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Common Urological Problems

Upper urinary tract

  • - Paediatric Urology - Embryology
  • Jun 17, 2010
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Tags: | cystic anomalies | genitourinary tract | metanephric blastema | metanephros |

In the cervical portions of the paired blocks of intermediate mesoderm the primitive precursor of the kidney,  the pronephros,  first appears in the fourth week of gestation. 

This structure rapidly regresses in the human embryo.  The midzone mesonephros, however, continues to differentiate, giving rise to tubular structures which,  although ultimately destined to contribute to the definitive gonad,  function briefly in an excretory role.  In the mesenchyme lying lateral to the developing mesonephros, the mesonephric ducts appear, advancing caudally to fuse with the terminal portion of the hindgut (the primitive cloaca).

Canalisation of the mesonephric ducts creates a patent excretory unit which is believed to function transiently.

At the beginning of the fifth week, the ureteric buds arise from the distal portion of the paired mesonephric ducts and advance towards the most caudal portion of the blocks of intraembryonic mesoderm -  the metanephros.  Fusion of the ureteric bud and metanephric blastema at around 32 days initiates the process of nephrogenesis.

Embryonic   precursors   of   the   upper urinary tract, metanephros, ureteric budFigure   1.3   Embryonic   precursors   of   the   upper urinary tract, metanephros (kidney), ureteric bud.

Embryonic  genitourinary  tract  at  6-8 weeksFigure 1.4   Embryonic genitourinary tract at 6-8 weeks.

At the beginning of the fifth week, the ureteric buds arise from the distal portion of the paired mesonephric ducts and advance towards the most caudal portion of the blocks of intraembryonic mesoderm -  the metanephros.  Fusion of the ureteric bud and metanephric blastema at around 32 days initiates the process of nephrogenesis.

Between the sixth and 10th weeks the lobulated embryonic   kidneys   ascend   up   the   posterior abdominal   wall,  deriving   their   blood   supply sequentially at different levels until the definitive lumbar position is achieved (Figure 1.4).

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