Renal development begins in-utero and continues throughout childhood. Almost one-third of all developmental
anomalies include structural or functional abnormalities of the urinary tract. There are three main phases of in-utero renal
development: Pronephros, Mesonephros and Metanephros. Within three weeks of gestation, paired pronephri appear. A
series of tubules called nephrotomes fuse with the pronephric duct. The pronephros elongates and induces the nearby
mesoderm, forming the mesonephric (Woffian) duct. The metanephros is the precursor of the mature kidney that originates
from the ureteric bud and the metanephric mesoderm (blastema) by 5 weeks of gestation. The interaction between
these two components is a reciprocal process, resulting in the formation of a mature kidney. The ureteric bud forms the
major and minor calyces, and the collecting tubules while the metanephrogenic blastema develops into the renal tubules
and glomeruli. In humans, all of the nephrons are formed by 32 to 36 weeks of gestation. Simultaneously, the lower urinary
tract develops from the vesico urethral canal, ureteric bud and mesonephric duct. In utero, ureters deliver urine from
the kidney to the bladder, thereby creating amniotic fluid. Transcription factors, extracellular matrix glycoproteins, signaling
molecules and receptors are the key players in normal renal development. Many medications (e.g., aminoglycosides,
cyclooxygenase inhibitors, substances that affect the renin-angiotensin aldosterone system) also impact renal development
by altering the expression of growth factors, matrix regulators or receptors. Thus, tight regulation and coordinated
processes are crucial for normal renal development.
The United States Food and Drug Administration, Office of Device Evaluation, Center for Devices and Radiological Health, Renal Devices Branch, Silver Spring, Maryland, USA.