Normal Development of the Kidney

David A. Hatch, M.D.

The pronephros arises as segmental collections of mesoderm in the cervical region at 3 weeks of development and then regresses at 4 weeks.

The mesonephros follows development of the pronephros and arises caudal to the pronephros at 4 weeks. The mesonephric vesicle, a collection of mesoderm, elongates to become a tubule. The medial end receives an invagination of capillaries, creating a Bowman's capsule while the lateral end of the tubule drains into the mesonephric duct. This maturation of mesonephric vesicals progresses in craino-caudad fashion. The caudal end of the mesonephric duct connects with the urogenital sinus. This junction will be important later in the developing male genital structures. The mesonephric duct is also known as the Wolfian duct.

The metanephros arises caudal to the mesonephros at 5 weeks of development. It derives from mesoderm, the metanephrogenic blastema, lateral to the developing urogenital sinus and lateral to the mesonephric duct.

The ureteric bud arises as a diverticulum from the mesonephric (Wolfian) duct and invades the center of the metanephros. This juxtaposition of the ureteric bud and the specialized mesoderm stimulates the metanephrogenic blastema to form glomeruli, proximal and distal tubules. When the ureteric bud touches the metanephros, progressive branching of the ureteric bud occurs creating the renal pelvis, infundibulae, calyces, and collecting tubules which will provide a conduit for urine drainage in the mature kidney. This process is known as the induction of the kidney. See pictures. What happens if the ureteric bud fails to make contact with the metanephros? What happens if two ureteric buds arise from the mesonephric duct?

As the kidney develops in the elongating fetus, it 'ascends' from its original location (adjacent to the developing bladder) to its mature location (in the retroperitoneum just caudal to the diaphragm). As the kidney moves cephalad relative to the bladder, it takes new arterial supply from the aorta and new venous drainage into the vena cava. This "ascent" is also accompanied by medial rotation. Early in development, the renal pelvis lies anterior to the renal parenchyma. As the kidney moves into the lumbar region, the renal pelvis rotates medially so that the renal parenchyma lies lateral to the pelvis. What happens if the kidney fails to ascend? What happens if the kidney develops more than one renal artery?

Look at abnormal renal development.

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©David A. Hatch, M.D., 1996