Summery
In a cranial to caudal sequence, three sets of excretory organs develop in human embryos: pronephros, mesonephros and metanephros.
Pronephros form in the cervical region and degenerate by the end of the fourth week.
Metanephros is large and characterized by its own collecting duct or walffian duct.
Metanephrons develop from two different sources: the metanephric diverticulum (ureteric bud), which is the primordium of the ureter, the renal pelvic, the calices and the collecting tubules. The second is the metanephric mass of the intermediate mesoderm (metanephric blastema), which would form the nephrons.
The mesenchyme expresses WT1 which enables the tissue to respond to induction by the ureteric bud. GDNF and HGF are regulated by WT1 and stimulate the branching and growth of the ureteric bud. FGF2and BMP7secreted by the bud and stimulate proliferation in the metanephric mesenchyme and maintain expression of WT1. PAX2 and WNT4 regulated by WNT9B and WNT6, promote condensation and epithelisation of the mesenchyme to form tubules.
While medially rotating by 90 degrees, the kidneys leave their original pelvic position and gradually ascend to the abdomen. The blood supply of the kidney changes during the ascend.
Many congenital abnormalities could occur during the developmental process of the urinary system.
Pronephros form in the cervical region and degenerate by the end of the fourth week.
Metanephros is large and characterized by its own collecting duct or walffian duct.
Metanephrons develop from two different sources: the metanephric diverticulum (ureteric bud), which is the primordium of the ureter, the renal pelvic, the calices and the collecting tubules. The second is the metanephric mass of the intermediate mesoderm (metanephric blastema), which would form the nephrons.
The mesenchyme expresses WT1 which enables the tissue to respond to induction by the ureteric bud. GDNF and HGF are regulated by WT1 and stimulate the branching and growth of the ureteric bud. FGF2and BMP7secreted by the bud and stimulate proliferation in the metanephric mesenchyme and maintain expression of WT1. PAX2 and WNT4 regulated by WNT9B and WNT6, promote condensation and epithelisation of the mesenchyme to form tubules.
While medially rotating by 90 degrees, the kidneys leave their original pelvic position and gradually ascend to the abdomen. The blood supply of the kidney changes during the ascend.
Many congenital abnormalities could occur during the developmental process of the urinary system.