Ureterbud

Ureterbud, or ureteric bud, is an embryonic outgrowth of the distal Wolffian (mesonephric) duct that initiates the development of the kidney's collecting system. It emerges during early gestation and guides the formation of the ureter and the collecting ducts.

In human development, the ureteric bud grows toward the surrounding metanephric mesenchyme. Through reciprocal induction with this mesenchyme, the bud undergoes branching morphogenesis to form the renal pelvis, calyces, and collecting ducts. Signaling pathways driving this process include GDNF secreted by the metanephric mesenchyme acting through the RET receptor on the bud, as well as WNT11 and various fibroblast growth factors that coordinate branching and differentiation.

The ureteric bud's primary function is to establish the kidney’s collecting system, but it also induces nephron formation in the metanephric mesenchyme, contributing to overall nephron development and kidney organogenesis.

Clinical significance: Abnormal ureteric bud development or signaling can lead to congenital anomalies of the kidney and urinary tract (CAKUT). Examples include renal agenesis or hypoplasia from failed bud formation, duplex or duplicated collecting systems from abnormal budding, ureteropelvic junction obstruction, and improper insertion of the ureter into the bladder, which can contribute to reflux or obstruction.

Etymology and terminology: The term ureterbud is used in German; in English the preferred term is ureteric bud or ureter bud.