The normal ureter is a conduit to drain urine effectively at low pressures from the kidney to the bladder. At several points along its development abnormalities can occur which impair its function.
If the ureteric bud fails to arise from the mesonephric duct the metanephros will not be induced to form a kidney (renal agenesis). In some males, the mesonephric duct fails to form. In this case, neither a kidney nor a vas and epididymis will form although the testis may descend to its normal position in the scrotum.
In some females, neither the mesonephric (Wolfian) duct nor the paramesonephric (Müllerian) duct develop. In these girls, a kidney and oviduct are absent on the same side. This combination of renal, ureteric and genital abnormalities is known as the Meyer-Rokitansky Syndrome.
If the ureteric bud arises in an abnormal position on the mesonephric duct, it will not invade the center of the metanephrogenic blastema. Although contact with the periphery of the blastema may still result in the induction of a kidney, the induced renal tissue may be dysplastic. Although such a kidney will produce urine, it will not function normally.
The ureteric bud may arise from the mesonephric duct nearer to the urogential sinus (medial) than it should. This may result in renal dysplasia. In addition, as the rotational incorporation of the mesonephric duct and ureter into the developing bladder progresses, the ureteric orifice (where the ureter drains into the bladder) will finally lie lateral to and cephalad to the normal position in the developed bladder. In such cases, the tunnel through which the ureter travels into the bladder will be abnormally short. Vesicoureteric reflux ( abnormal flow of urine from the bladder up the ureter to the kidney) may result because the tunnel is too short to make a competent distal ureteric valve. This may explain why many kidneys with high grade reflux have abnormal function. The abnormal position of the ureteric bud results both in renal dysplasia (poor induction of the kidney) and also in reflux (abnormal position or ureteric orifice in the bladder). See more about reflux. See a case history of reflux.
If the musculature of the distal ureter is deficient or abnormal, that portion of the ureter will not conduct a peristaltic wave normally. Although the lumen of the ureter is of normal calibre, the lack of peristalsis through this portion effectively obstructs the flow of urine. The back-up of urine proximal to this aperistaltic segment causes dilation of the ureter and renal pelvis. This condition is referred to as megaureter for obvious reasons. See a case history of megaureter.
As the ureter develops, the distal end of the ureter (the point at which it meets the urogenital sinus) is covered with a thin layer of tissue (Chawalla's membrane). Normally the membrane ruptures allowing free passage of urine. If rupture of Chawalla's membrane is delayed, drainage of urine from the fetal kidney will be obstructed. Because Chawalla's membrane lies on the interior of the musculature of the developing bladder, the distal ureter (that portion inside the urogenital sinus) will be enlarged. This distal enlargement of the ureter within the bladder is called a ureterocele. See a case history of ureterocele.
The ureteric bud may arise farther from the urogenital sinus than it should. This may result in renal dysplasia as described above. In this case, however, the ureter will come to lie medial and distal to the normal position in the mature bladder. Should the ureteric bud arise still further lateral on the mesonephric duct, the mature ureter may open at the bladder neck, in the urethra, in the vagina (in females, of course) or on the vas deverens (in males). See a case history of ectopic ureter.
Return to G/U Development Home Page.
Questions or comments? Send e-mail to
David A. Hatch, M.D.
©David A. Hatch, M.D., 1996