The kidney develops from the ureteric bud and the metanephric mesenchyme. The ureteric bud forms from an outgrowth of the mesonephric duct near the cloaca. The ureter, renal pelvis, major and minor calyces, collecting ducts and collecting tubules are all formed from the ureteric bud. The metanephric mesenchyme forms from the caudal portion of the intermediate mass, and it surrounds the end of the ureteric bud. Failure of the ureteric bud to contact the metanephric mesenchyme results in kidney agenesis. As the kidney grows the ureteric bud forms finger-like projections. The first 4 generations of the projections form the major calyx, the next 2 generations form the minor calyces, and the remaining projections form the straight and arched collecting tubules.
