure 13–1) are incorporated into the following discussion.
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Mesodermal Components
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The mesodermal component, which arises from the Wolffian duct, is made up of two parts that are innervated by the sympathetic nervous system.
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A. The Ureter and the Superficial Trigone
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The smooth musculature of the renal calyces, pelvis, and extravesical ureter is composed of helically oriented fibers that allow for peristaltic activity. As these fibers approach the vesical wall, they are reoriented into the longitudinal plane. The ureter passes obliquely through the vesical wall; the intravesical ureteral segment is thus composed of longitudinal muscle fibers only and therefore cannot undergo peristalsis. As these smooth-muscle fibers approach the ureteral orifice, those that form the roof of the ureter swing to either side to join those that form its floor. They then spread out and join equivalent muscle bundles from the other ureter and continue caudally, thus forming the superficial trigone. The trigone passes over the neck of the bladder, ending at the verumontanum in the male and just inside the external urethral meatus in the female. Thus, the ureterotrigonal complex is one structure. Above the ureteral orifice, it is tubular; below that point, it is flat.
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B. Waldeyer’s Sheath and the Deep Trigone
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Beginning at a point about 2–3 cm above the bladder, an external layer of longitudinal smooth muscle surrounds the ureter. This muscular sheath passes through the vesical wall, to which it is connected by a few detrusor fibers. As it enters the vesical lumen, its roof ...