At the fifth week of development, the ureteric bud arises as a diverticulum from the mesonephric (Wolfian) duct. The bud grows laterally and invades the center of the metanephrogenic blastema, the primordial renal tissue. The meeting of these two tissues causes changes in the bud and the metanephros. The metanephrogenic blastema forms glomeruli, proximal tubules and distal tubules. The ureteric bud divides and branches forming the renal pelvis, infundibulae, calyces, and collecting tubules which will provide a conduit for urine drainage in the mature kidney. This process is known as the induction of the kidney. See normal development of the ureter.
What happens if the ureteric bud fails to make contact with the metanephros? What happens if two ureteric buds arise from the mesonephric duct?
From 28 to 35 days of development, the ureter is patent, probably as a result of the mesonephros producing urine which fills the tube. From 37 to 40 days of development the ureter loses its lumen. At 40 days of development the ureter regains a lumen. Starting at the midpoint and progressing in both directions toward the developing kidney and the urogenital sinus, the lumen of the ureter reforms. The last segments of the ureter to gain a lumen are at either end (kidney or urogenital sinus). What happens if the ureter adjacent to the kidney never develops a lumen?
As development of the bladder progresses the mesonephric duct and the attached ureter are incorporated into the base of the bladder and the proximal urethra. In males, the mesonephric duct drains into the prostatic urethra as the ejaculatory duct. In females, the mesonephric duct regresses and the ureter alone remains. As the mesonephric duct and ureter are absorbed into the base of the bladder, they rotate so that the ureter meets the bladder cephalad to the point at which the mesonephric duct meets the urethra.
At the point where the ureter joins the urogenital sinus, a thin membrane (Chawalla's membrane) develops which separates the two lumens. This membrane then ruptures allowing passage of fetal urine into the urogenital sinus. What happens if this rupture is delayed?
At nine weeks of development the metanephros, which will become the mature kidney, starts to produce urine. As this fetal urine drains into the kidney, patency of the ureter is maintained. Smooth muscle develops in the ureteric wall. Later, this muscle will generate and propagate peristaltic contractions to conduct urine from the kidney to the bladder. What happens if the muscle fails to develop or if the muscle fails to conduct a peristaltic contraction?
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©David A. Hatch, M.D., 1996