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Illustration of renal development. A. Transverse view of early embryo, illustrating the formation of the urogenital ridge and nephrogenic cord from  the intermediate mesoderm. B. Lateral view of early embryo summarizng relative cranial to caudal progression of renal development;  not specific for any particular period during embryonic development.  
 
Overview
  • Kidney development
    • progresses in a cranial to caudal direction
    • intermediate mesoderm → urogenital ridge → nephrogenic cord → urinary system
  • Pronephros
    • non-functional
    • appears by week 4
    • degenerates by week 5
  • Mesonephros
    • development induced by pronephric duct
    • forms mesonephric duct (Wolffian duct)
    • interim kidney for 1st trimester
    • opens into urogenital system and gives rise to male genital system
  • Metanephros
    • develops from mesonephric outgrowth called ureteric bud during week 5
    • fully canalized and functioning at week 10
    • nephrogenesis continues through 32 - 36 weeks of gestation
    • derivatives include
      • ureteric bud develops into
        • ureter
        • pelvises
        • calyces and collecting ducts 
        • aberrant development may result in congenital malformations of the lower urinary tract
      • metanephric mesenchyme
        • interaction with ureteric bud causes metranephric mesenchyme to differentiate the renal structures from collecting tubules to glomerulus
        • abnormal interaction with ureteric bud may cause malformations
  • Ureteropelvic junction with kidney
    • canalizes last
    • most common site of obstruction in fetus which results in hydronephrosis 
  • Adult kidney
    • embryo grows faster caudally causing a change in location of the kidney from S1 - S2 to a final position of T12 - L3
Developmental Abnormalities
  • Renal agenesis
    • failure of ureteric buds to form → no kidney formation
  • Potter's Syndrome 
    • bilateral renal agensis oligohydramnios → fetal compression resulting in
      • limb deformities
        • clubbed feet 
      • facial deformities
      • pulmonary hypoplasia  
  • Horseshoe kidney
    • fusion of inferior poles of kidneys 
      • ascension of kidney is prevented by the inferior mesenteric artery and remain low in abdomen - may cause other renal vascular anomalies.
      • normal kidney function
This is an illustration comparing normal kidney ascent with a horseshoe kidney, where the ascent gets arrested by the IMA. 
 

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