Urinary Tract Embryology

The abdominal organs are derived primarily from endoderm, which forms the primitive gut tube. The gut tube is divided into 3 regions: foregut, midgut, and hindgut. The foregut gives rise to the lining of the GI tract from the esophagus to the upper duodenum, as well as the liver, gallbladder, and pancreas. The midgut gives rise to the GI tract lining between the midduodenum and midtransverse colon. The hindgut gives rise to the GI tract lining from the midtransverse colon through the upper anal canal. The mesoderm gives rise to the muscles of the GI tract wall, connective tissue (including the mesenteries and omenta), and the vasculature. The ectoderm gives rise to the nerve tissue and the lining of the lower anal canal.

The urogenital system is derived from intermediate mesoderm. The intermediate mesoderm differentiates into nephrogenic cords (which will go on to form the urinary system) and an adjacent area known as the gonadal ridge (which will go on to form the gonads). The nephrogenic cords elongate in a caudal direction and sequentially develop 3 different structures: the pronephros (rudimentary and nonfunctional), the mesonephros (forms the primitive urinary system), and the metanephros (forms the permanent kidney). Concurrently, the genital system develops in close association with the urinary system. Genital development depends on chromosomal sex, which determines whether the primitive gonads differentiate into testes or ovaries. The gonads then secrete certain hormones, which direct further development of both the internal and external genital structures.