During the third week of pregnancy, the process of gastrulation results in the formation of trilaminar embryo in humans. This is the beginning of morphogenesis (development of body form). Three germ layers, ectoderm, mesoderm, and endoderm, are present. A specific part of mesoderm, the intermediate mesoderm, gives rise to urogenital system gradually. It starts to develop from nephrogenic cord, which divides in nephrotomes. They give rise to pronephroi and subsequently mesonephroi, the transitory kidneys. Finally, metanephroi appear as the permanent organs, from two different structures: the metanephrogenic blastema (mesenchimal component) that leads to nephrons, and ureteric bud (epithelial component) that gives rise to collecting tubules, calices, renal pelvis, and ureter. Following developmental steps depend on inductive signaling between metanephrogenic blastema and ureteric bud.
Many genes, regulating proteins and pathways are involved in the physiological organogenesis. Cell proliferation and apoptosis keep the balance of the growth. Defects in these molecular and morphogenetic mechanisms may cause various congenital abnormalities of the kidney and urinary tract (CAKUT), which represent a family of diseases with a diverse anatomical spectrum.
