Urine flows from each kidney through tubes called ureters and into the bladder. When the bladder is full, it squeezes and sends the urine out through the urethra. None of the urine should flow back into the ureter when the bladder is squeezing. Each ureter has a one-way valve where it enters the bladder that prevents urine from flowing back up the ureter.

But in some people, urine flows back up to the kidney. This is called vesicoureteral reflux.

Over time, the kidneys may be damaged or scarred by this reflux. This is called reflux nephropathy

Reflux can occur in people whose ureters do not attach properly to the bladder or whose valves do not work well. Children may be born with this problem or may have other birth defects of the urinary system that cause reflux nephropathy.

Reflux nephropathy can occur with other conditions that lead to a blockage of urine flow, including:

• Bladder outlet obstruction, such as an enlarged prostate in men
• Bladder stones
• Neurogenic bladder, which can occur in people with multiple sclerosis, spinal cord injury, or other nervous system (neurological) conditions

Reflux nephropathy also can occur from swelling of the ureters after a kidney transplant or from injury to the ureter.

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