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- What are the types of defects in the urinary tract?
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The urinary tract consists of
- two kidneys, which filter waste materials and excess water from the blood
- two ureters, which carry urine from the kidneys to the bladder
- the bladder, where urine is stored until it is released
- the urethra, where urine flows out of the body
We rely on our kidneys and urinary system to keep fluids and natural chemicals in our bodies balanced. While a baby is developing in the mother's womb, much of that balancing is handled by the mother's placenta. The baby's kidneys begin to produce urine at about 10 to 12 weeks after conception, but the mother's placenta continues to do most of the work until the last few weeks of the pregnancy. Wastes and excess fluid are removed from the baby's body through the umbilical cord. The baby's urine is released into the amniotic sac and becomes part of the amniotic fluid. This fluid plays a role in the baby's lung development.
Sometimes, a birth defect in the urinary tract will block the flow of urine in an unborn baby. As a result, urine backs up and causes the ureters and kidneys to swell. Swelling in the kidneys is called hydronephrosis. Swelling in the ureters is called hydroureter.
Hydronephrosis is the most common problem found during ultrasound examination of babies in the womb. The swelling may be barely detectable or very noticeable. The results of hydronephrosis may be mild or severe, but the long-term outcome for the child's health cannot always be judged by the severity of swelling. Urine blockage may damage the developing kidneys and reduce their ability to filter. The blockage may also raise the risk that the child will develop a urinary tract infection (UTI). Recurring UTIs can lead to more permanent kidney damage. In the most severe cases of urine blockage, the amniotic sac is so reduced that the lack of fluid threatens the baby's lung development.
Types of Defects in the Urinary Tract
Hydronephrosis can result from many types of defects in the urinary tract. Doctors use specific terms to describe the type and location of the blockage.
- Vesicoureteral reflux (VUR). The openings where the ureters empty urine into the bladder should work like valves to keep urine from backing up into the ureters. Sometimes the valve doesn't work properly and urine flows back into the kidneys. The urine may flow only a short way back into the ureters, or it may go all the way back to the kidneys, causing the ureters and kidneys to swell. VUR may occur in only one ureter or in both. Kidneys with severe reflux may not develop normally, and after birth kidneys with reflux may be at risk for damage from infections.
- Ureteropelvic junction (UPJ) obstruction. The point where the ureter joins the kidney is called the ureteropelvic junction. If urine is blocked here, only the kidney swells. The ureter remains at a normal size. UPJ obstruction usually only occurs in one kidney.
- Bladder outlet obstruction (BOO). BOO describes any blockage in the urethra or at the opening of the bladder. The obstruction may occur in boys or girls. The most common form of BOO seen in newborns and during prenatal ultrasound examinations is posterior urethral valves (PUV). BOO caused by PUV occurs only in boys.
- Posterior urethral valves (PUV). In boys, sometimes an abnormal fold of tissue in the urethra keeps urine from flowing freely out of the bladder. This defect may cause swelling in the entire urinary tract, including the urethra, bladder, ureters, and kidneys.
- Ureterocele. If the end of the ureter does not develop normally, it can bulge, creating what is called a ureterocele. The ureterocele may obstruct part of the kidney or the bladder.