ABSTRACT
During the 4th week of gestation, the development of the ureter begins as an outpouching of the
mesonephric duct, termed the ureteric bud (Figure 35.1). The development of this structure is heavily influenced by molecular factors released from the mesodermal tissue mass, which is destined to become the renal parenchyma (i.e. the metanephric blastema). At 28 days, the ureter consists of an epithelial tube surrounded by loose mesenchymal cells. Transient luminal obstruction ensues, with subsequent recanalization during the 7th week of gestation.1,2 It appears that this recanalization process begins in the midureter and extends in a bidirectional manner both cranially and caudally. It has been suggested that angiotensin exerts its affect through the angiotensin 2 receptor (AT2) and may play a role in this recanalization process.3 Chwalle’s membrane, a two-layered cell structure, transiently divides the early ureteric bud from the urogenital sinus.4 Subsequent dissolution of this membrane results in unimpeded flow of urine from the kidney into the bladder.
