To understand vesicoureteral (ves-ih-ko-yu-ree-ter-ul) reflux, one needs to understand the normal structure and function of the urinary tract.
The Urinary System
The kidneys clean and filter blood to produce urine. Urine is liquid waste. Urine travels from the kidneys down the ureters and into the bladder. The bladder holds the urine and acts as a storage tank. As the bladder fills, the wall of the bladder relaxes to hold more urine. The control muscle (sphincter) remains tight to prevent leakage of urine. Once in the bladder, the urine is stopped from going back into the ureters by a valve mechanism. When the bladder gets full, it sends a message to the brain. The brain decides when urination should start. The bladder contracts while the sphincter muscle relaxes allowing the bladder to squeeze all of the urine out.