Metanephros: definitive kidney
The metanephros develops from three intermediate mesoderm structures of the sacral region:
- Ureter anlage (stage 14)
- Metanephric vesicle (stage 13)
- Glomerular capillary network (stage 13)
The ureter anlage is an epithelial diverticulum from the caudal part of the mesonephric duct (Wolffian duct) in the area of the first sacral vertebra (S1). The anlage intrudes into the metanephric vesicle and forms the extra- and intrarenal excretory passages.
The metanephric blastema corresponds to the sacral part of the nephrogenic cord below L3. It is mesenchymal tissue out of which the metanephric vesicles arise. From these originate the nephrons (= functional units of the kidneys).
At present it is still not clear whether the glomerular capillary network develops through vasculogenesis (direct development of vessels from the metanephric vesicles) or through angiogenesis (development from existing vessels of the metanephros).