20.2 Development of the renal anlage



Metanephros: definitive kidney


The metanephros develops from three intermediate mesoderm structures of the sacral region:

  • Ureter anlage 14
  • Metanephric vesicle 13
  • Glomerular capillary network 13


The ureter anlage 14 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 13 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) (5). 		Fig. 9 - Development of the metanephros: 5th week  Legend

1a
1b
2

3
4
5
6
7		 Pronephros (atrophying)
Mesonephros (atrophying)
Mesonephric duct
(Wolffian duct)
Nephrogenic cord
Ureter anlage
Metanephric blastema
Liver anlage
Cloaca

Fig. 9
Sagittal section of a 5-week-old embryo - development of the metanephros.
In the caudal region of the nephrogenic cord one observes the development of the metanephro-
genic blastema that is in contact with the ureter anlage. In this stage the pronephros has disappeared almost completely. The mesonephros is also in the process of atrophying.


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