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The intermediate mesoderm gives rise to the kidney. Three pairs of kidney make an appear­ance in succession during development: pronephros, mesonephros and metanephros or permanent kidneys. Permanent kidneys develop from metanephric diverticulum (ureteric bud) and metanephric blastema. The ureteric bud gives rise to the ureter, renal pelvis, major and minor calyces, and approximately one to three million collecting tubules, whereas the metanephric blastema gives rise to nephrons. The collecting tubules penetrate the metanephric blastema, and they induce the formation of renal vesicles. Renal vesicles give rise to small tubules, which form nephrons or excretory unit (Bowman’s capsule, proximal convoluted tubule, loop of Henle, and distal convoluted tubule). Urogenital sinus gives rise to urinary bladder and the uretra. Ureters are of mesodermal origin, whereas the epithelium of urinary bladder is of endodermal origin.